Linked birth cohort files for perinatal health research: California as a model for methodology and implementation

Socioeconomic disadvantage and racial/ethnic disparities in low-risk cesarean birth in California

Our objective was to assess the relationship of socioeconomic disadvantage and race/ethnicity with low-risk cesarean birth. We examined birth certificates (2007-2018) linked with maternal hospitalization data from California; the outcome was cesarean birth among low-risk deliveries (ie, nulliparous, term, singleton, vertex [NTSV]). We used generalized estimation equation Poisson regression with an interaction term for race/ethnicity (n = 7 groups) and a measure of socioeconomic disadvantage (census tract-level neighborhood deprivation index, education, or insurance). Among 1 815 933 NTSV births, 26.6% were by cesarean section. When assessing the joint effect of race/ethnicity and socioeconomic disadvantage among low-risk births, risk of cesarean birth increased with socioeconomic disadvantage for most racial/ethnic groups, and disadvantaged Black individuals had the highest risks. For example, Black individuals with a high school education or less had a risk ratio of 1.49 (95% CI, 1.45-1.53) relative to White individuals with a college degree. The disparity in risk of cesarean birth between Black and White individuals was observed across all strata of socioeconomic disadvantage. Asian American and Hispanic individuals had higher risks than White individuals at lower socioeconomic disadvantage; this disparity was not observed at higher levels of disadvantage. Black individuals have a persistent, elevated risk of cesarean birth relative to White individuals, regardless of socioeconomic disadvantage.

Racial and Ethnic Disparities in Cervical Insufficiency, Cervical Cerclage, and Preterm Birth

Background: The frequency of cervical insufficiency differs among the major racial and ethnic groups, with limited data specific to Asian American and Native Hawaiian/Pacific Islander (AANHPI) subpopulations. We assessed cervical insufficiency diagnoses and related outcomes across 10 racial and ethnic groups, including disaggregated AANHPI subgroups, in a large population-based cohort. Study Design: We performed a retrospective cohort study of all singleton births between 20-42 weeks' gestation in California from 2007 to 2018. Logistic regression models were performed to estimate the odds of cervical insufficiency and, among people with cervical insufficiency, the odds of cerclage and preterm birth according to self-reported race and ethnicity. Results: Among 5,114,470 births, 38,605 (0.8%) had a diagnosis code for cervical insufficiency. Compared with non-Hispanic White people, non-Hispanic Black people had the highest odds of cervical insufficiency (adjusted odds ratio [aOR] 3.07; 95% confidence interval [CI], 2.97, 3.18), for cerclage placement and higher odds for preterm birth. Disaggregating AANHPI subgroups showed that Indian people had the highest odds (aOR 1.94; 95% CI, 1.82, 2.07) of cervical insufficiency and had significantly higher odds of cerclage without increased odds of preterm birth; Southeast Asian people had the highest odds of preterm birth. Conclusion: Within a large, diverse population-based cohort, non-Hispanic Black people experienced the highest rates of cervical insufficiency, and among those with cervical insufficiency, had among the highest rates of cerclage and preterm birth. Among AANHPI subgroups specifically, Indian people had the highest rates of cervical insufficiency and cerclage placement, without increased rates of preterm birth; Southeast Asian people had the highest rates of preterm birth, without increased rates of cerclage. Disaggregating AANHPI subgroups identifies important differences in obstetric risk factors and outcomes.

Individual-, Hospital-, and Community-Level Factors Associated with Sudden Unexpected Infant Death Among Infants Born Preterm in 5 US States

OBJECTIVE

To investigate individual-, hospital-, and community-level factors associated with sudden unexpected infant death (SUID) among infants born preterm.

STUDY DESIGN

The following linked dataset from 5 states (California, Michigan, Oregon, Pennsylvania, and South Carolina) from 2005 through 2020 was used: (1) infant birth and death certificates; (2) maternal and infant birth hospitalization discharge records; (3) birthing hospital data from the American Hospital Association; and (4) community-level data from the Social Vulnerability Index (SVI).) Multivariable models were used to assess the independent association between these multilevel factors and SUID, adjusting for several maternal and infant characteristics.

RESULTS

Overall, we found that maternal demographic factors (race and ethnicity, education, insurance) and infant gestational age were significant predictors of SUID. There was no difference in SUID odds by state, urban influence code, and maternal complications of pregnancy. Compared with mothers who lived in areas with the lowest SVI, those who resided in the highest SVI were more likely to experience SUID. There was no difference in SUID odds between infants who did or did not experience one or more complications of prematurity. For hospital-level factors, there was no difference in SUID odds among infants cared for in teaching vs nonteaching hospitals or in low vs high volume preterm birth hospitals.

CONCLUSION

Individual- and community-level factors were associated with SUID among infants born preterm. The neonatal intensive care unit hospitalization may provide a critical window of opportunity to engage families about SUID-risk reducing practices.

Severe Maternal Morbidity and Other Perinatal Complications Among Black, Hispanic, and White Birthing Persons With and Without Physical Disabilities

Background: People with physical disabilities are at increased risk of adverse perinatal outcomes, including severe maternal morbidity (SMM). Risks may be even greater for disabled people in minoritized racial or ethnic groups, but little is known about this intersection. Methods: We analyzed linked hospital discharge and vital records data from California, 2008-2020. We identified physical disabilities using diagnosis codes for maternal congenital anomalies, major injuries, musculoskeletal disorders, or nervous system disorders. We compared birthing persons in five groups (Black and Hispanic with and without physical disabilities, White with physical disabilities) to a reference group of non-Hispanic Whites without disabilities. We used Poisson regression to assess associations with SMM and other outcomes, with and without adjusting for sociodemographic and clinical covariates. Results: Disabled Black and Hispanic birthing persons had particularly high relative risks (RRs) of SMM (Black disabled RR = 6.13, 95% confidence interval [CI]: 4.94, 7.61; Hispanic disabled RR = 3.67, 95% CI: 3.29, 4.10) as compared with nondisabled White persons. These risks were greater than those for nondisabled Black (RR = 2.05, 95% CI: 1.99, 2.11), nondisabled Hispanic (RR = 1.36, 95% CI: 1.34, 1.39), and disabled White birthing persons (RR = 2.44, 95% CI: 2.16, 2.77). For most other outcomes, risks were also largest for disabled Black birthing persons, followed by disabled Hispanic birthing persons. Conclusions: Black and Hispanic people with physical disabilities are highly likely to experience SMM and are at increased risk for other complications and adverse outcomes. Efforts are needed to understand underlying causes of these disparities and develop policies and practices to eliminate them.

Magnesium sulfate and risk of hypoxic-ischemic encephalopathy in a high-risk cohort

BACKGROUND

Hypoxic-ischemic encephalopathy contributes to morbidity and mortality among neonates ≥36 weeks of gestation. Evidence of preventative antenatal treatment is limited. Magnesium sulfate has neuroprotective properties among preterm fetuses. Hypertensive disorders of pregnancy are a risk factor for hypoxic-ischemic encephalopathy, and magnesium sulfate is recommended for maternal seizure prophylaxis among patients with preeclampsia with severe features.

OBJECTIVE

(1) Determine trends in the incidence of hypertensive disorders of pregnancy, antenatal magnesium sulfate, and hypoxic-ischemic encephalopathy; (2) evaluate the association between hypertensive disorders of pregnancy and hypoxic-ischemic encephalopathy; and (3) evaluate if, among patients with hypertensive disorders of pregnancy, the odds of hypoxic-ischemic encephalopathy is mitigated by receipt of antenatal magnesium sulfate.

STUDY DESIGN

We analyzed a prospective cohort of live births ≥36 weeks of gestation between 2012 and 2018 within the California Perinatal Quality Care Collaborative registry, linked with the California Department of Health Care Access and Information files. We used Cochran-Armitage tests to assess trends in hypertensive disorders, encephalopathy diagnoses, and magnesium sulfate utilization and compared demographic factors between patients with or without hypertensive disorders of pregnancy or treatment with magnesium sulfate. Hierarchical logistic regression models were built to explore if hypertensive disorders of pregnancy were associated with any severity and moderate/severe hypoxic-ischemic encephalopathy. Separate hierarchical logistic regression models were built among those with hypertensive disorders of pregnancy to evaluate the association of magnesium sulfate with hypoxic-ischemic encephalopathy.

RESULTS

Among 44,314 unique infants, the diagnosis of hypoxic-ischemic encephalopathy, maternal hypertensive disorders of pregnancy, and the use of magnesium sulfate increased over time. Compared with patients with hypertensive disorders of pregnancy alone, patients with hypertensive disorders treated with magnesium sulfate represented a high-risk population. They were more likely to be publicly insured, born between 36 and 38 weeks of gestation, be small for gestational age, have lower Apgar scores, require a higher level of resuscitation at delivery, have prolonged rupture of membranes, experience preterm labor and fetal distress, and undergo operative delivery (all P<.002). Hypertensive disorders of pregnancy were associated with hypoxic-ischemic encephalopathy (adjusted odds ratio, 1.26 [95% confidence interval, 1.13-1.40]; P<.001) and specifically moderate/severe hypoxic-ischemic encephalopathy (adjusted odds ratio, 1.26 [95% confidence interval, 1.11-1.42]; P<.001). Among patients with hypertensive disorders of pregnancy, treatment with magnesium sulfate was associated with 29% reduction in the odds of neonatal hypoxic-ischemic encephalopathy (adjusted odds ratio, 0.71 [95% confidence interval, 0.52-0.97]; P=.03) and a 37% reduction in the odds of moderate/severe neonatal hypoxic-ischemic encephalopathy (adjusted odds ratio, 0.63 [95% confidence interval, 0.42-0.94]; P=.03).

CONCLUSION

Hypertensive disorders of pregnancy are associated with hypoxic-ischemic encephalopathy and, specifically, moderate/severe disease. Among people with hypertensive disorders, receipt of antenatal magnesium sulfate is associated with a significant reduction in the odds of hypoxic-ischemic encephalopathy and moderate/severe disease in a neonatal cohort admitted to neonatal intensive care unit at ≥36 weeks of gestation. The findings of this observational study cannot prove causality and are intended to generate hypotheses for future clinical trials on magnesium sulfate in term infants.

Are Racial and Ethnic Disparities in Brachial Plexus Birth Injuries Explained by Known Risk Factors?

Objective

To investigate the association of maternal race/ethnicity with risk factors for brachial plexus birth injury (BPBI) and quantify the proportion of excess BPBI risk due to these factors.

Study design

This retrospective cohort study of all livebirths occurring in California-licensed hospitals from 1996-2012 included 6,278,562 maternal-livebirth infant pairs with 7,762 BPBI diagnoses. Multiple logistic regression and causal mediation analyses were used to evaluate the relationship of race/ethnicity and BPBI risk factors.

Results

Black and Hispanic birthing-individuals were at increased risk of obesity, diabetes, and limited prenatal care utilization but decreased risk of many BPBI risk factors (shoulder dystocia, macrosomia, prolonged second stage of labor, and vaginal delivery).

Conclusions

Black and Hispanic birthing-individuals were at lower risk of many strongly associated risk factors for BPBI, and these factors mediate only a small proportion of their excess BPBI risk, underscoring the importance of identifying alternative risk factors, especially drivers of demographic disparities.

Hypertensive Disorders in Pregnancy: Differences by Hispanic Ethnicity and Black Race

OBJECTIVE

Black individuals carry the greatest burden of maternal mortality, with hypertensive disorders during pregnancy being a significant driving force to this disparity. However, research on maternal health disparities predominantly groups Hispanic Black individuals with all other individuals of Hispanic ethnicity. We hypothesized that this aggregation might obscure the risk patterns of hypertensive disorders in pregnancy for Hispanic-Black and non-Hispanic Black individuals.

METHODS

We analyzed a California statewide dataset of vital records linked to hospitalization discharge data for births from 2007 to 2018. Using multivariable logistic regression models adjusted for age, pre-pregnancy BMI, parity, smoking status, diabetes, and chronic renal disease, we compared the odds of hypertensive disorders in pregnancy between Hispanic Black, non-Hispanic Black, and non-Black Hispanic racial-ethnic groups. Hypertensive disorders were categorized into two groups: (1) any hypertensive disorder and (2) chronic hypertension alone, non-severe hypertensive disorders, and severe hypertensive disorders in pregnancy.

RESULTS

Non-Hispanic Black people had 75% increased odds of developing a hypertensive disorder during pregnancy (adjusted odds ratio (aOR); 95% confidence interval (CI): 1.74, 1.78) and Hispanic-Black individuals had a 31% increased odds (95% CI: 1.24, 1.38) as compared with non-Black Hispanic individuals. When considering hypertensive disorders separately, the race-associated differences were largest for chronic hypertension alone, with non-Hispanic Black individuals showing an aOR of 2.35 (95% CI: 2.32, 2.38) and Hispanic-Black individuals an aOR of 1.80 (95% CI: 1.66, 1.95).

CONCLUSION

Compared with non-Black Hispanic individuals, the prevalence of hypertensive disorders in pregnancy was higher in Black-Hispanic individuals and highest in non-Hispanic Black individuals. Racial/ethnic differences were larger for chronic hypertension alone than for preeclampsia.

A Counterfactual Analysis of Impact of Cesarean Birth in a First Birth on Severe Maternal Morbidity in the Subsequent Birth

BACKGROUND

It is known that cesarean birth affects maternal outcomes in subsequent pregnancies, but specific effect estimates are lacking. We sought to quantify the effect of cesarean birth reduction among nulliparous, term, singleton, vertex (NTSV) births (i.e., preventable cesarean births) on severe maternal morbidity (SMM) in the second birth.

METHODS

We examined birth certificates linked with maternal hospitalization data (2007-2019) from California for NTSV births with a second birth (N = 779,382). The exposure was cesarean delivery in the first birth and the outcome was SMM in the second birth. We used adjusted Poisson regression models to calculate risk ratios and population attributable fraction for SMM in the second birth and conducted a counterfactual impact analysis to estimate how lowering NTSV cesarean births could reduce SMM in the second birth.

RESULTS

The adjusted risk ratio for SMM in the second birth given a prior cesarean birth was 1.7 (95% confidence interval: 1.5, 1.9); 15.5% (95% confidence interval: 15.3%, 15.7%) of this SMM may be attributable to prior cesarean birth. In a counterfactual analysis where 12% of the California population was least likely to get a cesarean birth instead delivered vaginally, we observed 174 fewer SMM events in a population of individuals with a low-risk first birth and subsequent birth.

CONCLUSION

In our counterfactual analysis, lowering primary cesarean birth among an NTSV population was associated with fewer downstream SMM events in subsequent births and overall. Additionally, our findings reflect the importance of considering the cumulative accrual of risks across the reproductive life course.

Considering pregnancies as repeated vs independent events: an empirical comparison of common approaches across selected perinatal outcomes

BACKGROUND

In population-based research, pregnancy may be a repeated event. Despite published guidance on how to address repeated pregnancies to the same individual, a variety of approaches are observed in perinatal epidemiological studies. While some of these approaches are supported by the chosen research question, others are consequences of constraints inherent to a given dataset (eg, missing parity information). These decisions determine how appropriately a given research question can be answered and overall generalizability.

OBJECTIVE

To compare common cohort selection and analytic approaches used for perinatal epidemiological research by assessing the prevalence of two perinatal outcomes and their association with a clinical and a social independent variable.

STUDY DESIGN

Using vital records linked to maternal hospital discharge records for singleton births, we created four cohorts: (1) all-births (2) randomly selected one birth per individual (3) first-observed birth per individual (4) primiparous-births (parity 1). Sampling of births was not conditional on cluster (ie, we did not sample all births by a given mother, but rather sampled individual births). Study outcomes were severe maternal morbidity (SMM) and preeclampsia/eclampsia, and the independent variables were self-reported race/ethnicity (as a social factor) and systemic lupus erythematosus. Comparing the four cohorts, we assessed the distribution of maternal characteristics, the prevalence of outcomes, overall and stratified by parity, and risk ratios (RR) for the associations of outcomes with independent variables. Among all-births, we then compared RR from three analytic strategies: with standard inference that assumes independently sampled births to the same mother in the model, with cluster-robust inference, and adjusting for parity.

RESULTS

We observed minor differences in the population characteristics between the all-birth (N=2736,693), random-selection, and first-observed birth cohorts (both N=2284,660), with more substantial differences between these cohorts and the primiparous-births cohort (N=1054,684). Outcome prevalence was consistently lowest among all-births and highest among primiparous-births (eg, SMM 18.9 per 1000 births among primiparous-births vs 16.6 per 1000 births among all-births). When stratified by parity, outcome prevalence was always the lowest in births of parity 2 and highest among births of parity 1 for both outcomes. RR differed for study outcomes across all four cohorts, with the most pronounced differences between the primiparous-birth cohort and other cohorts. Among all-births, robust inference minimally impacted the confidence bounds of estimates, compared to the standard inference, that is, crude estimates (eg, lupus-SMM association: 4.01, 95% confidence intervals [CI] 3.54-4.55 vs 4.01, 95% CI 3.53-4.56 for crude estimate), while adjusting for parity slightly shifted estimates, toward the null for SMM and away from the null for preeclampsia/eclampsia.

CONCLUSION

Researchers should consider the alignment between the methods they use, their sampling strategy, and their research question. This could include refining the research question to better match inference possible for available data, considering alternative data sources, and appropriately noting data limitations and resulting bias, as well as the generalizability of findings. If parity is an established effect modifier, stratified results should be presented.

Readmission After Neonatal Intensive Care Unit Discharge: The Importance of Social Drivers of Health

OBJECTIVE

To determine associations between sociodemographic and medical factors and odds of readmission after discharge from the neonatal intensive care unit for infants with very low birth weight (<1500g).

STUDY DESIGN

Cohort study using linked data from the California Perinatal Quality Care Collaborative, California Vital Statistics, and the Child Opportunity Index (COI) 2.0. Infants with very low birth weight born from 2009 through 2018 in California were considered. Odds ratios of readmission within 30 days of discharge adjusting for infant medical factors, maternal sociodemographic factors, and birth hospital were calculated via multivariable logistic regression and fixed-effect logistic regression models.

RESULTS

A total of 42 411 infants met inclusion criteria. Also, 8.5% of all infants were readmitted within 30 days of discharge. In addition to traditional medical risk factors, two sociodemographic factors were significantly associated with increased odds of readmission in adjusted models: payor other than private insurance for delivery [aOR = 1.25 (95% CI 1.14-1.36)] and maternal education of less than high school degree [aOR = 1.19 (95% CI 1.06-1.33)]. Neighborhood Child Opportunity Index was not associated with odds of readmission.

CONCLUSIONS

Sociodemographic factors, including lack of private insurance and lower maternal educational attainment, are significantly and independently associated with increased odds of readmission after neonatal intensive care unit discharge, in addition to traditional medical risk factors. Socioeconomic deprivation and health literacy may contribute to risk of readmission. Targeted discharge interventions focused on addressing social drivers of health warrant exploration.

Variation in Hospital Neuraxial Labor Analgesia Rates in California

BACKGROUND

Neuraxial analgesia provides effective pain relief during labor. However, it is unclear whether neuraxial analgesia prevalence differs across U.S. hospitals. The aim of this study was to assess hospital variation in neuraxial analgesia prevalence in California.

METHODS

A retrospective cross-sectional study analyzed birthing patients who underwent labor in 200 California hospitals from 2016 to 2020. The primary exposure was the delivery hospital. The outcomes were hospital neuraxial analgesia prevalence and between-hospital variability, before and after adjustment for patient and hospital factors. Median odds ratio and intraclass correlation coefficients quantified between-hospital variability. The median odds ratio estimated the odds of a patient receiving neuraxial analgesia when moving between hospitals. The intraclass correlation coefficients quantified the proportion of the total variance in neuraxial analgesia use due to variation between hospitals.

RESULTS

Among 1,510,750 patients who underwent labor, 1,040,483 (68.9%) received neuraxial analgesia. Both unadjusted and adjusted hospital prevalence exhibited a skewed distribution characterized by a long left tail. The unadjusted and adjusted prevalences were 5.4% and 6.0% at the 1st percentile, 21.0% and 21.2% at the 5th percentile, 70.6% and 70.7% at the 50th percentile, 75.8% and 76.6% at the 95th percentile, and 75.9% and 78.6% at the 99th percentile, respectively. The adjusted median odds ratio (2.3; 95% CI, 2.1 to 2.5) indicated substantially increased odds of a patient receiving neuraxial analgesia if they moved from a hospital with a lower odds of neuraxial analgesia to one with higher odds. The hospital explained only a moderate portion of the overall variability in neuraxial analgesia (intraclass correlation coefficient, 19.1%; 95% CI, 18.8 to 20.5%).

CONCLUSIONS

A long left tail in the distribution and wide variation exist in the neuraxial analgesia prevalence across California hospitals that is not explained by patient and hospital factors. Addressing the low prevalence among hospitals in the left tail requires exploration of the interplay between patient preferences, staffing availability, and care providers' attitudes toward neuraxial analgesia.

EDITOR’S PERSPECTIVE

Trends and Disparities in Severe Maternal Morbidity Indicator Categories during Childbirth Hospitalization in California from 1997 to 2017

OBJECTIVE

Severe maternal morbidity (SMM) is increasing and characterized by substantial racial and ethnic disparities. Analyzing trends and disparities across time by etiologic or organ system groups instead of an aggregated index may inform specific, actionable pathways to equitable care. We explored trends and racial and ethnic disparities in seven SMM categories at childbirth hospitalization.

STUDY DESIGN

We analyzed California birth cohort data on all live and stillbirths ≥ 20 weeks' gestation from 1997 to 2017 (n = 10,580,096) using the Centers for Disease Control and Prevention's SMM index. Cases were categorized into seven nonmutually exclusive indicator categories (cardiac, renal, respiratory, hemorrhage, sepsis, other obstetric, and other medical SMM). We compared prevalence and trends in SMM indicator categories overall and by racial and ethnic group using logistic and linear regression.

RESULTS

SMM occurred in 1.16% of births and nontransfusion SMM in 0.54%. Hemorrhage SMM occurred most frequently (27 per 10,000 births), followed by other obstetric (11), respiratory (7), and sepsis, cardiac, and renal SMM (5). Hemorrhage, renal, respiratory, and sepsis SMM increased over time for all racial and ethnic groups. The largest disparities were for Black individuals, including over 3-fold increased odds of other medical SMM. Renal and sepsis morbidity had the largest relative increases over time (717 and 544%). Sepsis and hemorrhage SMM had the largest absolute changes over time (17 per 10,000 increase). Disparities increased over time for respiratory SMM among Black, U.S.-born Hispanic, and non-U.S.-born Hispanic individuals and for sepsis SMM among Asian or Pacific Islander individuals. Disparities decreased over time for sepsis SMM among Black individuals yet remained substantial.

CONCLUSION

Our research further supports the critical need to address SMM and disparities as a significant public health priority in the United States and suggests that examining SMM subgroups may reveal helpful nuance for understanding trends, disparities, and potential needs for intervention.

KEY POINTS

· By SMM subgroup, trends and racial and ethnic disparities varied yet Black individuals consistently had highest rates.. · Hemorrhage, renal, respiratory, and sepsis SMM significantly increased over time.. · Disparities increased for respiratory SMM among Black, U.S.-born Hispanic and non-U.S.-born Hispanic individuals and for sepsis SMM among Asian or Pacific Islander individuals..

Quality, outcome, and cost of care provided to very low birth weight infants in California

OBJECTIVE

To examine association of costs with quality of care and patient outcome across hospitals in California.

METHODS

Retrospective study of very low birth weight (VLBW) births from 2014-2018 linking birth certificate, hospital discharge records and clinical data. Quality was measured using the Baby-MONITOR score. Clinical outcome was measured using survival without major morbidity (SWMM). Hierarchical generalized linear models, adjusting for clinical factors, were used to estimate risk-adjusted measures of costs, quality, and outcome for each hospital. Association between these measures was evaluated using Pearson correlation coefficient.

RESULTS

In total, 15,415 infants from 104 NICUs were included. Risk-adjusted Baby-MONITOR score, SWMM rate, and costs varied substantially. There was no correlation between risk-adjusted cost and Baby-MONITOR score (r = 0, p = 0.998). Correlation between risk-adjusted cost and SWMM rate was inverse and not significant (r = -0.07, p = 0.48).

CONCLUSIONS

With the metrics used, we found no correlation between cost, quality, and outcomes in the care of VLBW infants.

Association of Parity and Previous Birth Outcome With Brachial Plexus Birth Injury Risk

OBJECTIVE

To evaluate the association of maternal delivery history with a brachial plexus birth injury risk in subsequent deliveries and to estimate the effect of subsequent delivery method on brachial plexus birth injury risk.

METHODS

We conducted a retrospective cohort study of all live-birth deliveries occurring in California-licensed hospitals from 1996 to 2012. The primary outcome was recurrent brachial plexus birth injury in a subsequent pregnancy. The exposure was delivery history (parity, shoulder dystocia in a previous delivery, or previously delivering a neonate with brachial plexus birth injury). Multiple logistic regression was used to model adjusted associations of delivery history with brachial plexus birth injury in a subsequent pregnancy. The adjusted risk and adjusted risk difference for brachial plexus birth injury between vaginal and cesarean deliveries in subsequent pregnancies were determined, stratified by delivery history, and the number of cesarean deliveries needed to prevent one brachial plexus birth injury was determined.

RESULTS

Of 6,286,324 neonates delivered by 4,104,825 individuals, 7,762 (0.12%) were diagnosed with a brachial plexus birth injury. Higher parity was associated with a 5.7% decrease in brachial plexus birth injury risk with each subsequent delivery (adjusted odds ratio [aOR] 0.94, 95% CI 0.92-0.97). Shoulder dystocia or brachial plexus birth injury in a previous delivery was associated with fivefold (0.58% vs 0.11%, aOR 5.39, 95% CI 4.10-7.08) and 17-fold (1.58% vs 0.11%, aOR 17.22, 95% CI 13.31-22.27) increases in brachial plexus birth injury risk, respectively. Among individuals with a history of delivering a neonate with a brachial plexus birth injury, cesarean delivery was associated with a 73.0% decrease in brachial plexus birth injury risk (0.60% vs 2.21%, aOR 0.27, 95% CI 0.13-0.55) compared with an 87.9% decrease in brachial plexus birth injury risk (0.02% vs 0.15%, aOR 0.12, 95% CI 0.10-0.15) in individuals without this history. Among individuals with a history of brachial plexus birth injury, 48.1 cesarean deliveries are needed to prevent one brachial plexus birth injury.

CONCLUSIONS

Parity, previous shoulder dystocia, and previously delivering a neonate with brachial plexus birth injury are associated with future brachial plexus birth injury risk. These factors are identifiable prenatally and can inform discussions with pregnant individuals regarding brachial plexus birth injury risk and planned mode of delivery.

Chronic Hypertension in Pregnancy and Racial-Ethnic Disparities in Complications

OBJECTIVE

To evaluate whether there are individual- and population-level associations between chronic hypertension and pregnancy complications, and to assess differences across seven racial-ethnic groups.

METHODS

This population-based study used linked vital statistics and hospitalization discharge data from all live and stillbirths in California (2008-2018), Michigan (2008-2020), Oregon (2008-2020), Pennsylvania (2008-2014), and South Carolina (2008-2020). We used multivariable log-binomial regression models to estimate risk ratios (RRs) and population attributable risk (PAR) percentages with 95% CIs for associations between chronic hypertension and several obstetric and neonatal outcomes, selected based on prior evidence and pathologic pathways. We adjusted models for demographic factors (race and ethnicity, payment method, educational attainment), age, body mass index, obstetric history, delivery year, and state, and conducted analyses stratified across seven racial-ethnic groups.

RESULTS

The study included 7,955,713 pregnancies, of which 168,972 (2.1%) were complicated by chronic hypertension. Chronic hypertension was associated with several adverse obstetric and neonatal outcomes, with the largest adjusted PAR percentages observed for preeclampsia with severe features or eclampsia (22.4; 95% CI 22.2-22.6), acute renal failure (13.6; 95% CI 12.6-14.6), and pulmonary edema (10.7; 95% CI 8.9-12.6). Estimated RRs overall were similar across racial-ethnic groups, but PAR percentages varied. The adjusted PAR percentages (95% CI) for severe maternal morbidity-a widely used composite of acute severe events-for people who were American Indian or Alaska Native, Asian, Black, Latino, Native Hawaiian or Other Pacific Islander, White, and Multiracial or Other were 5.0 (1.1-8.8), 3.7 (3.0-4.3), 9.0 (8.2-9.8), 3.9 (3.6-4.3), 11.6 (6.4-16.5), 3.2 (2.9-3.5), and 5.5 (4.2-6.9), respectively.

CONCLUSION

Chronic hypertension accounts for a substantial fraction of obstetric and neonatal morbidity and contributes to higher complication rates, particularly for people who are Black or Native Hawaiian or Other Pacific Islander.