Abstract
Background:
The Institute of Medicine published national recommendations for optimal pregnancy weight gain ranges for singletons and twins, but not higher-order multiples. A common clinical resource suggests weight gain targets for triplet pregnancies, but they are based on a single, small study conducted over 20 years ago.
Objective:
We sought to describe contemporary maternal weight gain patterns in triplet gestations in the U.S., the weight gain patterns associated with good neonatal outcomes, and how these patterns compare to those of healthy twin pregnancies.
Study Design:
We used data from 7705 triplet pregnancies drawn from the US live birth and fetal death files (2012–2018). We calculated total pregnancy weight gain as weight at delivery minus the prepregnancy weight. A good neonatal outcome was defined as delivery at ≥32 weeks’ gestation of 3 liveborn infants weighing ≥1500 g with 5-minute Apgar scores of ≥3. We described the weight gain patterns of triplet pregnancies with good neonatal outcomes by calculating week-specific percentiles of the total weight gain distribution for deliveries at 32 to 37 weeks gestation. For comparative purposes, we plotted these values against the percentiles of a previously-published weight gain chart for monitoring and evaluating twin pregnancies from a referent cohort.
Results:
Most pregnancies were affected by overweight (26%) or obesity (30%), and 42% were normal weight or underweight. The 50th percentile [25th, 75th] of total weight gain in triplet pregnancies was 17 [11, 23] kg. As BMI category increased, total weight gain declined: underweight or normal weight, median 19 [14, 25] kg; overweight, 17 [12, 23] kg; obese, 14 [7.7, 20] kg. Approximately 46% of triplet pregnancies had a good neonatal outcome (n=3562). For underweight or normal weight triplet pregnancies with good neonatal outcomes, the 50th percentile of weight gain at 32 weeks and 36 weeks gestation were 12.3 kg and 22.7 kg, respectively. The 10th and 90th percentiles were 12.3 kg and 32.7 kg at 32 weeks, and 15.0 kg and 34.1 kg at 36 weeks, respectively. Triplet pregnancies with prepregnancy overweight or obesity and a good neonatal outcome had lower weight gains. Compared with reference values for pregnancy weight gain from a twin-specific weight gain chart, the median total weight gain in triplet pregnancies with good neonatal outcomes was approximately 3 to 5 kg more than twins, regardless of BMI.
Conclusions:
Our study fills an important gap in understanding how much weight gain can be expected among triplet pregnancies by BMI category. These descriptive data are a necessary first step to inform science-based triplet gestational weight gain guidelines. Additional research is needed to determine whether monitoring triplet pregnancy weight gain is useful for promoting healthy outcomes for pregnant individuals and children, and what targets should be used to optimize maternal as well as neonatal health.
Keywords: birth certificates, body mass index, multiple pregnancies, neonates, nutrition, pregnancy, triplets, United States, weight gain
Condensation
For normal weight triplet pregnancies with good neonatal outcomes, the 50th percentile [10th, 90th] of weight gain at 32 weeks was 12.3 kg [12.3, 32.7 kg], exceeding gestational weight gain of twin pregnancies for all BMI groups.
Introduction
In 2020, approximately 1 of every 1300 births in the United States was a triplet (1). (2, 3)On average, health care for a triplet pregnancy and the triplets’ first year of life costs $400,000, which is 20-fold higher than that of a singleton pregnancy (4). Triplets die before their first birthday at a rate that is almost 13 times that of singletons (62 per 1000 vs. 5.0 per 1000 births) and 3 times that of twins (22 per 1000 births) (5), primarily due to prematurity and extremely low birthweight (6). (7)Triplet pregnancies are commonly complicated by preeclampsia, gestational diabetes, and hemorrhage (4). In singleton and twin pregnancies, these adverse neonatal health outcomes have been associated with low pregnancy weight gain, and poor outcomes for the pregnant individual are related to high weight gain (8–15). Understanding these links in triplet pregnancies is important because pregnancy weight gain is potentially modifiable.
There is a lack of high-quality evidence to inform the clinical care of triplet pregnancies, including their nutritional care (8, 16–18). The Institute of Medicine (IOM) published national recommendations for optimal pregnancy weight gain ranges for singletons and twins, but not higher-order multiples (8). In the American College of Obstetricians and Gynecologists’ Multifetal Gestations Practice Bulletin, pregnancy weight gain for triplets is not discussed (16). UpToDate, a commonly used clinical resource, suggests two targets for triplet weight gain: the upper limit of the IOM-recommended ranges for twins at term or 0.7 kg per week and >16.2 kg by 24 weeks of gestation (18). This recommendation is based on a single study conducted over 20 years ago of only 192 triplet pregnancies, including fewer than 50 pregnancies affected by overweight or obesity (19). There is little evidence from large, contemporary, population-based studies on the amount of weight US individuals with triplet pregnancies gain, how weight gain differs by BMI category, or the weight gains associated with good pregnancy outcomes in triplet pregnancies.
We sought to describe contemporary maternal weight gain in triplet gestations in the US in each BMI group, and investigated the weight gain patterns associated with good neonatal outcomes in these triplet pregnancies by BMI category. We additionally compared weight gain in triplets with a good outcome to weight gain in twins with a healthy outcome to assess if twin weight gain is a reasonable proxy for triplets. This work is a necessary first step to establishing evidence-based guidelines for triplet pregnancy weight gain.
Materials and Methods
We used data from the US live birth and fetal death files (US Centers for Disease Control and Prevention Division of Vital Statistics http://www.cdc.gov/nchs/data_access/Vitalstatsonline.htm), which include basic demographic, obstetric and neonatal outcome data for 98–99% of births in the US. The study population was drawn from US births and fetal deaths 2012 to 2018. From 2012 to 2016, the number of states adopting the standard birth certificate, which collected data on height and pregnancy weight, increased from 38 (86% of all US births) to 50 (100% of all births) (20). Our ethics board deemed this study review because the data are publicly available and contain no personal identifiers.
The National Center for Health only provides an indicator to identify siblings for twins and higher order multiples from 1995 to 2000 only. We therefore grouped triplet siblings from 2012 to 2018 using a sequential deterministic linkage strategy (21). We first combined the birth and fetal death datasets (with each infant record on its own row) and limited records to those with plurality equal to 3 (n=29,171). We identified 14 variables that should be the same between triplet siblings, including year and month of delivery, parental age, race/ethnicity, education, height, prepregnancy weight, and pregnancy weight gain. Different combinations of at least 6 of these variables plus delivery year were used iteratively over 20 rounds of linkage. Records matched using the most restrictive criteria in round one were removed, and remaining records were matched in a stepwise fashion using progressively less restrictive criteria. Any pregnancy with a mismatch in these 14 variables among infants was reviewed for accuracy on a case-by-case basis. We identified 9296 triplet pregnancies, including 27,888 infants (96% matched; Figure 1).
Figure 1.
Participant flow, United States (2012–2018).
We excluded 146 pregnancies (1.6%) with missing data on gestational age, infant sex, infant birth weight, or 5-minute Apgar score, as well as 369 (4.0%) with a delivery at ≥38 weeks. We used this gestational age cut-point based on professional groups’ practice guidelines for the care of multiple gestations (16, 22). Finally, we removed 900 pregnancies (10%) missing prepregnancy weight, height, or delivery weight. Our final analytic sample was 7705 triplet pregnancies.
Prepregnancy weight and height are ascertained on the birth record via self-report before hospital discharge.(23) We calculated prepregnancy BMI [weight (kg)/ height (m2)], and categorized it as underweight (<18.5 kg/m2), normal weight (18.5–24.9 kg/m2), overweight (25–29.9 kg/m2), or obese (≥30 kg/m2). We combined underweight and normal weight in BMI-stratified analyses due to small counts of underweight individuals.
Data on delivery weight are ascertained on the birth certificate by a hospital staff member, who uses either the last measured weight in the prenatal records or the weight upon admission to labor and delivery (23). We calculated total pregnancy weight gain as weight at delivery minus the prepregnancy weight. To compare triplet weight gain with the only available targets, we calculated the proportion of pregnancies with total weight gain at or above the IOM-recommended upper limit for twins at term (25 kg for underweight and normal weight, 23 kg for overweight, and 19 kg for obese) as well as the proportion with a rate of total weight gain (kg of weight gain/gestational age at delivery) ≥0.7 kg/week (18).
Information on the pregnant person’s race/ethnicity, age, education, marital status, and smoking is obtained through interviews before hospital discharge (23). Best obstetric estimate of gestational age at delivery, route of delivery, infant birth weight, sex, and 5-minute Apgar score are recorded on the birth certificate by the birth attendant (23).
We classified triplet pregnancies as having a good neonatal outcome if they delivered 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more. These cutoffs represent the mean gestational age and birth weight for triplet pregnancies (16, 24, 25). This was our primary outcome. In sensitivity analyses, we also classified pregnancies as having a good maternal and neonatal outcome if they did not have preexisting diabetes, preexisting hypertension, gestational diabetes, or pregnancy-related hypertensive disorders, and met the above definition of good neonatal outcome.
We described the weight gain patterns of triplet pregnancies with good neonatal outcomes by calculating week-specific percentiles of the weight gain distribution (3rd, 10th, 25th, 50th, 75th, 90th, and 97th) for deliveries at 32 to 37 weeks, stratified by BMI category. For comparative purposes, we plotted these values against the percentiles of a previously-published weight gain chart for monitoring and evaluating twin pregnancies from Pittsburgh, PA (26). In sensitivity analyses, we repeated this approach among triplet pregnancies with good maternal and neonatal outcomes.
Results
A majority of individuals with triplet pregnancies in the US were 30–34 years old, non-Hispanic White, college-educated, married, non-smokers, and privately insured (Table 1). The median (interquartile range) gestational age at delivery was 32 (30, 34), and the mean (standard deviation) prepregnancy BMI was 28 (6.9) kg/m2. Most pregnancies were affected by overweight (26%) or obesity (30%), and 42% were normal weight. Compared with underweight and normal weight individuals, individuals with obesity tended to be younger, non-White, high school-educated, unmarried, nulliparous, and did not receive infertility treatment.
Table 1. Characteristics of triplet pregnancies overall and by prepregnancy body mass index, United States 2012 to 2018.
.
| All | Underweight or normal weight | Overweight | Obese | |
|---|---|---|---|---|
| n = 7705 pregnancies, n = 23,115 infants | n = 3439 pregnancies, n = 10,317 infants | n = 1973 pregnancies, n = 5919 infants | n = 2293 pregnancies, n = 6879 infants | |
| Maternal age | ||||
| 25 years or younger | 10 | 9 | 8 | 12 |
| 25 to 29 years | 24 | 24 | 24 | 25 |
| 30 to 34 years | 37 | 38 | 38 | 34 |
| 35 years or older | 29 | 29 | 30 | 29 |
| Maternal race/ethnicity | ||||
| Non-Hispanic White | 64 | 70 | 60 | 59 |
| Non-Hispanic Black | 14 | 9 | 15 | 21 |
| Hispanic | 15 | 12 | 17 | 15 |
| Other | 7 | 9 | 8 | 5 |
| Maternal education | ||||
| High school or less | 22 | 18 | 22 | 29 |
| Some college | 27 | 22 | 29 | 33 |
| Bachelor’s degree | 30 | 34 | 29 | 23 |
| Graduate degree | 21 | 26 | 20 | 15 |
| Married | ||||
| No | 19 | 15 | 19 | 27 |
| Yes | 81 | 85 | 81 | 73 |
| Parity | ||||
| Nulliparous | 23 | 26 | 22 | 20 |
| 1 prior live birth | 27 | 27 | 27 | 25 |
| ≥2 prior live births | 50 | 47 | 51 | 55 |
| Smoked during pregnancy | ||||
| No | 96 | 96 | 97 | 95 |
| Yes | 4 | 4 | 3 | 5 |
| Insurance type | ||||
| Medicaid | 26 | 21 | 26 | 33 |
| Private | 67 | 72 | 65 | 60 |
| Other | 7 | 7 | 9 | 7 |
| Received WIC | ||||
| No | 69 | 76 | 68 | 59 |
| Yes | 31 | 24 | 32 | 41 |
| Received infertility treatment | ||||
| No | 62 | 58 | 63 | 66 |
| Yes | 38 | 42 | 37 | 34 |
| Preexisting hypertension | ||||
| No | 96 | 98 | 97 | 92 |
| Yes | 4 | 2 | 3 | 8 |
| Preexisting diabetes | ||||
| No | 99 | 99 | 99 | 97 |
| Yes | 1 | 1 | 1 | 3 |
| Gestational diabetes | ||||
| No | 89 | 91 | 90 | 85 |
| Yes | 11 | 9 | 10 | 15 |
| Pregnancy-related | ||||
| hypertensive disorders | ||||
| No | 82 | 84 | 83 | 79 |
| Yes | 18 | 16 | 17 | 21 |
| All triplets delivered by | ||||
| cesarean | ||||
| Yes | 94 | 94 | 94 | 93 |
| No | 6 | 6 | 6 | 7 |
| Gestational age, weeks | 32 (30, 34) | 32 (30, 34) | 32 (30, 34) | 32 (30, 34) |
| Gestational age <35 weeks | ||||
| Yes | 81 | 82 | 80 | 81 |
| No | 19 | 18 | 20 | 19 |
| Gestational age <32 weeks | ||||
| Yes | 38 | 38 | 37 | 39 |
| No | 62 | 62 | 63 | 61 |
| Gestational age <28 weeks | ||||
| Yes | 12 | 12 | 12 | 12 |
| No | 88 | 88 | 88 | 88 |
| All triplets were liveborn | ||||
| Yes | 97 | 98 | 97 | 97 |
| No | 3 | 2 | 3 | 3 |
| Infant sex | ||||
| Male | 50 | 50 | 49 | 50 |
| Female | 50 | 50 | 51 | 50 |
| Birthweight, grams | 1695 (1295, 2034) | 1673 (1280, 2013) | 1729 (1304, 2045) | 1701 (1290, 2050) |
| Birthweight <1500 grams | ||||
| Yes | 36 | 38 | 35 | 36 |
| No | 64 | 62 | 65 | 64 |
| 5-minute Apgar score | 9 (8, 9) | 9 (8, 9) | 9 (8, 9) | 9 (8, 9) |
| Congenital anomaly | ||||
| No | 99 | 99 | 100 | 99 |
| Yes | 1 | 1 | 0 | 1 |
| Good neonatal outcome1 | ||||
| No | 54 | 54 | 53 | 54 |
| Yes | 46 | 46 | 47 | 46 |
| Good maternal and neonatal outcome2 | ||||
| No | 68 | 66 | 66 | 72 |
| Yes | 32 | 34 | 34 | 28 |
Good triplet neonatal outcome was defined as delivery of 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more.
Good triplet maternal and neonatal outcome was defined as delivery of 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more in a pregnancy without preexisting diabetes, preexisting hypertension, gestational diabetes, or pregnancy-related hypertensive disorders.
Underweight or normal weight, BMI <25; overweight, BMI 25 to 29; obese, BMI 30 or more kg/m2. WIC, Special Supplemental Nutrition Program for Women, Infants, and Children
Missing data were as follows: education, n = 118; marital status, n = 210; parity, n = 19; smoking, n = 137; insurance, n = 39; WIC, n = 91; infertility treatment, n = 3; preexisting hypertension, n = 3; preexisting diabetes, n = 3; gestational diabetes, n = 3; pregnancy-related hypertensive disorders, n = 3; route of delivery, n = 2.
The median [25th, 75th percentiles] total weight gain in triplet pregnancies was 17 [11, 23] kg. As BMI category increased, total weight gain declined (Figure 2): underweight or normal weight, median 19 [interquartile range 14, 25] kg; overweight, 17 [12, 23] kg; obese, 14 [7.7, 20] kg. The prevalence of weight gain < 5 kg and < 10 kg increased with increasing BMI category: 2% and 10% for underweight or normal weight, 6% and 17% for overweight, and 15 and 33% in obese.
Figure 2.
Distribution of triplet pregnancy weight gain overall and by prepregnancy body mass index, United States (2012–2018).
The box represents the 25th to 75th percentiles of the gestational weight gain distribution, and the line in the box is the median. The whiskers extend to 1.5 times the interquartile range of the lower and upper quartiles. The circles represent the outliers. Weight gain >60 kg and <−10 kg have been removed from the figure. All triplet pregnancies, n=7705; underweight and normal weight, n = 3439; overweight, n = 1973; obese, n = 2293.
In all BMI groups, approximately 46% of triplet pregnancies had a good neonatal outcome (n=3562). The 50th percentile of triplet weight gain in these pregnancies among underweight or normal weight individuals delivering at 32 weeks and 36 weeks were 12.3 kg and 22.7 kg, respectively (Table 2). The 10th and 90th percentiles were 12.3 kg and 32.7 kg at 32 weeks, and 15.0 kg and 34.1 kg at 36 weeks, respectively. In contrast, triplet pregnancies with prepregnancy overweight or obesity and a good neonatal outcome had lower weight gains. For instance, at 32 weeks the 10th, 50th, and 90th percentiles for overweight and obesity were 9.1, 17.7, and 31.4 kg and 5.2, 15.5, and 28.2 kg, respectively.
Table 2. Distribution of pregnancy weight gain among triplet pregnancies with good birth outcomes in the United States (2012–2018) compared with reference values for pregnancy weight gain from a twin pregnancy-specific weight gain chart.
| Total pregnancy weight gain among triplet pregnancies with good neonatal outcomes1 (kg) | Pregnancy weight gain in healthy twin pregnancies2 (kg) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Prepregnancy BMI category | Gestational age (week) | Percentile | Percentile | |||||||||
| n | 3rd | 10th | 50th | 90th | 97th | 3rd | 10th | 50th | 90th | 97th | ||
| Underweight or | 32 | 187 | 8.2 | 12.3 | 21.8 | 32.7 | 35.4 | 7.7 | 10.0 | 15.9 | 23.9 | 28.5 |
| normal weight | 33 | 345 | 9.1 | 13.6 | 22.3 | 31.4 | 36.4 | 8.1 | 10.4 | 16.5 | 24.8 | 29.5 |
| 34 | 490 | 10.0 | 14.1 | 21.4 | 31.4 | 36.8 | 8.5 | 10.9 | 17.2 | 25.8 | 30.7 | |
| 35 | 352 | 8.6 | 14.1 | 22.7 | 31.8 | 35.5 | 9 | 11.4 | 18 | 26.9 | 32.1 | |
| 36 | 155 | 9.1 | 15.0 | 22.7 | 34.1 | 41.8 | 9.4 | 12.0 | 18.9 | 28.2 | 33.6 | |
| 37 | 43 | 10.5 | 15.9 | 22.7 | 30.9 | 34.1 | 9.9 | 12.6 | 19.8 | 29.6 | 35.3 | |
| Overweight | 32 | 121 | 4.1 | 9.1 | 17.7 | 31.4 | 34.5 | 4.4 | 7.0 | 14.3 | 24.8 | 31.1 |
| 33 | 207 | 6.8 | 10.5 | 19.5 | 31.8 | 39.5 | 4.6 | 7.3 | 14.9 | 25.8 | 32.5 | |
| 34 | 251 | 4.5 | 9.1 | 20.0 | 31.8 | 39.1 | 5.0 | 7.7 | 15.6 | 27.0 | 34.0 | |
| 35 | 226 | 6.4 | 10.9 | 20.2 | 31.8 | 37.7 | 5.3 | 8.2 | 16.4 | 28.3 | 35.7 | |
| 36 | 104 | 8.2 | 12.7 | 20.5 | 31.4 | 40.9 | 5.7 | 8.7 | 17.2 | 29.8 | 37.5 | |
| 37 | 28 | 6.4 | 9.5 | 21.4 | 33.6 | 43.2 | 6.0 | 9.2 | 18.1 | 31.3 | 39.5 | |
| Obese | 32 | 130 | 0.0 | 5.2 | 15.5 | 28.2 | 36.4 | 0.1 | 2.7 | 10.4 | 22.4 | 30.2 |
| 33 | 242 | 0.0 | 5.5 | 16.4 | 28.2 | 33.6 | 0.2 | 2.9 | 11.0 | 23.5 | 31.5 | |
| 34 | 290 | −0.91 | 4.8 | 15.5 | 27.7 | 36.4 | 0.5 | 3.3 | 11.7 | 24.8 | 33.3 | |
| 35 | 251 | −0.45 | 5 | 16.8 | 28.2 | 35.9 | 0.8 | 3.7 | 12.5 | 26.3 | 35.3 | |
| 36 | 96 | −2.3 | 3.2 | 18 | 30 | 36.4 | 1.1 | 4.2 | 13.4 | 28.1 | 37.7 | |
| 37 | 44 | −6.8 | 4.1 | 15.7 | 36 | 46.8 | 1.4 | 4.6 | 14.4 | 30.0 | 40.2 | |
Good triplet neonatal outcome was defined as delivery of 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more.
Reference values for pregnancy weight gain from a twin pregnancy-specific weight gain chart in Pittsburgh, Pennsylvania (26).
Compared with reference values for pregnancy weight gain from a twin-specific weight gain chart based on data from a separate US cohort (26), total weight gain in deliveries from 32 to 37 weeks’ in triplet pregnancies with good neonatal outcomes was similar at the 3rd and 10th percentiles, but the 50th, 90th, and 97th percentiles were substantially higher for all BMI groups (Figure 3). For instance, at 34 weeks, the 5th, 10th, 50th, 90th, and 97th percentiles of the pregnancy weight gain distributions for underweight and normal weight individuals were 10, 14.1, 21.4, 31.4, and 36.8 kg among triplets vs. 8.5, 10.9, 17.2, 25.8, and 30.7 kg among twins, respectively (Table 2). Overall, the median total weight gain in triplet pregnancies with good neonatal outcomes was approximately 3 to 5 kg more than twins, regardless of BMI.
Figure 3.
Total maternal weight gain in triplet pregnancies at each week of delivery for pregnancies with a good neonatal outcome* by prepregnancy BMI category, United States (2012–2018).
A good neonatal outcome is defined as delivery of 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more. Panel A: normal weight (n = 1572); Panel B: overweight (n = 937); PaneC: obese (n = 1053).
The results were not meaningfully different when we analyzed triplet pregnancies with good maternal and neonatal outcomes (n=2496; Appendix Figure, Appendix Table).
Comment
Principal Findings
We described the patterns of total pregnancy weight gain among more than 7700 triplet pregnancies in the United States, and found decreasing weight gain as prepregnancy BMI increased. Among triplet pregnancies with good neonatal outcomes, gestational weight gain from 32 to 37 weeks’ gestation was higher and more variable than that of healthy twin pregnancies among all BMI groups.
Results in Context of What is Known
Little is known about gestational weight gain in contemporary cohorts of triplet pregnancies. Published research was conducted 10 to 30 years ago (27–31). In these studies, descriptions of weight gain were limited to means and standard deviations, and pregnancies with overweight and obesity were underrepresented (27–31). In the two studies that sampled 200 or more triplet pregnancies (28, 29), mean total weight gain was similar to our study. A single report of triplet pregnancy weight gain stratified by BMI category reported that mean total weight gain declined as BMI increased (n=116) (31). We are unaware of published work describing gestational age-specific weight gain in healthy triplet pregnancies, either overall or by BMI group. Further, there are no empirical evaluations of triplet versus twin pregnancy weight gain.
Research Implications
With a dearth of descriptive epidemiology on triplet pregnancy weight gain, it is not surprising that the range of weight gain in triplet pregnancies that is optimal for maternal and child health is not known. The generation of evidence-based weight gain guidelines requires understanding the distribution of triplet pregnancy weight gain in the population overall and according to BMI, the patterns of weight gain among healthy triplet pregnancies to set as a standard, and the relation between weight gain and short- and long-term maternal and child health outcomes. Associations between triplet pregnancy weight gain and length of gestation (19, 27, 28, 31), infant birth weight (19, 27–30, 32, 33) and preeclampsia (27, 31, 33) have been reported. However, a majority of these studies have had serious flaws (34), including failing to account for the correlation between weight gain and length of pregnancy (19, 27, 28, 33), control for confounders (19, 27–31), stratify by BMI category (19, 28–30, 33), or consider reverse causality in analyses of preeclampsia (27, 31, 33). Further, outcomes that were key to the development of the Institute of Medicine weight gain recommendations for singletons and twins, including postpartum weight retention, childhood obesity, and infant death (8), have not been studied in triplet pregnancies. In the present work, we have taken a first step to describe the distribution of gestational weight gain in triplet pregnancies overall and by BMI category and describe the pattern of weight gain in triplets with a good outcome. Next steps should include determining the association between weight gain and short and long-term maternal and infant outcomes so clinicians have evidence-based guidelines for triplets.
Clinical Implications
Currently, clinicians have no clear guidance to inform gestational weight gain counseling. In the absence of this guidance, a reasonable option may be to apply twin gestational weight gain guidelines to triplets. However, our data showing higher and more variable weight gain in triplet compared with twin pregnancies suggests this approach is flawed.
Strengths and Limitations
Our study fills an important gap in understanding how much weight gain can be expected among triplet pregnancies by BMI category. Our analysis is not designed to determine optimal ranges of weight gain for triplet pregnancies in these groups. We recognize that some triplets who meet our criteria for a good neonatal outcome may not, in fact, be healthy. Without an accepted definition of a healthy neonatal triplet outcome in the literature or additional data in the birth records, we could not use a more specific definition. Our definition of a good neonatal outcome was based on the mean gestational age and birth weight for triplets, at which survival rates in high-resourced settings is over 95% (35). Furthermore, our approach to classification of a good maternal outcome was limited by imperfect measurement of maternal comorbidities (36, 37) and a lack of data on later-life outcomes strongly related to weight gain in singleton and twin pregnancies (8, 14, 15).
We described triplet pregnancy weight gain compared with that of healthy twin pregnancies from a Pennsylvania-based cohort (26). Optimal pregnancy weight gain in twin gestations is not known (8), and only recently has weight gain been studied in the context of multiple adverse maternal and child health outcomes simultaneously (14, 15). It is therefore possible that, as work in this area expands, a different twin weight gain standard is a more appropriate comparator.
Our cohort excluded a number of triplet pregnancies with missing weight-related data. However, this is unlikely to have introduced selection bias, as the missingness of weight-related data was primarily due to differences in the timing of states’ adoption of the new versions of the standard birth and fetal death certificates that ascertain weight variables, not individual-level characteristics. Without unique identifiers in the dataset, we relied on a deterministic approach to match triplets. However, we are confident that the analytic dataset we used is unlikely to contain inaccurately-linked sibling triplets because deterministic methods are more likely to produce missed-matches as opposed to false matches, as the likelihood of exactly matching on a set of variables and not being a true match is low (38). We have no reason to believe that triplet pregnancies that were missed were systematically different in weight gain or outcomes, and a high proportion of triplets were matched (96%).
Conclusions
The IOM called for more research on healthy pregnancy weight gain for twins and higher-order multiples to fill critical gaps in knowledge that are impeding the development of science-based gestational weight gain guidelines (8). The patterns of weight gain in contemporary US triplet pregnancies described in this study, and the patterns of weight gain associated with good neonatal outcomes, are a critical first step towards the creation of evidence-based recommendations for triplets. Optimizing the nutritional care of triplet pregnancies may prove efficacious in reducing the burden of poor outcomes in this high-risk group.
AJOG at a Glance.
Why was this study conducted? Little is known about patterns of gestational weight gain in contemporary cohorts of triplet pregnancies or the weight gains associated with healthy outcomes. The Institute of Medicine published national recommendations for optimal pregnancy weight gain ranges for singletons and twins, but not higher-order multiples. A common clinical resource suggests weight gain targets for triplet pregnancies, but they are based on a single, small study conducted over 20 years ago.
What are the key findings? For normal weight triplet pregnancies with good neonatal outcomes, the 50th percentile [10th, 90th] of weight gain at 32 weeks was 12.3 kg [12.3, 32.7 kg]. Triplet pregnancies with prepregnancy overweight or obesity and a good neonatal outcome had lower weight gains. These total weight gains exceeded that of twin pregnancies for all BMI groups.
What does this study add to what is already known? These descriptive data are a necessary first step to inform science-based triplet gestational weight gain guidelines.
Sources of support and role of the funding source:
This study is supported by grant funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) R01 HD094777 to Bodnar LM and Hutcheon JA. JAH holds a Canada Research Chair in Perinatal Population Health from the Federal Government of Canada. The study sponsor had no role in the study design; collection, analysis, and interpretation of data; writing the report; or the decision to submit the report for publication.
Appendix Table. Distribution of total pregnancy weight gain among triplet pregnancies with good maternal and neonatal outcomes in the United States (2012–2018).
| Total pregnancy weight gain among triplet pregnancies with good maternal and neonatal outcomes1 (kg) n=2496 | |||||||
|---|---|---|---|---|---|---|---|
| Prepregnancy BMI category | Gestational age (week) | Percentile | |||||
| n | 3rd | 10th | 50th | 90th | 97th | ||
| Underweight or | 32 | 123 | 7.7 | 12.3 | 21.4 | 31.4 | 35 |
| normal weight | 33 | 247 | 9.1 | 13.6 | 22.3 | 30.5 | 35.9 |
| 34 | 360 | 9.5 | 13.9 | 20.9 | 30.9 | 36.4 | |
| 35 | 280 | 9.1 | 13.6 | 22.3 | 31.8 | 35.5 | |
| 36 | 123 | 9.1 | 15.0 | 22.7 | 34.1 | 41.8 | |
| 37 | 38 | 10.5 | 15.0 | 22.7 | 30.9 | 33.6 | |
| Overweight | 32 | 86 | 4.5 | 9.1 | 17.0 | 29.5 | 32.7 |
| 33 | 136 | 6.8 | 10.0 | 18.4 | 29.5 | 38.2 | |
| 34 | 183 | 2.7 | 8.6 | 18.2 | 30.9 | 37.7 | |
| 35 | 171 | 6.8 | 11.4 | 20.5 | 31.8 | 37.3 | |
| 36 | 81 | 4.1 | 12.7 | 21.4 | 31.8 | 45.0 | |
| 37 | 20 | 6.4 | 8.4 | 18.6 | 33.2 | 42.3 | |
| Obese | 32 | 77 | 1.8 | 5.5 | 15.5 | 27.3 | 32.7 |
| 33 | 146 | −1.8 | 4.5 | 15.0 | 28.2 | 33.6 | |
| 34 | 173 | 0.0 | 6.4 | 15.5 | 27.7 | 35.0 | |
| 35 | 156 | −0.45 | 4.5 | 16.8 | 28.2 | 35.5 | |
| 36 | 69 | −2.3 | 2.3 | 16.8 | 27.3 | 33.2 | |
| 37 | 27 | −25.0 | 2.7 | 15.5 | 40.0 | 50.0 | |
A good maternal and neonatal outcome is defined as delivery of 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more in a pregnancy without preexisting diabetes, preexisting hypertension, gestational diabetes, or pregnancy-related hypertensive disorders.
Appendix Figure. Total maternal weight gain in triplet pregnancies at each week of delivery for pregnancies with a good maternal and neonatal outcome by prepregnancy BMI category, United States (2012–2018).
A good maternal and neonatal outcome is defined as delivery of 3 liveborn infants at ≥32 weeks’ gestation, all of whom weighed at least 1500 g and had a 5-minute Apgar scores of 3 or more in a pregnancy without preexisting diabetes, preexisting hypertension, gestational diabetes, or pregnancy-related hypertensive disorders. Panel A: normal weight (n = 1171); Panel B: overweight (n = 677); Panel C: obese (n = 648).
Footnotes
Disclosures: The authors have nothing to disclose.
Data sharing:
Data from the US live birth and fetal death files (US Centers for Disease Control and Prevention Division of Vital Statistics) are available for free online http://www.cdc.gov/nchs/data_access/Vitalstatsonline.htm. Code to replicate our analysis can be found at https://github.com/smparisi/US_Triplets_GWG
References
- 1.Osterman M, Hamilton B, Martin JA, Driscoll AK, Valenzuela CP. Births: Final Data for 2020. Natl Vital Stat Rep 2021. Feb;70(17):1–50. [PubMed] [Google Scholar]
- 2.Martin JA, Osterman MJ, Thoma ME. Declines in Triplet and Higher-order Multiple Births in the United States, 1998–2014. NCHS Data Brief 2016. Apr(243):1–8. [PubMed] [Google Scholar]
- 3.Kamel RM. Assisted reproductive technology after the birth of louise brown. J Reprod Infertil 2013. Jul;14(3):96–109. [PMC free article] [PubMed] [Google Scholar]
- 4.Lemos EV, Zhang D, Van Voorhis BJ, Hu XH. Healthcare expenses associated with multiple vs singleton pregnancies in the United States. Am J Obstet Gynecol 2013. Dec;209(6):586 e1–e11. [DOI] [PubMed] [Google Scholar]
- 5.Ely DM, Driscoll AK. Infant Mortality in the United States, 2017: Data From the Period Linked Birth/Infant Death File. Natl Vital Stat Rep 2019. Aug;68(10):1–20. [PubMed] [Google Scholar]
- 6.Ely DM, Driscoll AK. Infant Mortality in the United States, 2019:Data From the Period Linked Birth/Infant Death File. Natl Vital Stat Rep 2021. Dec;70(14):1–18. [PubMed] [Google Scholar]
- 7.Blickstein I, Keith LG. Outcome of triplets and high-order multiple pregnancies. Curr Opin Obstet Gynecol 2003. Apr;15(2):113–7. [DOI] [PubMed] [Google Scholar]
- 8.Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press; 2009. [PubMed] [Google Scholar]
- 9.Bodnar LM, Himes KP, Abrams B, Parisi SM, Hutcheon JA. Early-pregnancy weight gain and the risk of preeclampsia: A case-cohort study. Pregnancy Hypertens 2018. Oct;14:205–12. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.MacDonald SC, Bodnar LM, Himes KP, Hutcheon JA. Patterns of Gestational Weight Gain in Early Pregnancy and Risk of Gestational Diabetes Mellitus. Epidemiology 2017. May;28(3):419–27. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Goldstein RF, Abell SK, Ranasinha S, Misso M, Boyle JA, Black MH, et al. Association of Gestational Weight Gain With Maternal and Infant Outcomes: A Systematic Review and Meta-analysis. JAMA 2017. Jun 6;317(21):2207–25. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Bodnar LM, Siminerio LL, Himes KP, Hutcheon JA, Lash TL, Parisi SM, et al. Maternal obesity and gestational weight gain are risk factors for infant death. Obesity (Silver Spring) 2015. Nov 17;24(2):490–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Johansson K, Hutcheon JA, Bodnar LM, Cnattingius S, Stephansson O. Pregnancy weight gain by gestational age and stillbirth: a population-based cohort study. BJOG 2018. Jul;125(8):973–81. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Bodnar LM, Cartus AR, Parisi SM, Abrams B, Himes KP, Eckhardt CL, et al. Pregnancy weight gain in twin gestations and maternal and child health outcomes at 5 years. Int J Obes (Lond) 2021. Mar 3. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Bodnar LM, Himes KP, Abrams B, Lash TL, Parisi SM, Eckhardt CL, et al. Gestational Weight Gain and Adverse Birth Outcomes in Twin Pregnancies. Obstet Gynecol 2019. Nov;134(5):1075–86. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies: ACOG Practice Bulletin, Number 231. Obstet Gynecol 2021. Jun 1;137(6):e145–e62. [DOI] [PubMed] [Google Scholar]
- 17.National Institute for Health and Care Excellence. Twin and Triplet Pregnancy NICE Guideline [NG137]. 2019. [cited March 10, 2021]; Available from: https://www.nice.org.uk/guidance/ng137
- 18.Hayes EJ. Triplet pregnancy. UpToDate 2021. [cited March 10, 2021]; Available from: https://www-uptodate-com.pitt.idm.oclc.org/contents/triplet-pregnancy
- 19.Luke B, Nugent C, van de Ven C, Martin D, O’Sullivan MJ, Eardley S, et al. The association between maternal factors and perinatal outcomes in triplet pregnancies. American Journal of Obstetrics & Gynecology 2002. Sep;187(3):752–7. [DOI] [PubMed] [Google Scholar]
- 20.Martin JA, Hamilton BE, Osterman MJK, Driscoll AK, Drake P. Births: Final Data for 2016. Natl Vital Stat Rep 2018. Jan;67(1):1–55. [PubMed] [Google Scholar]
- 21.Bradley CJ, Penberthy L, Devers KJ, Holden DJ. Health services research and data linkages: issues, methods, and directions for the future. Health Serv Res 2010. Oct;45(5 Pt 2):1468–88. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Multiple Pregnancy antenatal care for twin and triplet pregnancies. NICE Clinical Guideline CG 137cvvvvb update. 2019. [cited 2022 April 27]; Available from: https://www.nice.org.uk/guidance/NG137
- 23.CDC National Center for Health Statistics. Birth Edit Specifications for the 2003 Proposed Revision of the U.S. Standard Certificate of Birth http://www.cdc.gov/nchs/data/dvs/birth_edit_specifications.pdf. 2003.
- 24.Battin M, Wise M, DeZoete A, Stone P. Infant and perinatal outcomes of triplet pregnancy in Auckland: better than expected? N Z Med J 2009. Jul 3;122(1298):39–47. [PubMed] [Google Scholar]
- 25.Arlettaz Mieth R, Ersfeld S, Douchet N, Wellmann S, Bucher HU. Higher multiple births in Switzerland: neonatal outcome and evolution over the last 20 years. Swiss Med Wkly 2011;141:w13308. [DOI] [PubMed] [Google Scholar]
- 26.Hutcheon JA, Platt RW, Abrams B, Braxter BJ, Eckhardt CL, Himes KP, et al. Pregnancy Weight Gain by Gestational Age in Women with Uncomplicated Dichorionic Twin Pregnancies. Paediatr Perinat Epidemiol 2018. Jan 29. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Eddib A, Penvose-Yi J, Shelton JA, Yeh J. Triplet gestation outcomes in relation to maternal prepregnancy body mass index and weight gain. Journal of Maternal-Fetal and Neonatal Medicine 2007;20(7):515–9. [DOI] [PubMed] [Google Scholar]
- 28.Elster AD, Bleyl JL, Craven TE. Birth weight standards for triplets under modern obstetric care in the United States, 1984–1989. Obstet Gynecol 1991. Mar;77(3):387–93. [PubMed] [Google Scholar]
- 29.Flidel-Rimon O, Rhea DJ, Shinwell ES, Keith LG, Blickstein I. Early weight gain does not decrease the incidence of low birth weight and small for gestational age triplets in mothers with normal pre-gestational body mass index. Journal of Perinatal Medicine 2006;34(5):404–8. [DOI] [PubMed] [Google Scholar]
- 30.Luke B, Bryan E, Sweetland C, Leurgans S, Keith L. Prenatal weight gain and the birthweight of triplets. Acta Geneticae Medicae et Gemellologiae 1995;44(2):93–101. [DOI] [PubMed] [Google Scholar]
- 31.Shamshirsaz AA, Shamshirsaz AA, Ravangard SF, Allaf MB. Optimal weight gain in triplet pregnancies. J Matern Fetal Neonatal Med 2017. Aug;30(16):1912–5. [DOI] [PubMed] [Google Scholar]
- 32.Flidel-Rimon O, Rhea DJ, Keith LG, Shinwell ES, Blickstein I. Early adequate maternal weight gain is associated with fewer small for gestational age triplets. Journal of Perinatal Medicine 2005;33(5):379–82. [DOI] [PubMed] [Google Scholar]
- 33.Yokoyama Y, Shimizu T. [Optimal maternal weight gain in twin and triplet pregnancy]. Nippon Koshu Eisei Zasshi 1999. Aug;46(8):604–15. [PubMed] [Google Scholar]
- 34.Hutcheon JA, Bodnar LM. Good Practices for Observational Studies of Maternal Weight and Weight Gain in Pregnancy. Paediatr Perinat Epidemiol 2018. Mar;32(2):152–60. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35.Shah PS, Kusuda S, Håkansson S, Reichman B, Lui K, Lehtonen L, et al. Neonatal Outcomes of Very Preterm or Very Low Birth Weight Triplets. Pediatrics 2018;142(6). [DOI] [PubMed] [Google Scholar]
- 36.Gregory ECW, Martin JA, Argov EL, Osterman MJK. Assessing the Quality of Medical and Health Data From the 2003 Birth Certificate Revision: Results From New York City. Natl Vital Stat Rep 2019. Jun;68(8):1–20. [PubMed] [Google Scholar]
- 37.Martin JA, Wilson EC, Osterman MJ, Saadi EW, Sutton SR, Hamilton BE. Assessing the quality of medical and health data from the 2003 birth certificate revision: results from two states. Natl Vital Stat Rep 2013. Jul 22;62(2):1–19. [PubMed] [Google Scholar]
- 38.Grannis SJ, Overhage JM, McDonald CJ. Analysis of identifier performance using a deterministic linkage algorithm. Proc AMIA Symp 2002:305–9. [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Data from the US live birth and fetal death files (US Centers for Disease Control and Prevention Division of Vital Statistics) are available for free online http://www.cdc.gov/nchs/data_access/Vitalstatsonline.htm. Code to replicate our analysis can be found at https://github.com/smparisi/US_Triplets_GWG