Maternal mortality in the United States: are the high and rising rates due to changes in obstetrical factors, maternal medical conditions, or maternal mortality surveillance?

BACKGROUND: National Vital Statistics System reports show that maternal mortality rates in the United States have nearly doubled, from 17.4 in 2018 to 32.9 per 100,000 live births in 2021. However, these high and rising rates could reflect issues unrelated to obstetrical factors, such as changes in maternal medical conditions or maternal mortality surveillance (eg, due to introduction of the pregnancy checkbox). OBJECTIVE: This study aimed to assess if the high and rising rates of maternal mortality in the United States reflect changes in obstetrical factors, maternal medical conditions, or maternal mortality surveillance. STUDY DESIGN: The study was based on all deaths in the United States from 1999 to 2021. Maternal deaths were identified using the following 2 approaches: (1) per National Vital Statistics System methodology, as deaths in pregnancy or in the postpartum period, including deaths identified solely because of a positive pregnancy checkbox, and (2) under an alternative formulation, as deaths in pregnancy or in the postpartum period, with at least 1 mention of pregnancy among the multiple causes of death on the death certificate. The frequencies of major cause-of-death categories among deaths of female patients aged 15 to 44 years, maternal deaths, deaths due to obstetrical causes (ie, direct obstetrical deaths), and deaths due to maternal medical conditions aggravated by pregnancy or its management (ie, indirect obstetrical deaths) were quantified. RESULTS: Maternal deaths, per National Vital Statistics System methodology, increased by 144% (95% confidence interval, 130-159) from 9.65 in 1999-2002 (n=1550) to 23.6 per 100,000 live births in 2018-2021 (n=3489), with increases occurring among all race and ethnicity groups. Direct obstetrical deaths increased from 8.41 in 1999-2002 to 14.1 per 100,000 live births in 2018-2021, whereas indirect obstetrical deaths increased from 1.24 to 9.41 per 100,000 live births: 38% of direct obstetrical deaths and 87% of indirect obstetrical deaths in 2018-2021 were identified because of a positive pregnancy checkbox. The pregnancy checkbox was associated with increases in less specific and incidental causes of death. For example, maternal deaths with malignant neoplasms listed as a multiple cause of death increased 46-fold from 0.03 in 1999-2002 to 1.42 per 100,000 live births in 2018-2021. Under the alternative formulation, the maternal mortality rate was 10.2 in 1999-2002 and 10.4 per 100,000 live births in 2018-2021; deaths from direct obstetrical causes decreased from 7.05 to 5.82 per 100,000 live births. Deaths due to preeclampsia, eclampsia, postpartum hemorrhage, puerperal sepsis, venous complications, and embolism decreased, whereas deaths due to adherent placenta, renal and unspecified causes, cardiomyopathy, and preexisting hypertension increased. Maternal mortality increased among non-Hispanic White women and decreased among non-Hispanic Black and Hispanic women. However, rates were disproportionately higher among non-Hispanic Black women, with large disparities evident in several causes of death (eg, cardiomyopathy). CONCLUSION: The high and rising rates of maternal mortality in the United States are a consequence of changes in maternal mortality surveillance, with reliance on the pregnancy checkbox leading to an increase in misclassified maternal deaths. Identifying maternal deaths by requiring mention of pregnancy among the multiple causes of death shows lower, stable maternal mortality rates and declines in maternal deaths from direct obstetrical causes.

Obesity, Twin Pregnancy, and the Role of Assisted Reproductive Technology.

Importance: The prevalence of overweight and obesity (body mass index [BMI] ≥25) has increased globally, and high BMI has been linked to higher rates of twin birth. However, evidence from large population-based studies is lacking; the issue needs careful study, as women with obesity are also more likely to use assisted reproductive technology (ART), which frequently results in twin pregnancy. Objective: To examine the association between BMI and twin birth and the role of ART as a potential mediator in this association. Design, Setting, and Participants: This retrospective cohort study included all live births and stillbirths with gestational age of 20 weeks or longer in British Columbia, Canada, from 2008 to 2020, using data from the British Columbia Perinatal Database Registry. Data analysis was conducted from November 2022 to June 2023. Exposures: Prepregnancy BMI, calculated as weight in kilograms divided by height in meters squared, and use of ART. Main Outcomes and Measures: The study assessed whether prepregnancy BMI is associated with the rate of twin vs singleton delivery and whether this association is explained by the differential use of ART in women with obesity. Results: A total of 524 845 deliveries at 20 weeks' or longer gestation occurred in British Columbia during the study period, and 392 046 women had complete data on prepregnancy BMI. The median (IQR) age was 31.4 (27.7-35.0) years, approximately half were nulliparous (243 443 [46.4%]) and less than 10% smoked during pregnancy (36 894 [7.1%]). Overall, 8295 women had a twin delivery (15.8 per 1000 deliveries), and rates per 1000 deliveries by prepregnancy BMI categories were 11.9 (underweight), 15.1 (normal), 16.0 (overweight), 16.0 (obesity class I), 16.7 (obesity class II), and 18.9 (obesity class III). After adjustment for other covariates, women with underweight had relatively 16% fewer twins compared with women with normal BMI (adjusted risk ratio [aRR], 0.84; 95% CI, 0.74-0.95), while women with overweight, class I obesity, class II obesity, and class III obesity had 14% (aRR, 1.14; 95% CI, 1.07-1.21), 16% (aRR, 1.16; 95% CI, 1.06-1.27), 17% (aRR, 1.17; 95% CI, 1.02-1.34), and 41% higher rates (aRR, 1.41; 95% CI, 1.19-1.66), respectively. The proportion of women who conceived by ART increased with increasing BMI, and ART was associated with nearly a 12-fold higher rate of twin delivery (aRR, 11.80; 95% CI 11.10-12.54). ART explained about a quarter of the association between obesity class I and II and twin delivery (eg, obesity class I, 23% mediated; 95% CI, 7%-39% mediated), but none of this association was mediated by ART in women with class III obesity. Conclusions and relevance: In this cohort study of 524 845 births, the rate of twin birth increased with increasing prepregnancy BMI. In women with a BMI between 30 and 40, approximately one-quarter of this association was explained by higher use of ART; however, there was no evidence of such mediation in women with BMI of 40 or greater.

The clinical performance and population health impact of birthweight-for-gestational age indices at term gestation.

BACKGROUND: The assessment of birthweight for gestational age and the identification of small- and large-for-gestational age (SGA and LGA) infants remain contentious, despite the recent creation of the Intergrowth 21st Project and World Health Organisation (WHO) birthweight-for-gestational age standards. OBJECTIVE: We carried out a study to identify birthweight-for-gestational age cut-offs, and corresponding population-based, Intergrowth 21st and WHO centiles associated with higher risks of adverse neonatal outcomes, and to evaluate their ability to predict serious neonatal morbidity and neonatal mortality (SNMM) at term gestation. METHODS: The study population was based on non-anomalous, singleton live births between 37 and 41 weeks' gestation in the United States from 2003 to 2017. SNMM included 5-min Apgar score <4, neonatal seizures, need for assisted ventilation, and neonatal death. Birthweight-specific SNMM was modelled by gestational week using penalised B-splines. The birthweights at which SNMM odds were minimised (and higher by 10%, 50% and 100%) were estimated, and the corresponding population, Intergrowth 21st, and WHO centiles were identified. The clinical performance and population impact of these cut-offs for predicting SNMM were evaluated. RESULTS: The study included 40,179,663 live births and 991,486 SNMM cases. Among female singletons at 39 weeks' gestation, SNMM odds was lowest at 3203 g birthweight, and 10% higher at 2835 g and 3685 g (population centiles 11th and 82nd, Intergrowth centiles 17th and 88th and WHO centiles 15th and 85th). Birthweight cut-offs were poor predictors of SNMM, for example, the cut-offs associated with 10% and 50% higher odds of SNMM among female singletons at 39 weeks' gestation resulted in a sensitivity, specificity, and population attributable fraction of 12.5%, 89.4%, and 2.1%, and 2.9%, 98.4% and 1.3%, respectively. CONCLUSIONS: Reference- and standard-based birthweight-for-gestational age indices and centiles perform poorly for predicting adverse neonatal outcomes in individual infants, and their associated population impact is also small.

Effect of the COVID-19 Pandemic on Stillbirths in Canada and the United States.

OBJECTIVE: There is uncertainty regarding the effect of the COVID-19 pandemic on population rates of stillbirth. We quantified pandemic-associated changes in stillbirth rates in Canada and the United States. METHODS: We carried out a retrospective study that included all live births and stillbirths in Canada and the United States from 2015 to 2020. The primary analysis was based on all stillbirths and live births at ≥20 weeks gestation. Stillbirth rates were analyzed by month, with March 2020 considered to be the month of pandemic onset. Interrupted time series analyses were used to determine pandemic effects. RESULTS: The study population included 18 475 stillbirths and 2 244 240 live births in Canada and 134 883 stillbirths and 22 963 356 live births in the United States (8.2 and 5.8 stillbirths per 1000 total births, respectively). In Canada, pandemic onset was associated with an increase in stillbirths at ≥20 weeks gestation of 1.01 (95% confidence interval [CI] 0.56-1.46) per 1000 total births and an increase in stillbirths at ≥28 weeks gestation of 0.35 (95% CI 0.16-0.54) per 1000 total births. In the United States, pandemic onset was associated with an increase in stillbirths at ≥20 weeks gestation of 0.48 (95% CI 0.22-0.75) per 1000 total births and an increase in stillbirths at ≥28 weeks gestation of 0.22 (95% CI 0.12-0.32) per 1000 total births. The increase in stillbirths at pandemic onset returned to pre-pandemic levels in subsequent months. CONCLUSION: The COVID-19 pandemic's onset was associated with a transitory increase in stillbirth rates in Canada and the United States.

Obstetric Intervention and Perinatal Outcomes During the Coronavirus Disease 2019 (COVID-19) Pandemic.

OBJECTIVE: To quantify pandemic-related changes in obstetric intervention and perinatal outcomes in the United States. METHODS: We carried out a retrospective study of all live births and fetal deaths in the United States, 2015-2021, with data obtained from the natality, fetal death, and linked live birth-infant death files of the National Center for Health Statistics. Analyses were carried out among all singletons; singletons of patients with prepregnancy diabetes, prepregnancy hypertension, and hypertensive disorders of pregnancy; and twins. Outcomes of interest included preterm birth, preterm labor induction or preterm cesarean delivery, macrosomia, postterm birth, and perinatal death. Interrupted time series analyses were used to estimate changes in the prepandemic period (January 2015-February 2020), at pandemic onset (March 2020), and in the pandemic period (March 2020-December 2021). RESULTS: The study population included 26,604,392 live births and 155,214 stillbirths. The prepandemic period was characterized by temporal increases in preterm birth and preterm labor induction or cesarean delivery rates and temporal reductions in macrosomia, postterm birth, and perinatal mortality. Pandemic onset was associated with absolute decreases in preterm birth (decrease of 0.322/100 live births, 95% CI 0.506-0.139) and preterm labor induction or cesarean delivery (decrease of 0.190/100 live births, 95% CI 0.334-0.047) and absolute increases in macrosomia (increase of 0.046/100 live births), postterm birth (increase of 0.015/100 live births), and perinatal death (increase of 0.501/1,000 total births, 95% CI 0.220-0.783). These changes were larger in subpopulations at high risk (eg, among singletons of patients with prepregnancy diabetes). Among singletons of patients with prepregnancy diabetes, pandemic onset was associated with a decrease in preterm birth (decrease of 1.634/100 live births) and preterm labor induction or cesarean delivery (decrease of 1.521/100 live births) and increases in macrosomia (increase of 0.328/100 live births) and perinatal death (increase of 9.840/1,000 total births, 95% CI 3.933-15.75). Most changes were reversed in the months after pandemic onset. CONCLUSION: The onset of the coronavirus disease 2019 (COVID-19) pandemic was associated with a transient decrease in obstetric intervention (especially preterm labor induction or cesarean delivery) and a transient increase in perinatal mortality.

A flexible approach to modelling stillbirths using the foetuses at risk approach.

BACKGROUND: Survival analysis methods are increasingly used to model the gestational age-specific risk of perinatal phenomena such as stillbirth. OBJECTIVES: To compare two types of survival analysis models, and highlight differences by estimating the relationships between pre-pregnancy BMI and gestational age-specific rates of stillbirth. METHODS: The study was based on singleton live births and stillbirths in the United States in 2016-2017, with data obtained from the natality and fetal death files of the National Center for Health Statistics. We compared Cox regression versus piecewise exponential additive mixed models (PAMMs) for modelling the relationship between BMI and stillbirth across gestational age. In a second analysis, we illustrated the performance of both models for assessing the relationship between the trimester-specific number of cigarettes smoked, a time-dependent covariate, and stillbirth. RESULTS: The study population included 7,567,316 births, of which 42,739 were stillbirths (5.6 per 1000 total births). Stillbirth rates increased with increasing pre-pregnancy BMI and increasing gestational age. In analyses with BMI as a categorical variable, the Cox model and PAMM models yielded similar results. Analyses of BMI as a continuous variable also showed similar results when BMI associations were assumed to be linear, and the changes in gestational age-specific rates were modelled parametrically. However, results differed slightly when PAMMs, modelled with data-driven approaches, were used to estimate changes in BMI effects across gestational age; PAMMs provided a more nuanced modelling of time-varying effects. PAMM models showed an approximately linear increase in the effect of smoking on stillbirth with increasing gestational age. CONCLUSIONS: For survival analyses using the foetuses-at-risk approach, PAMMs provide a valuable alternative to the traditional Cox model, with increased modelling flexibility when proportional hazards assumptions are violated.

Hospital factors associated with maternal and neonatal outcomes of deliveries to patients with a previous cesarean delivery: an ecological study.

BACKGROUND: Recommendations for deliveries of pregnant patients with a previous cesarean delivery and the type of hospitals deemed safe for these deliveries have evolved in recent years, although no studies have examined hospital factors and associated safety. We sought to evaluate maternal and neonatal outcomes among patients with a previous cesarean delivery by hospital tier and volume. METHODS: We carried out an ecological study of singleton live births delivered at term gestation to patients with a previous cesarean delivery in all Canadian hospitals (excluding Quebec), 2013-2019. We obtained data from the Discharge Abstract Database of the Canadian Institute for Health Information. The primary outcomes were severe maternal morbidity or mortality (SMMM), and serious neonatal morbidity or mortality (SNMM). We used regression modelling to examine hospital tier (tier 4 hospitals being those that provide the highest level of care) and volume; we also identified hospitals with high rates of SMMM and SNMM using within-tier comparisons and comparisons with the overall rate. RESULTS: We included 235 442 deliveries to patients with a previous cesarean delivery; SMMM and SNMM rates were 14.6 per 1000 deliveries and 4.6 per 1000 live births, respectively. Among patients with a parity of 1, SMMM rates were lower in tier 1 hospitals (adjusted incidence rate ratio [IRR] 0.68, 95% confidence interval [CI] 0.52-0.89) and higher in tier 4 hospitals (adjusted IRR 1.41, 95% CI 1.05-1.91) than in tier 2 hospitals; SNMM rates did not differ by hospital tier. Rates of SNMM increased with increasing hospital volume (adjusted IRR 1.02, 95% CI 1.00-1.04) and increasing rates of vaginal birth after cesarean delivery (adjusted IRR 1.02, 95% CI 1.01-1.04). Most hospitals had relatively low SMMM and SNMM rates, although a few hospitals in each tier and volume category had significantly higher rates than others. INTERPRETATION: Adverse maternal and neonatal outcomes among patients with a previous cesarean delivery showed no clear pattern of decreasing SMMM and SNMM with increasing tiers of service and hospital volume. All hospitals, irrespective of tier or size, should continually review their rates of adverse maternal and neonatal outcomes.

Racial and Ethnic Disparities in the Perinatal Health of Infants Conceived by ART.

BACKGROUND AND OBJECTIVES: Although racial and ethnic disparities in adverse birth outcomes have been well documented, it is unknown whether such disparities diminish in women who use medically assisted reproduction (MAR). We examined differences in the association between maternal race and ethnicity and adverse birth outcomes among women who conceived spontaneously and those who used MAR, including assisted reproduction technology (ART), eg, in-vitro fertilization, and also non-ART MAR, eg, fertility drugs. METHODS: We conducted a population-based retrospective cohort study using data on all singleton births (N = 7 545 805) in the United States from 2016 to 2017. The outcomes included neonatal and fetal death, preterm birth, and serious neonatal morbidity, among others. Modified Poisson regression was used to estimate adjusted rate ratios (aRR) and 95% confidence intervals (CI) and to assess the interactions between race and ethnicity and mode of conception. RESULTS: Overall, 93 469 (1.3%) singletons were conceived by MAR. Neonatal mortality was twofold higher among infants of non-Hispanic Black versus non-Hispanic White women in the spontaneous-conception group (aRR = 1.9, 95% CI: 1.8-1.9), whereas in the ART-conception group, neonatal mortality was more than fourfold higher in infants of non-Hispanic Black women (aRR = 4.1, 95% CI: 2.9-5.9). Racial and ethnic disparities between Hispanic versus non-Hispanic White women were also significantly larger among women who conceived using MAR with regard to preterm birth (<34 weeks) and perinatal mortality. CONCLUSIONS: Compared to women who conceived spontaneously, racial and ethnic disparities in adverse perinatal outcomes were larger in women who used MAR. More research is needed to identify preventive measures for reducing risks among vulnerable women who use medically assisted reproduction.

Time of delivery among low-risk women at 37-42 weeks of gestation and risks of stillbirth and infant mortality, and long-term neurological morbidity.

BACKGROUND: The most important knowledge gap in connection with obstetric management for time of delivery in term low-risk pregnancies relates to the absence of information on long-term neurodevelopmental outcomes. OBJECTIVES: We examined risks of stillbirth, infant mortality, cerebral palsy (CP) and epilepsy among low-risk pregnancies. METHODS: In this population-based Swedish study, we identified, from 1998 to 2019, 1,773,269 singleton infants born between 37 and 42 completed weeks in women with low-risk pregnancies. Poisson log-linear regression models were used to examine the association between gestational age at delivery and stillbirth, infant mortality, CP and epilepsy. Adjusted rate ratios (RR) and 95% confidence intervals expressing the effect of birth at a particular gestational week compared with birth at a later gestational week were estimated. RESULTS: Compared with those born at a later gestation, RRs for stillbirth and infant mortality were higher among births at 37 weeks' and 38 weeks' gestation. The RRs for infant mortality were approximately 20% and 25% lower among births at 40 or 41 weeks compared with those born at later gestation, respectively. Infants born at 37 and 38 weeks also had higher RRs for CP (vs infants born at ≥38 and ≥39 weeks, respectively), while those born at 39 gestation had similar RRs (vs infants born at ≥40 weeks); infants born at 40 and 41 weeks had lower RRs of CP (vs those born at ≥41 and 42 weeks, respectively). The RRs for epilepsy were higher in those born at 37 and 38 weeks compared with those born at later gestation. CONCLUSIONS: Among low-risk pregnancies, birth at 37 or 38 completed weeks' gestation is associated with increased risks of stillbirth, infant mortality and neurological morbidity, while birth at 39-40 completed weeks is associated with reduced risks compared with births at later gestation.

Maternal and neonatal trauma following operative vaginal delivery.

BACKGROUND: Operative vaginal delivery (OVD) is considered safe if carried out by trained personnel. However, opportunities for training in OVD have declined and, given these shifts in practice, the safety of OVD is unknown. We estimated incidence rates of trauma following OVD in Canada, and quantified variation in trauma rates by instrument, region, level of obstetric care and institutional OVD volume. METHODS: We conducted a cohort study of all singleton, term deliveries in Canada between April 2013 and March 2019, excluding Quebec. Our main outcome measures were maternal trauma (e.g., obstetric anal sphincter injury, high vaginal lacerations) and neonatal trauma (e.g., subgaleal hemorrhage, brachial plexus injury). We calculated adjusted and stabilized rates of trauma using mixed-effects logistic regression. RESULTS: Of 1 326 191 deliveries, 38 500 (2.9%) were attempted forceps deliveries and 110 987 (8.4%) were attempted vacuum deliveries. The maternal trauma rate following forceps delivery was 25.3% (95% confidence interval [CI] 24.8%-25.7%) and the neonatal trauma rate was 9.6 (95% CI 8.6-10.6) per 1000 live births. Maternal and neonatal trauma rates following vacuum delivery were 13.2% (95% CI 13.0%-13.4%) and 9.6 (95% CI 9.0-10.2) per 1000 live births, respectively. Maternal trauma rates remained higher with forceps than with vacuum after adjustment for confounders (adjusted rate ratio 1.70, 95% CI 1.65-1.75) and varied by region, but not by level of obstetric care. INTERPRETATION: In Canada, rates of trauma following OVD are higher than previously reported, irrespective of region, level of obstetric care and volume of OVD among hospitals. These results support a reassessment of OVD safety in Canada.

Maternal Mortality in the United States: Recent Trends, Current Status, and Future Considerations.

Rigorous studies carried out by the National Center for Health Statistics show that previously reported increases in maternal mortality rates in the United States were an artifact of changes in surveillance. The pregnancy checkbox, introduced in the revised 2003 death certificate and implemented by the states in a staggered manner, resulted in increased identification of maternal deaths and in reported maternal mortality rates. This Commentary summarizes the findings of the National Center for Health Statistics reports, describes temporal trends and the current status of maternal mortality in the United States, and discusses future concerns. Although the National Center for Health Statistics studies, based on recoding of death certificate information (after excluding information from the pregnancy checkbox), showed that crude maternal mortality rates did not change significantly between 2002 and 2018, age-adjusted analyses show a temporal reduction in the maternal mortality rate (21% decline, 95% CI 13-28). Specific causes of maternal death, which were not affected by the pregnancy checkbox, such as preeclampsia, showed substantial temporal declines. However, large racial disparities continue to exist: Non-Hispanic Black women had a 2.5-fold higher maternal mortality rate compared with non-Hispanic White women in 2018. This overview of maternal mortality underscores the need for better surveillance and more accurate identification of maternal deaths, improved clinical care, and expanded public health initiatives to address social determinants of health. Challenges with ascertaining maternal deaths notwithstanding, several causes of maternal death (unaffected by surveillance artifacts) show significant temporal declines, even though there remains substantial scope for preventing avoidable maternal death and reducing disparities.