Abstract
BACKGROUND
There are known differences in the risk of perinatal and maternal birth outcomes because of maternal factors, such as body mass index and maternal race. However, the association of maternal height with adverse birth outcomes and the potential differences in this relationship by race and ethnicity have been understudied.
OBJECTIVE
This study aimed to examine the association between maternal stature and adverse perinatal outcomes and the potential modification of the association by race and ethnicity.
STUDY DESIGN
This retrospective cohort study was conducted using data on all singleton births in the United States in 2016 and 2017 (N=7,361,713) obtained from the National Center for Health Statistics. Short and tall stature were defined as <10th and >90th percentiles of the maternal height distribution (<154.9 and >172.7 cm, respectively). Race and ethnicity categories included non-Hispanic White, non-Hispanic Black, American Indian or Alaskan Native Asian or Pacific Islander, and Hispanic. The primary outcomes were preterm birth (<37 weeks of gestation), perinatal death, and composite perinatal death or severe neonatal morbidity. Logistic regression was used to obtain adjusted odds ratios and 95% confidence intervals with adjustment for confounding by maternal age, body mass index, and other factors. Multiplicative and additive effect modifications by race and ethnicity were assessed.
RESULTS
The study population included 7,361,713 women with a singleton stillbirth or live birth. Short women had an increased risk of adverse outcomes, whereas tall women had a decreased risk relative to average-stature women. Short women had an increased risk of perinatal death and composite perinatal death or severe neonatal morbidity (adjusted odds ratios, 1.14 [95% confidence interval, 1.10–1.17] and 1.21 [95% confidence interval, 1.19–1.23], respectively). The association between short stature and perinatal death was attenuated in non-Hispanic Black women compared with non-Hispanic White women (adjusted odds ratio, 1.10 [95% confidence interval, 1.03–1.17] vs 1.26 [95% confidence interval, 1.19–1.33]). Compared with average-stature women, tall non-Hispanic White women had lower rates of preterm birth, perinatal death, and composite perinatal death or severe neonatal morbidity (adjusted odds ratios, 0.82 [95% confidence interval, 0.81–0.83], 0.95 [95% confidence interval, 0.91–1.00], and 0.90 [95% confidence interval, 0.88–0.93], respectively). The association between tall and average stature with perinatal death was reversed in Hispanic women (adjusted odds ratio, 1.27; 95% confidence interval, 1.12–1.44). Compared with average-stature women, all tall women had lower rates of preterm birth, particularly among non-Hispanic Black and Hispanic women.
CONCLUSION
Relative to average-stature women, short women have an increased risk of adverse perinatal outcomes across all race and ethnicity groups; these associations were attenuated in Hispanic women and for some adverse outcomes in non-Hispanic Black and Asian women. Tall mothers have a lower risk of preterm birth in all racial and ethnic groups, whereas tall non-Hispanic White mothers have a lower risk of perinatal death or severe neonatal morbidity compared with average-stature women.
Key words: large for gestational age, maternal height, perinatal death, preterm birth, race and ethnicity, severe neonatal morbidity, small for gestational age
AJOG Global Reports at a Glance.
Why was this study conducted?
The association between maternal height and adverse birth outcomes is understudied, including possible effect modifications by race and ethnicity. Maternity care providers need to recognize perinatal risks associated with maternal stature and how these risks vary by maternal race and ethnicity.
Key findings
Short women had an increased risk of preterm birth (PTB; <37 weeks of gestation), perinatal death, and composite perinatal death or severe neonatal morbidity, whereas tall women had a decreased risk of PTB and composite perinatal death or severe neonatal morbidity. These associations were weaker in Hispanic women of short stature compared with non-Hispanic White women.
What does this add to what is known?
Maternal height was associated with serious adverse perinatal outcomes, independent of prepregnancy body mass index and other maternal characteristics, and these associations were modified by race and ethnicity.
Introduction
Although prepregnancy body mass index (BMI), derived from an individual's weight and height, is well known for its association with adverse perinatal outcomes,1, 2, 3, 4 few studies have investigated the association between maternal height and adverse perinatal events. Nevertheless, there is reason to believe that maternal height has a bearing on perinatal outcomes that is independent of BMI because height reflects the aspects of health related to genetic potential, nutrition during childhood and adolescence, and socioeconomic and cultural factors. The few studies that have studied the association between maternal height and perinatal outcomes show that height is an independent predictor of adverse pregnancy outcomes, including gestational diabetes mellitus, fetal growth restriction (FGR), cesarean delivery, cephalopelvic disproportion, and preterm birth (PTB).5, 6, 7, 8, 9, 10, 11
Associations between maternal height and adverse perinatal outcomes are likely to be modified by race and ethnicity. Large differences exist in mean maternal height and other factors between women of various races and ethnicities, and substantial differences are also observed concerning adverse perinatal outcomes.12, 13, 14 Many studies have highlighted increased rates of adverse outcomes, such as PTB, FGR, stillbirth, and infant mortality and morbidity, in non-Hispanic Black mothers compared with non-Hispanic White women.12,15, 16, 17, 18 Similarly, American Indian and Alaskan Native (AIAN) women are at increased risk of gestational diabetes mellitus and hypertension, eclampsia, blood transfusion, admission to the intensive care unit (ICU), and large-for-gestational-age (LGA) infants, PTB, and infant morbidity and mortality.14,16,17 Asian mothers are more likely to have severe perineal lacerations,12,15,16 and Hispanic mothers are reported to have an increased risk of gestational diabetes mellitus and congenital anomalies.12,15,19 In contrast, Hispanic mothers have a lower risk of some adverse pregnancy outcomes, such as PTB and infant mortality, than non-Hispanic White women.12,14,17,19 There are reasonable grounds for expecting the associations between maternal height and adverse perinatal outcomes to be modified by race and ethnicity as the mechanisms underlying height differences (eg, nutrition during childhood and adolescence and socioeconomic and cultural factors) likely vary by race and ethnicity.20
Therefore, we conducted a study to quantify the associations between maternal stature and adverse maternal and perinatal outcomes and to examine whether these associations are modified by maternal race and ethnicity.
Material and Methods
We conducted a retrospective cohort study that included all singletons born in the United States in 2016 and 2017. Data were obtained from the publicly available US cohort-linked birth-infant death files and fetal death files maintained by the National Center for Health Statistics (NCHS).21 The NCHS uses a variety of data collection mechanisms, including standardized forms and training, to maintain high data accuracy and completeness.22 The linked birth-infant death files included information about maternal demographic and clinical characteristics, pregnancy complications, and neonatal outcomes for approximately 99.0% of births in the United States. This information was abstracted from live birth and fetal death certificates by trained personnel and included maternal age, self-reported height and prepregnancy weight, obstetrical history (previous adverse outcomes), maternal comorbidity (eg, prepregnancy diabetes mellitus and hypertension), pregnancy complications (eg, gestational hypertension), and other clinical data related to childbirth (eg, gestational age at delivery and mode of delivery), stillbirth or live birth, 5-minute Apgar score, birthweight, congenital anomalies, and neonatal resuscitation. All singleton live births and fetal deaths between 20 and 43 weeks of gestation, based on the clinical estimate of gestation, were included, whereas births with missing prepregnancy BMI, and those with implausible or highly unlikely values for maternal height (<130 or >230 cm) were excluded.
Maternal height, race and ethnicity
Maternal height was categorized using percentiles of the study population's height distribution. Short stature was defined as height in the lowest decile (<10% of the height distribution: <154.9 cm), whereas tall stature was defined as height within the highest decile (>90% of the height distribution: >172.7 cm). Average-stature women included those with heights between the 10th and 90th percentiles of the overall height distribution. Self-reported race categories included White, Black or African American, AIAN, Asian Indian, Chinese, Filipino, Japanese, Korean, Vietnamese, other Asian, Native Hawaiian, Guamanian, Samoan, other Pacific Islander, and more than one race. Ethnicity was self-reported as being Hispanic, including Mexican, Mexican American, Chicana, Puerto Rican, Cuban, and other Spanish, Hispanic, or Latina origin. From this information, we categorized race and ethnicity as non-Hispanic White, non-Hispanic Black, AIAN, Asian or Pacific Islander (Asian Indian, Chinese, Filipino, Japanese, Korean, Vietnamese, other Asian, Native Hawaiian, Guamanian or Chamorro, Samoan, and other Pacific Islander), and Hispanic (all women of Hispanic origin, regardless of race). The categories of maternal race and ethnicity were based on previous literature15,16,18 and the terminology used in the US National Vital Statistics Reports (Appendix 1).23
Adverse birth outcomes
The primary outcomes were PTB at <37 weeks of gestation, perinatal mortality (fetal death or neonatal death <28 days after birth), and composite perinatal mortality or severe neonatal morbidity. Composite perinatal mortality or severe neonatal morbidity included any of the following: perinatal death, 5-minute Apgar score of <4, neonatal seizures, and ventilation for >6 hours. The secondary outcomes included PTB at <34 weeks of gestation, small-for-gestational-age (SGA) infant (birthweight for gestational age of <10th percentile),24 LGA infant (birthweight for gestational age of >90th percentile),24 macrosomia (birthweight of ≥4500 g), neonatal ICU (NICU) admission, and composite maternal morbidity. Composite maternal morbidity was defined as any of the following: ICU admission, blood transfusion, uterine rupture, unplanned hysterectomy, and eclampsia.
Statistical analyses
Demographic and clinical characteristics were compared by stature; moreover, we compared distributions of maternal stature among women with various characteristics. The rates of PTB and neonatal mortality and morbidity were expressed per 100 live births, whereas other outcomes, which included fetal death, were expressed per 100 total births. Logistic regression models were used to examine the independent association between maternal stature and the primary outcomes: PTB (<37 weeks of gestation), perinatal mortality, and composite perinatal mortality or severe neonatal morbidity. Logistic regression models included interaction terms between stature and race and ethnicity to assess whether these associations between maternal height and the adverse perinatal outcomes were significantly modified by race and ethnicity (multiplicative interaction). Short and tall women were compared with average-height women (reference group) within each race and ethnicity category. Linear binomial regression models were used to assess adjusted risk differences (ARDs) between short and tall- vs average-stature women and effect modification by race and ethnicity (additive interaction). ARDs were obtained for women with no additional risk factor (ie, covariates set to reference values). The likelihood ratio test was used to assess the significance of the additive interaction terms. The models adjusted for nulliparity (defined as no previous live births or stillbirths), prepregnancy BMI (categorized as underweight [<18.5 kg/m2], normal [18.5–24.9 kg/m2], overweight [25.0–29.9 kg/m2], obese class I [30.0–34.9 kg/m2], obese class II [35.0–39.9 kg/m2], and obese class III [≥40 kg/m2]), education (less than high school vs high school or higher education), maternal age (<25, 25–34, and ≥35 years), type of healthcare insurance (private insurance, Medicaid, self-pay, or other), congenital anomalies, chronic hypertension, chronic diabetes mellitus, prenatal care (no reported prenatal care and any), and fetal sex (male and female). The multivariable analyses of perinatal death and composite death or severe neonatal morbidity did not include the type of healthcare insurance because this information was not available on fetal death certificates. Information about congenital anomalies was available from live birth certificates and included anencephaly, meningomyelocele or spina bifida, omphalocele, gastroschisis, limb reduction defects, cleft lip, cleft palate, cyanotic congenital heart disease, congenital diaphragmatic hernia, Down syndrome, chromosomal disorders (suspected or confirmed), and hypospadias.
To investigate the effect of maternal height, as a continuous variable, on perinatal mortality, composite perinatal mortality or severe neonatal morbidity, and PTB (<37 weeks of gestation), we used logistic regression with restricted cubic splines to model maternal height, adjusted for the covariates as described above. We graphed the predicted probability of the primary outcomes associated with maternal height (continuous) from these models with 5 knots equally spaced along the x-axis for each race and ethnicity group while holding the values of other covariates constant (set to the mean or the most frequent values in the study population). All analyses were performed using SAS (version 9.4; SAS Institute, Inc, Cary, NC) and R (version 4.0.3).
The study was based on publicly accessible deidentified data and did not require ethics approval. No patient was involved. Patients or the public were not involved in the design, conduct, reporting, or dissemination plans of our research.
Results
There were 7,576,417 singleton live births and stillbirths in the United States in 2016 and 2017. Data excluded were 9101 births before 20 weeks of gestation and after 43 weeks of gestation (0.1%). In addition, 205,603 women (2.7%) who had implausible or missing values for height and BMI were excluded. The study population included 7,361,713 women (97.2%) with singleton births (Appendix Figure 1).
Overall, 9.3% of women had short stature (<154.9 cm), 84.3% of women had an average height (154.9–172.7 cm), and 6.3% of women were classified as tall (>172.7 cm) (Table 1). Tall women were more likely to be educated (93.8% of women had an education above high school), be married (63.1%), smoke during pregnancy (7.9%), and use private healthcare insurance (60.1%) (Table 1). In contrast, short women were more likely to be less educated (27.1% of women had less than high school education), be younger than 25 years of age (31.9%), and use Medicaid (56.0%) (Table 1).
Table 1.
Maternal height categories and maternal characteristics in women with singleton births in the United States, 2016–2017
| Maternal stature |
||||
|---|---|---|---|---|
| Maternal characteristics | Short (n=687,427) | Average (n=6,207,630) | Tall (n=466,656) | |
| Race and ethnicity | Non-Hispanic White | 199,867 (29.1) | 3,407,497 (54.9) | 339,059 (72.7) |
| Non-Hispanic Black | 78,630 (11.4) | 936,293 (15.1) | 82,248 (17.6) | |
| American Indian or Alaska Native | 4433 (0.6) | 59,318 (1.0) | 4225 (0.9) | |
| Asian or Pacific Islander | 85,535 (12.4) | 433,663 (7.0) | 7554 (1.6) | |
| Hispanic | 318,962 (46.4) | 1,370,859 (22.1) | 33,570 (7.2) | |
| Body mass index (kg/m2) | Underweight (<18.5) | 17,185 (2.5) | 215,197 (3.5) | 23,063 (4.9) |
| Normal (18.5–24.9) | 266,291 (38.7) | 2,759,328 (44.5) | 208,064 (44.6) | |
| Overweight (25.0–29.9) | 214,766 (31.2) | 1,596,840 (25.7) | 113,366 (24.3) | |
| Obese I (30.0–34.9) | 108,106 (15.7) | 894,569 (14.4) | 62,334 (13.4) | |
| Obese II (35.0–39.9) | 50,172 (7.3) | 432,318 (7.0) | 35,009 (7.5) | |
| Obese III (≥40.0) | 30,907 (4.5) | 309,378 (5.0) | 24,820 (5.3) | |
| Maternal age (y) | <25 | 219,259 (31.9) | 1,582,638 (25.5) | 86,611 (18.6) |
| 25–34 | 360,725 (52.5) | 3,574,352 (57.6) | 287,354 (61.6) | |
| ≥35 | 107,443 (15.6) | 1,050,640 (16.9) | 92,691 (19.9) | |
| Parity | 0 birth | 242,529 (35.3) | 2,406,019 (38.8) | 186,379 (39.9) |
| 1–3 births | 399,281 (58.1) | 3,475,619 (56.0) | 257,996 (55.3) | |
| ≥4 births | 43,810 (6.4) | 309,137 (5.0) | 20,975 (4.5) | |
| Married or common law | Yes | 317,524 (46.2) | 3,520,440 (56.7) | 294,569 (63.1) |
| No | 311,969 (45.4) | 2,287,855 (36.9) | 148,663 (31.9) | |
| Missing | 57,934 (8.4) | 399,335 (6.4) | 23,424 (5.0) | |
| Education | Less than high school | 183,474 (26.7) | 771,155 (12.4) | 29,142 (6.2) |
| Cigarette smoking during pregnancy | 37,663 (5.5) | 445,520 (7.2) | 36,991 (7.9) | |
| Healthcare insurance | Medicaid | 381,173 (55.4) | 2,589,366 (41.7) | 150,889 (32.3) |
| Private insurance | 230,062 (33.5) | 3,076,974 (49.6) | 280,543 (60.1) | |
| Self-pay | 39,841 (5.8) | 241,752 (3.9) | 13,714 (2.9) | |
| Other payment | 29,075 (4.2) | 235,418 (3.8) | 16,558 (3.5) | |
Missing values of <3% are not shown.
Yearwood. Maternal height and adverse birth outcomes. Am J Obstet Gynecol Glob Rep 2023.
Approximately 54% of women were non-Hispanic White, 23% were Hispanic, 15% were non-Hispanic Black, 7% were Asian or Pacific Islander, and 1% were AIAN. Tall women were more likely to be non-Hispanic White (72.7%), whereas short women were more likely to be Hispanic (46.4%) (Table 1). Within the racial and ethnic categories, non-Hispanic Whites and non-Hispanic Blacks had the largest proportions of tall women, and Asian and Hispanic women had the largest proportions of short women (Table S1).
Short women had the lowest frequency of hypertension in pregnancy (5.3%), previous fetal death or pregnancy termination (24.7%), and labor induction (21.5%), whereas tall women had the highest frequency of hypertension in pregnancy (7.0%), previous fetal death or pregnancy termination (27.7%), and labor induction (29.4%) (Table 2).
Table 2.
Obstetrical history and related characteristics by maternal height in women with singleton births in the United States, 2016–2017
| Maternal stature |
|||
|---|---|---|---|
| Obstetrical history and characteristics | Short (n=687,427) | Average (n=6,207,630) | Tall (n=466,656) |
| Previous cesarean delivery | 136,676 (19.9) | 934,285 (15.1) | 58,456 (12.5) |
| Previous fetal death or termination | 169,948 (24.7) | 1,646,387 (26.5) | 129,212 (27.7) |
| Previous infant death | 9810 (1.4) | 75,478 (1.2) | 5560 (1.2) |
| Prepregnancy diabetes mellitus | 6620 (1.0) | 54,524 (0.9) | 4691 (1.0) |
| Prepregnancy hypertension | 9349 (1.4) | 110,201 (1.8) | 11,824 (2.5) |
| Hepatitis (B or C) | 4434 (0.6) | 40,733 (0.7) | 2874 (0.6) |
| No prenatal care | 13,463 (2.0) | 88,786 (1.4) | 5876 (1.3) |
| Prenatal care initiation in the first trimester of pregnancy | 482,846 (70.2) | 4,722,422 (76.1) | 367,125 (78.7) |
| Infertility treatment | 5311 (0.8) | 85,211 (1.4) | 8896 (1.9) |
| Assisted reproductive technology | 2954 (0.4) | 47,425 (0.8) | 4950 (1.1) |
| Hypertension in pregnancy | 36,716 (5.3) | 371,553 (6.0) | 32,744 (7.0) |
| Gestational diabetes mellitus | 55,362 (8.1) | 371,192 (6.0) | 21,644 (4.6) |
| Labor induction | 147,673 (21.5) | 1,602,465 (25.8) | 137,253 (29.4) |
| Forceps | 3357 (0.8)a | 34,259 (0.8)a | 2528 (0.7)a |
| Vacuum | 18,098 (4.2)a | 163,367 (3.8)a | 10,930 (3.2)a |
| Cesarean delivery | 258,829 (37.7) | 1,856,200 (29.9) | 120,239 (25.8) |
| Chorioamnionitis | 15,239 (2.2) | 95,872 (1.5) | 4551 (1.0) |
| Male | 350,694 (51.0) | 3,178,177 (51.2) | 239,095 (51.2) |
| Gestational age at delivery (wk) | |||
| 20–23 | 2269 (0.3) | 19,075 (0.3) | 1429 (0.3) |
| 24–27 | 3532 (0.5) | 25,663 (0.4) | 1783 (0.4) |
| 28–33 | 14,146 (2.1) | 98,190 (1.6) | 6299 (1.4) |
| 34–36 | 49,894 (7.3) | 364,367 (5.9) | 23,642 (5.1) |
| 37–38 | 195,736 (28.5) | 1,554,665 (25.0) | 107,595 (23.1) |
| 39–43 | 421,850 (61.4) | 4,145,670 (66.8) | 325,908 (69.8) |
| Birth weight (g) | |||
| <1500 | 11,265 (1.6) | 80,449 (1.3) | 5323 (1.1) |
| 1500–2499 | 56,696 (8.3) | 324,949 (5.2) | 16,231 (3.5) |
| 2500–4499 | 616,114 (89.6) | 5,732,958 (92.4) | 432,266 (92.6) |
| ≥4500 | 3352 (0.5) | 69,274 (1.1) | 12,836 (2.8) |
Hypertension in pregnancy includes gestational hypertension and preeclampsia.
Per 100 vaginal deliveries; P values for differences between categories were P=.020 for male sex, P=.030 for hepatitis, and P<.0001 for all other characteristics.
Yearwood. Maternal height and adverse birth outcomes. Am J Obstet Gynecol Glob Rep 2023.
Outcome rates
Short women had the highest rates of all adverse fetal and infant outcomes, except for LGA and macrosomia (Figure 1, A, and Table S2); moreover, they had slightly higher rates of composite maternal morbidity (Figure 1, B, and Table S3). For instance, PTB (<37 weeks of gestation) occurred in 10.2% of short women compared with 8.2% of average-height women and 7.1% of tall women (Figure 1, A, and Table S2). The rates of adverse outcomes differed by race and ethnicity (Table S4). In general, higher rates of adverse fetal and infant outcomes were observed in non-Hispanic Black and AIAN women. For example, the rates of perinatal death and neonatal morbidity in non-Hispanic White women of short, average, and tall stature were 2.8%, 2.1%, and 1.9%, respectively, whereas these rates were 4.0%, 3.4%, and 3.2%, respectively, in non-Hispanic Black women and 3.5%, 2.9%, and 3.2%, respectively, in AIAN women. Maternal height was inversely associated with rates of SGA and positively associated with rates of LGA, which was consistent across all race and ethnicity groups. Composite maternal morbidity rates were elevated (>1.37%) in AIAN women, regardless of maternal stature (Table S4). In particular, AIAN women had elevated rates of transfusion (0.7%–0.8%), compared with other race and ethnicity groups (eg, 0.4%–0.3% in non-Hispanic Whites). Asian women had elevated rates of perineal trauma per 100 vaginal deliveries (2.3 in short women, 2.5 in average-stature women, and 1.8 in tall Asian women).
Figure 1.
Rates of adverse perinatal and maternal outcomes by maternal stature
The graph shows the rates of adverse perinatal (A) and maternal (B) outcomes by maternal stature in women with singleton births in the United States in 2016–2017. The asterisk symbol indicates rates per 100 total births (other rates are per 100 live births). SNM includes ventilation for more than 6 hours, neonatal seizures, and 5-minute Apgar score of ≤3. Composite maternal morbidity includes eclampsia, ICU admission, blood transfusion, uterine rupture, and unplanned hysterectomy. SGA has been defined as a birthweight of <10th percentile.
LGA, large for gestational age; ICU, intensive care unit; NICU, neonatal intensive care unit; PTB, preterm birth; SGA, small for gestational age; SNM, severe neonatal morbidity.
Yearwood. Maternal height and adverse birth outcomes. Am J Obstet Gynecol Glob Rep 2023.
Adjusted results
On average, short women had increased odds of adverse outcomes compared with average-stature women; for example, the adjusted odds of perinatal death in short women were 1.14-fold higher (adjusted odds ratio [AOR], 1.14; 95% confidence interval [CI], 1.10–1.17), and the adjusted odds of composite perinatal death or severe neonatal morbidity in short women were 1.21-fold higher (AOR, 1.21; 95% CI, 1.19–1.23) (Table 3).
Table 3.
AORs and ARDs for adverse birth outcomes in women with singleton births in the United States, 2016–2017
| Perinatal deatha |
Death or severe neonatal morbiditya,b |
Preterm birth at <37 wk of gestation |
|||||
|---|---|---|---|---|---|---|---|
| Fetal and infant outcomes | AOR | ARD | AOR | ARD | AOR | ARD | |
| Short | All | 1.14 (1.10–1.17) | 0.08 (0.06–0.10) | 1.21 (1.19–1.23) | 0.31 (0.28–0.35) | 1.26 (1.25–1.27) | 1.79 (1.72–1.86) |
| Tall | All | 0.99 (0.95–1.03) | 0.00 (−0.03 to 0.02) | 0.89 (0.87–0.91) | −0.13 (−0.17 to −0.08) | 0.83 (0.82–0.85) | −1.13 (−1.20 to −1.06) |
| Short | Non-Hispanic White | 1.26 (1.19–1.33) | 0.14 (0.10–0.18) | 1.28 (1.24–1.33) | 0.53 (0.46–0.61) | 1.39 (1.37–1.42) | 2.47 (2.34–2.60) |
| Non-Hispanic Black | 1.10 (1.03–1.17)c | 0.13 (0.05–0.21) | 1.22 (1.16–1.27) | 0.60 (0.46–0.74) | 1.27 (1.24–1.30)§ | 2.41 (2.17–2.66) | |
| AIAN | 1.09 (0.79–1.49) | 0.13 (−0.17 to 0.43) | 1.28 (1.05–1.56) | 0.79 (0.23–1.35) | 1.29 (1.16–1.42) | 2.45 (1.48–3.42) | |
| Asian | 1.20 (1.09–1.33) | 0.10 (0.04–0.15) | 1.31 (1.23–1.39) | 0.38 (0.28–0.48)c | 1.27 (1.24–1.31)d | 1.78 (1.58–1.98)d | |
| Hispanic | 1.05 (1.00–1.10)d | 0.03 (0.00–0.06)d | 1.10 (1.06–1.13)d | 0.12 (0.07–0.18)c | 1.16 (1.14–1.18)d | 1.14 (1.03–1.25)d | |
| Tall | Non-Hispanic White | 0.95 (0.91–1.00) | −0.02 (−0.04 to 0.01) | 0.90 (0.88–0.93) | −0.15 (−0.20 to −0.10) | 0.82 (0.81–0.83) | −1.14 (−1.22 to −1.06) |
| Non-Hispanic Black | 1.00 (0.93–1.07) | −0.01 (−0.09 to 0.06) | 0.87 (0.82–0.91) | −0.24 (−0.36 to −0.11) | 0.88 (0.85–0.90)§ | −1.09 (−1.30 to −0.88) | |
| AIAN | 0.98 (0.70–1.37) | 0.00 (−0.29 to 0.28) | 1.12 (0.91–1.38) | 0.18 (−0.35 to 0.71) | 0.89 (0.79–0.99) | −1.14 (−1.98 to −0.30) | |
| Asian | 1.32 (0.99–1.78)c | 0.14 (−0.04 to 0.31) | 0.91 (0.72–1.14) | −0.11 (−0.40 to 0.18) | 0.89 (0.81–0.98) | −0.49 (−1.05 to 0.06)c | |
| Hispanic | 1.27 (1.12–1.44)d | 0.16 (0.07–0.25)c | 1.09 (1.01–1.18)d | 0.19 (0.05–0.34)c | 0.87 (0.83–0.91)c | −0.94 (−1.21 to −0.68) | |
Average stature is the reference category adjusted for race, maternal age, parity, body mass index, prenatal care, maternal education, fetal sex, congenital anomalies, chronic diabetes mellitus, chronic hypertension, and type of healthcare insurance (models for perinatal deaths were not adjusted for type of health insurance; this information was not collected on fetal death certificates). The ARD indicates 100 live births (among women with baseline characteristics, ie, no additional risk factor).
AIAN, American Indian or Alaska Native; AOR, adjusted odds ratio; ARD, adjusted risk difference.
All births (preterm birth includes live births only)
Ventilation for more than 6 hours, neonatal seizures, and 5-minute Apgar score of ≤3
Significantly different association compared with the association among non-Hispanic White women (ie, effect modification; P<.05)
Significantly different association compared with the association among non-Hispanic White women (ie, effect modification; P<.0001).
Yearwood. Maternal height and adverse birth outcomes. Am J Obstet Gynecol Glob Rep 2023.
Compared with the ARD of average-stature women, the ARDs of short-stature and average-stature women were relatively small for rare outcomes (3.1 cases of perinatal death or severe neonatal morbidity per 1000 short-stature vs average-stature women). Short women had an additional 17.9 PTBs per 1000 compared with average-stature women (Table 3). In contrast, tall women had lower odds of PTB and composite perinatal death or severe neonatal morbidity, although the risk differences were generally small: 13.1 less PTBs occurred in 1000 tall vs average-stature women (Table 3).
Compared with adjusted associations among non-Hispanic White women, significant differences were observed in the adjusted associations among other race and ethnicity groups. Similarly, short women had higher rates of primary outcomes than average-stature women, although these associations were attenuated in Hispanic vs non-Hispanic White women. Compared with non-Hispanic White women, the associations were weaker for perinatal death and PTB in non-Hispanic Black women and PTB in Asian women. The AORs for short women in these racial and ethnic groups, compared with the average-stature women of their respective race and ethnicity, were lower than the AORs for the short vs average comparisons among non-Hispanic White women (Table 3). For instance, among non-Hispanic Black women, the association between short stature and perinatal death was attenuated (ie, weaker, but statistically significant; a 1.10-fold increase in short non-Hispanic Black women compared with a 1.26-fold increase in short non-Hispanic White women; AORs: 1.10 [95% CI, 1.03–1.17] vs 1.26 [95% CI, 1.19–1.33], respectively). The largest ARDs between short- and average-stature women were observed in PTB among non-Hispanic White, non-Hispanic Black, and AIAN women (ARD, 2.4%–2.5%) (Table 3).
Tall maternal stature was associated with lower adjusted odds of adverse outcomes. Tall non-Hispanic White women had an 18% lower adjusted odds of PTB (AOR, 0.82; 95% CI, 0.81–0.83), a 5% lower adjusted odds of perinatal death (AOR, 0.95; 95% CI, 0.91–1.00), and a 10% lower adjusted odds of composite perinatal death or severe neonatal morbidity (AOR, 0.90; 95% CI, 0.88–0.93) than average-stature non-Hispanic White women (Table 3). These associations were weaker for PTB and perinatal death in tall Hispanic women, for PTB in tall non-Hispanic Black women, and for perinatal death and severe morbidity in AIAN women. Unexpectedly, tall Hispanic women had 27% increased odds of perinatal death compared with average-stature Hispanic women (AOR, 1.27; 95% CI, 1.12–1.44) (Table 3). ARDs in perinatal death and perinatal death or severe neonatal morbidity between tall- and average-stature women were <0.5% and not statistically significant in most race and ethnicity groups. Tall Hispanic women had 1.6 per 1000 more cases of perinatal deaths and 1.9 per 1000 cases of perinatal death or severe neonatal morbidity than average-stature Hispanic women, which was the opposite of what was observed in non-Hispanic White women. There was approximately 1 per 100 less PTBs in tall women of all race and ethnicity groups except for tall Asian women, whose adjusted PTB rates were not significantly different from average-stature Asian women (Table 3).
In the adjusted analyses, modeling maternal height as a continuous variable, a decreasing risk of perinatal death with increasing maternal height was observed in non-Hispanic White women (Figure 2, A). The decline in the predicted probability of death or severe neonatal morbidity as maternal height increased was apparent predominantly in non-Hispanic White and Non-Hispanic Black women (Figure 2, B). There was a clear trend of decreasing the predicted probability of PTB as height increased from 132 to 198 cm among non-Hispanic Black, non-Hispanic White, Asian, and Hispanic women (Figure 2, C).
Figure 2.
Predicted probability of adverse outcomes by maternal height and race and ethnicity
The spline graphs show the predicted probability of perinatal death (A), perinatal death and morbidity (B), and preterm birth at <37 weeks of gestation (C). The predicted probabilities are conditional on average value for other covariates, such as body mass index, having high school of higher education, having prenatal care, not being diagnosed with chronic diabetes mellitus or hypertension, no diagnosed congenital anomalies, and private healthcare insurance.
Yearwood. Maternal height and adverse birth outcomes. Am J Obstet Gynecol Glob Rep 2023.
Comment
Principal findings
In this study of singleton births in the United States, short women had a higher risk of adverse birth outcomes, including PTB at <37 weeks of gestation, perinatal death, and composite perinatal death or severe neonatal morbidity, whereas tall women had a lower risk of all adverse outcomes, except for perinatal death, compared with average-stature women independent of other risk factors, including maternal age, parity, BMI, and education. Furthermore, short-stature mothers had increased rates of composite maternal morbidity, SGA infants, PTB at <34 weeks of gestation, and NICU admissions for their infants, whereas tall-stature mothers had higher rates of LGA and macrosomic infants. The magnitude of these associations varied, and some associations were significantly weaker or stronger in some racial and ethnic groups than in non-Hispanic Whites. For example, the relative risk of perinatal death among short-stature non-Hispanic Black and Hispanic women was smaller than the same relative risk among non-Hispanic White women. Absolute differences in the risk of adverse outcomes were <1% for perinatal death and perinatal death or severe neonatal morbidity; short-statured women had 1.0 to 2.5 more cases of PTBs per 100 compared with average-stature women, depending on race and ethnicity. Except for Asians, tall women had approximately 1 case of PTB per 100 less compared with average-stature women.
Clinical implications
This study comprehensively assessed the association between maternal height and adverse perinatal and maternal health outcomes. Moreover, the quantification of racial and ethnic differences in these associations adds new information to the current literature. Our findings were consistent with previous reports showing that short maternal stature is a risk factor for gestational diabetes mellitus, cephalopelvic disproportion, cesarean delivery, PTB, and FGR.5, 6, 7, 8, 9, 10, 11 Previous studies from Ontario, Canada, and Sweden have reported that short-stature women have an increased risk of PTB and low birthweight5, 6, 7, 8, 9, 10, 11 and that the risk of delivering a low birthweight infant decreased by approximately one-half among tall women.5 Increasing maternal height was associated with decreasing risk of cesarean delivery and child mortality under the age of 5 years.8,20
Racial disparities in adverse birth outcomes have been well described.12, 13, 14,17 However, the differential effects of maternal height have not been examined to date. In this regard, we show that some associations, adjusted for potential confounders, with maternal height are weaker in Hispanic, non-Hispanic Black, and Asian women of short stature (compared with the same associations among non-Hispanic White women). Among tall Asian and Hispanic women, the favorable effect of tall stature is reversed, and tall women in these racial and ethnic groups have an increased risk of perinatal death compared with average-stature women.
Several explanations can be postulated to explain these findings. First, anatomic factors in short-stature mothers can lead to biomechanical constraints during labor and delivery, resulting in adverse birth outcomes.5,10,14,17 Second, above-average height can be an indicator of long-standing good health and proper nutrition as it is influenced by intrauterine, childhood, and environmental factors, in addition to genetic predisposition.9,10 This is, for example, reflected in the concept of the developmental origins of health and disease (DOHaD), which draws on the hypothesis that environmental influences during fetal development could lead to long-term health consequences.25,26 DOHaD infers that below-average maternal stature can occur as a consequence of poor in utero environment and childhood nutritional deficiencies that can consequently increase the risk of adverse birth outcomes in the next generation.7,9,10,27 Third, the increased risk of adverse birth outcomes in short mothers can result from genetic or other familial factors that affect attained height during childhood and adolescence, particularly in some race and ethnic minorities. For example, environmental and genetic factors can influence the early onset of menarche, which is associated with a 2.6 times higher risk of developing a short stature.28,29 Early onset of menarche has been associated with adverse outcomes, including PTB, ectopic pregnancies, miscarriage, and low birthweight.30, 31, 32, 33 Absolute differences in the rates of adverse birth outcomes by maternal stature were not large, and racial or ethnic variation in the risk differences does not warrant different approaches to pregnancy care. However, the effect of maternal stature was more evident in non-Hispanic White women, which is clinically relevant for the standpoint of prognosis. The small increase in perinatal mortality and perinatal mortality or severe neonatal morbidity in tall Hispanic women (compared with average-stature Hispanic women) is somewhat counterintuitive and may be due to differences in nativity. A relatively large proportion of Hispanic women are foreign born, compared with other race groups.34 Foreign-born Hispanic mothers are possibly less likely to be tall (compared with US-born Hispanic mothers), but they may be otherwise “healthy immigrants” who include a smaller proportion who smoke and drink alcohol during pregnancy than their US-born counterparts.35 Thus, unmeasured confounding and a “healthy immigrant” bias may be responsible for the unexpected positive association between tall stature and perinatal death in Hispanic women.
Strengths and limitations
This study has several strengths, including its large size, which enabled the study of rare adverse outcomes, especially in the smaller racial and ethnic groups. The population-based character minimized bias because of selective participation. In addition, the data included detailed information about maternal, obstetrical, and infant characteristics, which were collected consistently throughout the study.
Our study has a few limitations. First, we did not have information on socioeconomic status (SES), which is associated with both race and ethnicity and adverse perinatal outcomes and potentially also with maternal height. Even though we adjusted for education and the type of healthcare insurance, which can be a proxy for SES, our results could have been affected by residual confounding. Moreover, we did not have information about alcohol use during pregnancy. Second, systemic and institutional racism was not addressed in this study, and such factors can have negative health effects because of unequal access to medical care, reduced quality of care, psychosocial stressors, environmental exposures, intergenerational transmission of poverty, and related factors.10,36, 37, 38 These factors were not captured in our data, which could also lead to residual confounding. Third, we contrasted short and tall maternal stature defined using the 10th and 90th percentiles of the overall height distribution. These arbitrary cutoffs were aimed at contrasting the extremes of the height distribution. Previous studies used other cutoffs (eg, 20th and 80th percentiles) with similar, although attenuated, results.6 However, we addressed the continuous nature of height by modeling it in the regression models using splines. Fourth, we did not have geographic information about the place of birth, and therefore, we were not able to account for possible state- or hospital-level clustering. Finally, the racial and ethnic categories used within this study were relatively broad and may not have been homogeneous concerning social and environmental factors that influence adverse birth outcomes. We did not have information about maternal nativity, which may be associated with both maternal height and adverse birth outcomes and vary across racial and ethnic groups.
Conclusion
Our study has added new information to the literature on the effects of maternal height on various perinatal and maternal outcomes. Moreover, our study has addressed the role of race and ethnicity in modifying these associations. Such information can inform healthcare providers about the relationship between maternal height and adverse birth outcomes and help quantify variations in risks specific to each racial and ethnic group. The absolute risk differences in rare adverse events (eg, perinatal death) were low and did not vary substantially by maternal stature. Compared with average-stature women, short women had a higher risk of PTB (by 10–25 cases per 1000) depending on race and ethnicity, and tall women had a lower risk (by 5–10 cases per 1000). Further studies are needed to identify the biologic and sociocultural mechanisms underlying the associations between height and adverse pregnancy outcomes.
Footnotes
The authors report no conflict of interest.
Patient consent is not required because no personal information or detail is included.
This study was supported by funding from the Canadian Institutes of Health Research (CIHR; grant number SKF-154852). L.Y. was supported by the CIHR graduate scholarship. S.L. was supported by a scholar award from the Michael Smith Foundation for Health Research. N.R. was supported by a grant from the Swedish Research Council for Health, Working Life and Welfare (grant number 2019-00041). K.S.J. was supported by an investigator award from the BC Children's Hospital Research Institute.
Data are publicly available at the National Center for Health Statistics (https://www.cdc.gov/nchs/data_access/vitalstatsonline.htm).
This study was based on publicly accessible deidentified data and did not require ethics approval.
Cite this article as: Yearwood L, Bone JN, Wen Q, et al. The association between maternal stature and adverse birth outcomes and the modifying effect of race/ethnicity: a population-based retrospective cohort study. Am J Obstet Gynecol Glob Rep 2023;XX:x.ex–x.ex.
Supplementary material associated with this article can be found in the online version at doi:10.1016/j.xagr.2023.100184.
Appendix. Supplementary materials
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