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. Author manuscript; available in PMC: 2025 Mar 1.
Published in final edited form as: Am J Obstet Gynecol. 2023 Sep 1;230(3):364.e1–364.e14. doi: 10.1016/j.ajog.2023.08.029

Association between stillbirth and severe maternal morbidity

Samuel H Nyarko a, Lucy T Greenberg b, Ciaran S Phibbs c,d, Jeffrey S Buzas e, Scott A Lorch f,g, Jeannette Rogowski h, George R Saade i, Molly Passarella f, Nansi S Boghossian a,*
PMCID: PMC10904670  NIHMSID: NIHMS1929336  PMID: 37659745

Abstract

Background:

Severe maternal morbidity (SMM) has been increasing in the past few decades. Few studies have examined the risk of SMM among individuals experiencing a stillbirth versus a live birth.

Objective:

To examine the prevalence and risk of SMM among individuals with stillbirth versus individuals with live birth deliveries during delivery hospitalization as a primary outcome and during postpartum period as a secondary outcome.

Study design:

We conducted a retrospective cohort study using birth and fetal death certificate data linked to hospital discharge records from California (2008–2018), Michigan (2008–2020), Missouri (2008–2014), Pennsylvania (2008–2014), and South Carolina (2008–2020). We used relative risk regression analysis to examine the crude and adjusted relative risk (aRR) of SMM along with 95% confidence intervals (CI) among individuals with stillbirth versus live birth deliveries, adjusting for birth year, state of residence, maternal sociodemographic characteristics, and an obstetric comorbidity index.

Results:

Of the 8,694,912 deliveries, 35,012 (0.40%) were stillbirth. Compared to individuals with a live birth delivery, those with a stillbirth were more likely to be non-Hispanic Black (20.5% versus 10.8%), on Medicaid (52.0% versus 46.5%), have pregnancy complications including preexisting diabetes (4.3% versus 1.1%), preexisting hypertension (6.2% versus 2.3%), and preeclampsia (8.4% versus 4.4%), have multiple gestations (6.2% versus 1.6%), and reside in South Carolina (11.6% versus 7.4%). During the delivery hospitalization, the prevalence of SMM for stillbirth versus live birth deliveries was 791 versus 154 cases per 10,000 deliveries, while the prevalence for non-transfusion SMM was 502 versus 68 cases per 10,000 deliveries. The crude RR for SMM was 5.1 (95% CI 4.9–5.3) while the aRR was 1.6 (95% CI 1.5–1.8). For non-transfusion SMM, the crude RR was 7.4 (95% CI 7.0–7.7) while the aRR was 2.0 (95% CI 1.8–2.3) among stillbirth compared with live birth deliveries. This risk was not only elevated among individuals with stillbirth during the delivery hospitalization but also through one year postpartum (SMM aRR: 1.3; 95% CI 1.1–1.4; non-transfusion SMM aRR: 1.2; 95% CI 1.1–1.3).

Conclusion:

Stillbirth was found to be an important contributor to SMM.

Keywords: Stillbirth, severe maternal morbidity, transfusion, acute renal failure, disseminated intravascular coagulation, sepsis, shock, postpartum, obstetric comorbidity index score

Tweetable Statement:

Stillbirth is associated with elevated severe maternal morbidity risk.

Introduction

Severe maternal morbidity (SMM) is the unintended outcome of the process of labor and delivery that causes significant short- or long-term consequences to a woman’s health.1 The rate of SMM has been steadily increasing in recent years in the United States,2,3 making SMM a major health care concern in the country. For instance, between 2012 and 2019, there has been a cumulative increase of 14.7 percent – from 69.5 per 10,000 to 79.7 per 10,000 delivery hospitalizations – in SMM cases excluding blood transfusions during delivery hospitalizations with the most common indicators being disseminated intravascular coagulation, acute kidney failure, hysterectomy, sepsis, and adult respiratory distress syndroome.4 This observed surge in SMM is likely attributable to significant increases in multiple factors including maternal age, obesity, clinical conditions, and pregnancy complications.5,6

While a growing body of research has examined SMM and associated maternal characteristics,7–13 limited studies have examined SMM rates among stillbirths versus live births. Existing research on this topic is limited to two states in the United States.14,15 Thus, these studies may not provide a broader understanding of SMM among individuals who have a stillbirth. About 21,000 stillbirths are recorded annually during delivery hospitalizations in the United States, occurring at a rate of 57.0 fetal deaths per 10,000 live births and fetal deaths.16 In the current study, we performed a multi-state analysis examining the prevalence and relative risk of SMM and its indicators among individuals with stillbirth versus live birth deliveries.

Materials and Methods

Data sources

The study drew on birth and fetal death records linked to maternal delivery hospitalizations, as previously described.17 Data were obtained from California (2008–2018), Michigan (2008–2020), Missouri (2008–2014), Pennsylvania (2008–2014), and South Carolina (2008–2020). For California, Michigan, and South Carolina, data were also available on inpatient hospitalizations during the antenatal period and through 365 days postpartum. We restricted our dataset to births between 22–44 weeks gestational age. We also excluded 331,496 (3.6%) records due to the inability to link the birth or fetal death certificate to the maternal hospital discharge data, 56,833 (0.6%) records without valid gestational age, birth weight, county, hospital, and/or maternal age, and 139,636 (1.5%) records to restrict the sample to the first birth record for birthing individuals with multiple gestations. The final analytical sample size was 8,694,912 comprising 35,012 (0.40%) stillbirths and 8,659,900 (99.6%) live births. The institutional review boards of the University of South Carolina, Children’s Hospital of Philadelphia, and the departments of health in the five respective states approved the study.

Study variables

The primary outcomes of the study were SMM and SMM excluding blood transfusions (non-transfusion SMM) occurring during the delivery hospitalization.14,15 Secondary outcomes included SMM and non-transfusion SMM occurring during pregnancy or within 42 or 365 days postpartum, which were only available for California, Michigan, and South Carolina. We examined non-transfusion SMM as in previous studies5,18,19 since blood transfusion is the most common indicator of SMM20 and blood transfusion alone is not indicative of the severity of the condition without the number of blood transfused units. We used the Centers for Disease Control and Prevention (CDC) ICD-9 or ICD-10 diagnosis and procedure code algorithm to identify cases of SMM. SMM was defined as the occurrence of 16 life-threatening maternal conditions (such as heart failure, renal failure, sepsis, shock, and sickle cell crisis) and 5 life-saving procedures (such as ventilation, tracheostomy, and blood transfusion).20 The Maternal and Child Health Bureau’s federally available data resource document was used to ensure the appropriate transitioning from the CDC’s ICD-9 to ICD-10 coding system.20,21

Gestational age on the birth certificate was determined using the obstetric estimate when available, and if unavailable using the last menstrual period estimate.

Statistical analysis

We first conducted descriptive analyses examining maternal characteristics by live birth vs. stillbirth status. We examined the prevalence of SMM per 10,000 deliveries by gestational age at delivery and by birth outcome (live birth vs. stillbirth) with 95% confidence intervals (CI). We also computed the prevalence (per 10,000 deliveries) and unadjusted relative risk (RR) of SMM, non-transfusion SMM, and SMM indicators among stillbirths compared with live births. We subsequently used relative risk regression models to estimate the adjusted RR (aRR) and 95% CI for each outcome.22 The fit of the log-binomial model was examined by plotting mean observed versus predicted rates for data grouped by centiles of predicted values. The plots indicated the fit was satisfactory. Models were adjusted for birth year, state of residence, insurance type (private, government, self-pay, other, or missing), educational attainment (no high school, some high school, high school, some college, 4-year college, >4-year college, or missing), race/ethnicity (non-Hispanic White, non-Hispanic Black, Hispanic, non-Hispanic Asian, American Indian, or other/missing), maternal age (quadratic), Adequacy of Prenatal Care Utilization Index (inadequate, intermediate, adequate, adequate plus, or missing),23 and an obstetric comorbidity index, a validated score that includes 27 patient-level risk factors (Supplementary Table 1) for SMM.24 In a separate analysis to compare our results with a previous study,15 we adjusted for preexisting diabetes, preexisting hypertension, preeclampsia, gestational diabetes, and gestational hypertension without adjusting for an obstetric comorbidity index score. We also performed several sensitivity analyses by: 1) limiting the data to deliveries at 31 weeks’ gestation and above, 2) excluding California, and 3) excluding multiple gestations. R statistical software (version 4.1.3) was used to perform all analyses.25

Results

Compared to individuals who had a live birth delivery, individuals who had a stillbirth were more likely to be non-Hispanic black, be a smoker, have Medicaid insurance, have missing educational status, have higher SMM, non-transfusion SMM, and comorbidity index score, and have higher rates of preexisting diabetes, preexisting hypertension, preeclampsia, and multiple gestations. Individuals who had a stillbirth were also more likely to have missing data on adequacy of prenatal care, be obese, and to reside in SC (Table 1). Individuals who had a stillbirth were less likely to have a cesarean delivery compared to those with a live birth delivery.

Table 1.

Maternal characteristics by stillbirth versus live birth deliveries in California, Michigan, Missouri, Pennsylvania, and South Carolina

Characteristics Stillbirth
N= 35,012		 Live birth
N= 8,659,900
Race/Ethnicity
 Non-Hispanic White 13189 (37.7) 3723042 (43.0)
 Non-Hispanic Black 7187 (20.5) 935843 (10.8)
 Hispanic 10763 (30.7) 2872743 (33.2)
 Asian 2691 (7.7) 859952 (9.9)
 American Indian 111 (0.3) 27508 (0.3)
 Other 1071 (3.1) 240812 (2.8)
Age
 <20 3040 (8.7) 620947 (7.2)
 20–24 7539 (21.5) 1828398 (21.1)
 25–34 17221 (49.2) 4721149 (54.5)
 ≥35 7212 (20.6) 1489406 (17.2)
Smoker* 2601 (22.9) 567985 (16.7)
Payor
 Private 13675 (39.1) 4343361 (50.2)
 Medicaid 18215 (52.0) 4024707 (46.5)
 Self-Pay 1097 (3.1) 195334 (2.3)
 Other 264 (0.8) 60027 (0.7)
Education
 No high school 1582 (4.5) 381604 (4.4)
 Some high school 4390 (12.5) 1091514 (12.6)
 High school diploma/GED 8619 (24.6) 2184332 (25.2)
 At least some college 7665 (21.9) 2345034 (27.1)
 4-year college 4039 (11.5) 1546188 (17.9)
 >4-year college 1959 (5.6) 880177 (10.2)
 Missing 6758 (19.3) 231051 (2.7)
Cesarean delivery 6295 (18.0) 2781616 (32.1)
SMM Comorbidity Index Score, median (IQR) 9 (8, 17) 1 (0, 5)
Non-transfusion SMM Comorbidity Index Score, median (IQR) 13 (13, 20) 1 (0, 6)
Preexisting diabetes 1511 (4.3) 93998 (1.1)
Preexisting hypertension 2179 (6.2) 195606 (2.3)
Preeclampsia 2926 (8.4) 382172 (4.4)
Gestational diabetes 2187 (6.2) 670735 (7.7)
Gestational hypertension 971 (2.8) 313247 (3.6)
Multiple gestation 2129 (6.2) 140102 (1.6)
Adequacy of Prenatal Care Utilization Index
 Inadequate 3730 (10.7) 946578 (10.9)
 Intermediate 972 (2.8) 921082 (10.6)
 Adequate 3155 (9.0) 3574406 (41.3)
 Adequate Plus 8866 (25.3) 2911087 (33.6)
 Missing 18289 (52.2) 306747 (3.5)
Obese BMI 7695 (32.5) 1987297 (24.1)
State of Data
 California 19679 (56.2) 5252442 (60.7)
 Michigan 5670 (16.2) 1405162 (16.2)
 Missouri 2043 (5.8) 494478 (5.7)
 Pennsylvania 3571 (10.2) 866155 (10.0)
 South Carolina 4049 (11.6) 641663 (7.4)
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No. (%) unless otherwise indicated.

*

Smoking status missing in California

BMI, Body Mass Index; GED, General Education Development; IQR, Inter-quartile Range.

Figure 1 shows the prevalence and 95% CI of SMM and non-transfusion SMM per 10,000 deliveries by gestational age and stillbirth versus live birth. Unlike deliveries at gestational ages prior to 31 weeks for SMM and 30 weeks for non-transfusion SMM, gestational-age-specific rates of SMM and non-transfusion SMM starting at 31 and 30 weeks of gestation, respectively, were higher among stillbirths compared with live births.

Fig. 1.

Fig. 1

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Prevalence and 95% CI of SMM and non-transfusion SMM per 10,000 deliveries by gestational age and stillbirth versus live birth in California, Michigan, Missouri, Pennsylvania, and South Carolina.

The prevalences of SMM and non-transfusion SMM were higher among individuals who had a stillbirth (791 and 502 per 10,000 deliveries, respectively) versus a live birth (154 and 68 per 10,000 deliveries, respectively) (Table 2). In multivariate analyses and after adjusting for maternal sociodemographic characteristics, the SMM risk was almost four times higher among individuals who had a stillbirth compared with those who had a live birth (transfusion SMM aRR: 3.8; 95% CI: 3.7–3.9; non-transfusion SMM aRR: 5.1; 95% CI: 4.8–5.3). After further adjusting for an obstetric comorbidity index, the SMM risk became attenuated but was still higher among individuals with stillbirth compared with those with live birth deliveries (transfusion SMM aRR: 1.6; 95% CI: 1.5–1.8; non-transfusion SMM aRR: 2.0; 95% CI: 1.8–2.3) (Table 2). Adjusting for maternal sociodemographic characteristics and pregnancy complications (preexisting diabetes, preexisting hypertension, preeclampsia, gestational diabetes, and gestational hypertension) as has been done previously15 instead of an comorbidity index, shows a higher SMM risk for stillbirth compared with live birth deliveries (transfusion SMM aRR: 3.5; 95% CI: 3.3–3.6; non-transfusion SMM aRR: 4.5; 95% CI: 4.3–4.7) (Table 2). The results for all the SMM indicators except for heart failure showed significantly higher risks for individuals with stillbirths versus those with live births (Supplementary Table 2). The model adjusting for an obstetric comorbidity index showed that the risk ratios were highest for disseminated intravascular coagulation (aRR: 4.4; 95% CI: 4.1–4.8), sepsis (aRR: 4.0; 95% CI: 3.5–4.7), shock (aRR: 3.0; 95% CI: 2.5–3.8), and acute renal failure (aRR: 2.9; 95% CI: 2.2–3.8).

Table 2.

Prevalence and relative risk of SMM during the delivery hospitalization among individuals with stillbirth versus live birth deliveries in California, Michigan, Missouri, Pennsylvania, and South Carolina

Characteristics Cases (Cases per 10,000 deliveries) Risk Ratio (95% CI)
Stillbirth
N=35,012		 Live birth
N=8,659,900		 Unadjusted RR Adjusted RRa Adjusted RR including comorbidity indexb Adjusted RR including obstetric factorsc
SMM 2768 (791) 133415 (154) 5.1 (4.9, 5.3) 3.8 (3.7, 3.9) 1.6 (1.5, 1.8) 3.5 (3.3, 3.6)
Non-transfusion SMM 1758 (502) 58989 (68) 7.4 (7.0, 7.7) 5.1 (4.8, 5.3) 2.0 (1.8, 2.3) 4.5 (4.3, 4.7)
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a

Adjusted for: birth year, state, insurance, education, race/ethnicity, maternal age, and prenatal care adequacy.

b

Adjusted for: birth year, state, insurance, education, race/ethnicity, maternal age, prenatal care adequacy, and obstetric comorbidity index.

c

Adjusted for: birth year, state, insurance, education, race/ethnicity, maternal age, prenatal care adequacy, preexisting diabetes, preexisting hypertension, preeclampsia, gestational diabetes, and gestational hypertension.

Table 3 presents the risk ratios of prenatal, delivery, and postpartum SMM among individuals who delivered stillbirths versus those who delivered live births from California, Michigan, and South Carolina. The rates of SMM and non-transfusion SMM were notably highest during delivery hospitalization among both stillbirths and live births although these rates were considerably higher among stillbirths compared with live births (Table 3/Figure 2). At any time during the prenatal, delivery, or 365 days postpartum, the adjusted risk of SMM was 1.6-fold (95% CI: 1.5–1.7) and non-transfusion SMM was 1.7-fold (95% CI: 1.5–1.8) higher among individuals with stillbirth compared with individuals with live births. The adjusted risk ratio for SMM within 365 days postpartum was 1.3 (95% CI: 1.1–1.4) and for non-transfusion SMM it was 1.2 (95% CI: 1.1–1.3). The adjusted risk ratios of SMM indicators were elevated within 365 days postpartum (Supplementary Table 3). The SMM indicators with the highest increased aRR were air and thrombotic embolism (aRR=2.3; 95% CI: 1.8–3.1), disseminated intravascular coagulation (aRR=1.8; 95% CI: 1.3–2.6), and transfusion (aRR=1.7; 95% CI: 1.5–2.1).

Table 3.

Prevalence and relative risk of prenatal, delivery and postpartum SMM among individuals with stillbirth versus live birth deliveries in California, Michigan, and South Carolina

Characteristics Cases (Cases per 10,000 deliveries) Risk Ratio (95% CI)
Stillbirths
N=29,398		 Live births
N=7,299,238		 Unadjusted RR Adjusted RRa Adjusted RR including comorbidity indexb Adjusted RR including obstetric factorsc
SMM
 During delivery hospitalization 2387 (812) 117367 (161) 5.1 (4.9, 5.3) 3.7 (3.6, 3.9) 1.6 (1.4, 1.8) 3.4 (3.3, 3.6)
 At any time during pregnancy, delivery, or within 42 days postpartum 2644 (899) 148481 (203) 4.4 (4.3, 4.6) 3.3 (3.2, 3.4) 1.6 (1.5, 1.7) 3.0 (2.9, 3.1)
 At any time during pregnancy, delivery, or within 365 days postpartum 2822 (960) 166222 (228) 4.2 (4.1, 4.4) 3.1 (3.0, 3.2) 1.6 (1.5, 1.7) 2.9 (2.7, 3.0)
 During pregnancy 175 (60) 16538 (23) 2.6 (2.3, 3.0) 1.8 (1.5, 2.1) 0.9 (0.8, 1.1) 1.5 (1.3, 1.8)
 Post-discharge within 42 days postpartum 204 (69) 19599 (27) 2.6 (2.3, 3.0) 1.9 (1.7, 2.2) 1.2 (1.0, 1.3) 1.8 (1.5, 2.0)
 Post-discharge within 365 days postpartum 459 (156) 39691 (54) 2.9 (2.6, 3.1) 2.1 (1.9, 2.3) 1.3 (1.1, 1.4) 1.9 (1.7, 2.1)
Non-transfusion SMM
 During delivery hospitalization 1478 (503) 50274 (69) 7.4 (7.0, 7.7) 5.0 (4.7, 5.3) 2.0 (1.7, 2.3) 4.4 (4.2, 4.7)
 At any time during pregnancy, delivery, or within 42 days postpartum 1707 (581) 77123 (106) 5.5 (5.2, 5.8) 3.9 (3.7, 4.1) 1.7 (1.6, 1.9) 3.4 (3.3, 3.6)
 At any time during pregnancy, delivery, or within 365 days postpartum 1864 (634) 92650 (127) 5.0 (4.8, 5.2) 3.5 (3.4, 3.7) 1.7 (1.5, 1.8) 3.1 (3.0, 3.3)
 During pregnancy 142 (48) 13563 (19) 2.6 (2.2, 3.1) 1.8 (1.5, 2.1) 0.9 (0.8, 1.1) 1.5 (1.3, 1.8)
 Post-discharge within 42 days postpartum 176 (60) 16417 (22) 2.7 (2.3, 3.1) 2.0 (1.7, 2.3) 1.2 (1.0, 1.4) 1.8 (1.5, 2.1)
 Post-discharge within 365 days postpartum 378 (129) 33628 (46) 2.8 (2.5, 3.1) 2.0 (1.8, 2.2) 1.2 (1.1, 1.3) 1.8 (1.6, 1.9)
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a

Adjusted for: birth year, state, insurance, education, race/ethnicity, maternal age, and prenatal care adequacy.

b

Adjusted for: birth year, state, insurance, education, race/ethnicity, maternal age, prenatal care adequacy, and obstetric comorbidity index.

c

Adjusted for: birth year, state, insurance, education, race/ethnicity, maternal age, prenatal care adequacy, preexisting diabetes, preexisting hypertension, preeclampsia, gestational diabetes, and gestational hypertension.

Fig. 2.

Fig. 2

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Prevalence of SMM and non-transfusion SMM per 10,000 deliveries by timing of SMM and stillbirth versus live birth in California, Michigan, and South Carolina.

Given that the main differences in the rate of SMM among individuals with stillbirth versus live birth deliveries occurred starting at 31 weeks’ gestation, we reran the analyses for the primary outcome restricting the dataset to individuals with deliveries ≥31 weeks. The results did not change direction, but the adjusted RRs were slightly higher (SMM aRR: 2.0; 95% CI: 1.7–2.3; non-transfusion SMM aRR: 2.6; 95% CI: 2.1–3.1) than among the total sample which included individuals with deliveries from 22 to 44 weeks gestational age (Supplementary Table 4). Similarly, in the sensitivity analysis excluding California data (SMM aRR: 1.8; 95% CI: 1.6–2.0; non-transfusion SMM aRR: 2.3; 95% CI: 2.0–2.6) (Supplementary Table 5) and multiple gestations (SMM aRR: 1.7; 95% CI: 1.5–1.9; non-transfusion SMM aRR: 2.2; 95% CI: 1.9–2.4) (Supplementary Table 6), the adjusted RRs only increased slightly than among the total sample and retained the same direction.

Comment

Principal findings

In a population-based study from 5 states, we found that about 1 in 13 and 1 in 20 individuals who had a stillbirth delivery experienced SMM and non-transfusion SMM, respectively. We also found that after adjusting for maternal sociodemographic characteristics and an comorbidity index, the risk ratio of SMM and non-transfusion SMM was about 2-fold (95% CI: 1.8–2.1) and 2.5-fold (95% CI: 2.2–2.8), respectively, for individuals who had a stillbirth compared with those who had a live birth delivery. The SMM indicators with the highest adjusted risk ratios among stillbirth versus live birth deliveries included acute renal failure, disseminated intravascular coagulation, sepsis, and shock. These risk ratios were not only elevated among individuals with stillbirth during the delivery hospitalization but also during the prenatal period and through one year postpartum.

Results in the context of what is known

Previous population-based SMM studies have either combined stillbirth and live birth deliveries,5,7 controlled for stillbirth deliveries26 or excluded stillbirth deliveries.11 Very few studies have examined SMM among individuals with stillbirth versus live birth deliveries. In a California study among 6,459,842 deliveries, Wall-Wieler and colleagues reported more than 4-fold (95% CI: 4.53–5.02) and 5-fold (95% CI: 5.11–5.88) higher risk ratios of SMM and non-transfusion SMM, respectively, among stillbirth compared with live birth deliveries after adjusting for maternal sociodemographic characteristics and pregnancy complications.15 In another study conducted in Florida and stratified by the presence (n=420,064) and absence of comorbidities (n=942,503), Lewkowitz and colleagues reported that individuals with stillbirth deliveries had increased odds of SMM (with comorbidities adjusted odds ratio (aOR): 6.21; 95% CI: 5.54–6.96; without comorbidities aOR: 7.05; 95% CI: 6.27–7.93) and non-transfusion SMM (with comorbidities aOR: 5.04; 95% CI: 4.22–6.02; without comorbidities aOR: 6.50; 95% CI: 5.19–8.12) compared with individuals with live birth deliveries after adjusting for maternal sociodemographic characteristics and mode of delivery.14 In a retrospective cohort study examining factors associated with SMM during the delivery hospitalization, Chen and colleagues showed that individuals with stillbirth compared to those with live birth deliveries, had higher odds of SMM; aOR of 4.66 (95% CI: 4.29–5.07) and 3.80 (95% CI: 3.53–4.10) in the Medicaid and commercial insurance cohorts, respectively.7 In a study of 1,892,857 singleton births in Ontario, Canada, mothers with SMM compared to those without SMM were reported to have over 6-fold (95% CI: 5.69–6.81) higher risk of stillbirth.27

There are several reasons for these higher associations in prior studies compared to ours. We used a more detailed obstetric comorbidity index that is a validated index comprising 27 patient-level risk factors for SMM that have been scored and ranked in terms of importance.24 Some of these obstetric comorbidity indicators are risk factors for both SMM and stillbirth deliveries, which may explain the attenuated results in our study once we adjusted for an obstetric comorbidity index. SMM and stillbirth share multiple risk factors including advanced age, overweight/obesity, multiple gestations, and preexisting medical conditions such as preeclampsia, diabetes mellitus, and hypertension, all of which are also included in an obstetric comorbidity index.12,28–36 The differences in the study populations may also explain the variations in the adjusted risk ratios between our study and the previous studies. The proportion of non-Hispanic Black individuals in our sample for example was 11.65% while it was 5.75% in the Wall-Wieler et al. study15 and 21.37% in the Lewkowitz et al study.14 Non-Hispanic black individuals are known to have higher rates of SMM18,31 and stillbirth deliveries34,36 compared to individuals of other racial/ethnic groups.

The findings of the current study further showed that the SMM risks may extend beyond the delivery admission period through 365 days postpartum. While it is hard to discern whether the SMM that occurs beyond 42 days postpartum is pregnancy related, this indicates that these individuals may continue to be at heightened risk for adverse outcomes in the postpartum period. A previous study of 7,398,640 births in California between 1999 and 2011, showed that individuals who had a stillbirth had 1.47 times (95% CI: 1.35–1.60) higher risk of readmission at 6 weeks postpartum compared to those who had a live birth.37 In another California study examining patient-level risk factors for postpartum hospital readmission among 29,654 individuals with a stillbirth from 1997 to 2011, those who had non-transfusion SMM and those with transfusion only during the delivery hospitalization were more likely to have a readmission within 6 weeks postpartum (non-transfusion SMM aOR: 3.02; 95% CI: 2.28–4.00; transfusion only aOR: 1.95; 95% CI: 1.35–2.81).38 Other risk factors for postpartum readmission among individuals with a stillbirth delivery included pregnancy complications, antenatal hospitalization, cesarean delivery, non-Hispanic Black race, and having less than a high school education.38

We observed that unlike deliveries occurring before 31 weeks of gestation for SMM and before 30 weeks for non-transfusion SMM, the gestational-age-specific rates of both SMM and non-transfusion SMM, were higher among stillbirths than live births starting at 31 and 30 weeks of gestation, respectively. Our finding that the disparity in SMM rate is more likely to exist at later gestational ages mirror the findings of the Wall-Wieler et al. study.15 One of the possible reasons for the lack of disparities in SMM rates in the earlier gestational ages may be due to potential misclassification of short-lived live births as stillbirths.39,40 Variations may also exist in the definition of stillbirths and short-lived live births among health care providers or state registries leading to possible misclassification.40 Finally, the phenotype of both stillbirths and live births in the earlier gestational period may overlap and result in lack of difference in SMM.41

Clinical implications

Our study suggests that pregnant individuals who have a stillbirth have a higher risk for SMM at any time during pregnancy, the delivery hospitalization, and through one year postpartum. With individual SMM indicators including acute renal failure, disseminated intravascular coagulation, sepsis, and shock posing the highest risks of morbidity among this group of individuals, it may be essential for health care providers to prioritize monitoring individuals with a stillbirth delivery. Additionally, critically monitoring the underlying risk factors of these high-risk SMM indicators can help to mitigate their incidence.

Research implications

Data on cause of fetal death and future research that better characterizes the causes of fetal death that are most predictive of SMM are needed. Additionally, it is critical to understand whether quality of outpatient care can mitigate SMM risk among individuals experiencing a fetal death.

Strength and limitations

The main strength of this study is the large sample size of linked hospital administrative, fetal death and live birth records and inclusion of several states. Also, unlike previous studies, by including a more detailed obstetric comorbidity index, we accounted for a wide range of clinical risk factors for SMM. Nevertheless, there are also some limitations to consider. First, findings from this retrospective cohort study cannot infer causality between stillbirth and severe maternal morbidity. Second, certain live births might have been misclassified as stillbirths especially at earlier gestational ages.39,40 Third, for certain maternal characteristics such as maternal education and adequacy of prenatal care utilization, we had more missing data for stillbirths than live births. We treated the missing data as a separate category in the statistical analysis. Fourth, we did not have cause of fetal death to explore in more depth whether risk of SMM differed by the cause of fetal death. A previous study showed that the prevalence of SMM varied considerably by cause of fetal death ranging from 1 per 100 deliveries for causes resulting from major structural malformations or genetic abnormalities to 24 per 100 deliveries for hypertensive disorders.15 Lastly, the ICD codes for SMM and the indicators in the obstetric comorbidity index might be subject to misclassifications.

Conclusions

Our findings indicate that stillbirth delivery is associated with elevated risk of SMM and its indicators not only during the delivery hospitalization but also at any time during the prenatal period, and up to one year postpartum.

Supplementary Material

1
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2
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3

AJOG at a Glance:

Why was this study conducted?

  • Few studies have examined the association between stillbirth and severe maternal morbidity.

  • This study examined the association between stillbirth and severe maternal morbidity.

Key findings

  • The prevalence and risk of severe maternal morbidity and its indicators were more elevated among individuals with stillbirth than those with live birth deliveries after adjusting for maternal sociodemographic and clinical factors.

What does this study add to what is known?

  • In a multi-state population level study, the risks of severe maternal morbidity were higher among individuals who have a stillbirth compared to a live birth delivery at any time during pregnancy, delivery, and through one year postpartum.

Acknowledgements

  • The data used in this document/presentation was acquired from the Michigan Department of Health and Human Services (MDHHS) and the Missouri Department of Health and Senior Services (DHSS). The contents of this document including data analysis, interpretation or conclusions are solely the responsibility of the authors and do not represent the official views of MDHHS or DHSS.

  • This information is from the records of the revenue and fiscal affairs office, health and demographics section, South Carolina. Our authorization to release this information does not imply endorsement of this study or its findings by either the revenue and fiscal affairs office or the data oversight council.

Funding

Supported by the National Institute on Minority Health and Health Disparities under Award Number R01MD016012.

Role of funder/sponsor

The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The National Institutes of Health had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Footnotes

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Disclosure

The authors report no conflict of interest.

Disclaimer

The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs or the U.S. government.

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