Women whose previous delivery had been by cesarean had a rate of stillbirth in their subsequent pregnancy similar to that of women who had had a vaginal delivery, according to a longitudinal study of Missouri births.1 However, black women had a higher rate of stillbirth than white women, and blacks who had had a cesarean were more likely to have a stillbirth than were blacks who had delivered vaginally. A second study by the same team of researchers using the same data found that the rate of stillbirth in the second pregnancy was higher for those who had had a stillbirth than for those who had not.2 Blacks experienced a higher rate of recurrence of stillbirth than whites.
Stillbirth Following Cesarean Delivery
The rate of cesarean deliveries in the United States has been increasing since 1996, and one in three births among black women are by cesarean, which is the highest rate for any racial group. Blacks also have a greater risk of having stillbirths, and the rising use of cesarean delivery may be disproportionately affecting this group.
The Missouri cohort data set for the period 1978–1997 identifies and links newborns to their biological mothers. To assess the association between cesarean delivery and stillbirth in subsequent pregnancy, the researchers examined the records of women who had had two consecutive singleton births at 20 or more weeks of gestation; infants with congenital abnormalities were excluded. A stillbirth was defined as intrauterine fetal death at a gestational age of 20 or more weeks.
Because this study focused on the outcome of the second pregnancy, data on maternal characteristics at the later pregnancy were used; these included age, educational level, race, marital status, cigarette smoking, adequacy of prenatal care (using an index based on the trimester in which care began, number of visits and gestational age at birth) and body mass index. The occurrence of obstetric complications in the second pregnancy was also examined. Chi-square and t tests analyzed differences in these characteristics between subgroups. Multivariable logistic regression analysis was used to assess associations between cesarean delivery and subsequent stillbirth; regression models controlled for the foregoing maternal characteristics, as well as for parity, interpregnancy interval and year of birth.
Of the 396,441 women in the sample, 82% delivered vaginally and 18% by cesarean in their first pregnancy. Compared with the proportion among women who had had a vaginal delivery, higher proportions of those with a previous cesarean had 12 or more years of education (86% vs. 81%) and were 35 or older (10% vs. 7%), white (88% vs. 84%), married (84% vs. 80%) and overweight or obese (31% vs. 21%). A higher proportion of these women had received adequate prenatal care (51% vs. 40%), while a lower proportion had smoked during the second pregnancy (23% vs. 26%). Greater proportions of women who had had a cesarean experienced medical complications in their second pregnancies, including anemia, cardiac disease, diabetes, chronic hypertension, preeclampsia, eclampsia and placental disorders. Overall, 18% of women who had undergone this procedure had any medical complication, whereas 14% of those who had not had it suffered a complication. The cesarean group also had a slightly higher rate of preterm births, but there was no difference between the groups in the proportion of infants who were small for gestational age.
In all, 1,612 pregnancies ended in stillbirths; no difference was found in the stillbirth rate between women who had had vaginal and those who had had cesarean delivery (4.4 per 1,000 for each group). However, blacks had a significantly higher rate of stillbirth than whites (7.2 vs. 3.6 per 1,000). Furthermore, while the rate of stillbirth did not differ between whites who had had a vaginal delivery and those who had undergone a cesarean, blacks who had had a cesarean delivery experienced a higher rate of stillbirth than those who had had a vaginal delivery (9.3 vs. 6.8 per 1,000). The adjusted analyses confirmed that black women with a previous cesarean had a higher risk of stillbirth than blacks who had delivered vaginally (odds ratio, 1.4). Further analysis by gestational age found a higher risk among blacks only for 35 or more weeks (1.4); the same risk for stillbirth was found when both gestational age and occurrence of medical complications were controlled for.
A major strength of the study, the researchers note, is the robust data set, which is considered a national standard. Limitations include scarce data on placental abnormalities and causes of stillbirth, and the aggregation of different infant cohorts. The researchers believe that the upsurge in cesarean deliveries over the last decade may be caused by changes in physician behavior and institutional practices, and that these changes may be a factor in black women's increased rates of both cesareans and stillbirth. They suggest that future research should examine whether there is a causal relationship between undergoing a cesarean and having a subsequent stillbirth.
Race and Stillbirth Recurrence
In the second study, the researchers examined whether race was a determinant of stillbirth recurrence. They looked at women who had had consecutive singleton births in which the fetus was between 20 and 44 weeks of gestational age. Analyses were similar to those conducted in the other study.
The sample included 404,180 women, of whom 99.5% had had a live birth and 0.5% had had a stillbirth in the first pregnancy. The two groups differed significantly in all characteristics but maternal age and educational level. Compared with the proportions among women who had not had a previous stillbirth, higher proportions of those who had had one were black (20% vs. 14%), unmarried (22% vs. 19%) and overweight or obese (28% vs. 23%). Higher proportions had smoked during pregnancy (28% vs. 26%) and had received adequate prenatal care (58% vs. 42%). These women also had higher rates of nearly all medical complications in their second pregnancies (anemia being the exception); 30% experienced at least one complication, compared with 20% of women who had not had a stillbirth.
Among the women in the sample, 1,929 had a stillbirth in the second pregnancy. The rate of stillbirth was significantly different between women who had had an earlier stillbirth and those who had not (22.7 vs. 4.7 per 1,000). Rates were dramatically different depending on race: Black women who had experienced earlier stillbirth and those who had not had rates of 35.9 and 7.6 per 1,000, respectively, while white women had rates of 19.1 and 4.2 per 1,000, respectively. The overall likelihood of stillbirth was significantly elevated for women with a previous stillbirth (odds ratio, 4.7). Among these women, the risk of stillbirth recurrence was higher for blacks than for whites (2.6) after potential confounders were controlled for.
According to the researchers, strengths of this study are that it is population-based and that, unlike previous studies, it accounts for the effect of maternal body mass index, which is a critical cause of adverse pregnancy outcomes. However, the research also has a number of limitations: It did not assess the influence of maternal and fetal medical conditions, and there were few cases of stillbirths available for the racial analysis.
The researchers assert that there is a critical need to explore the risk profiles of women and to develop public health programs to ameliorate the racial disparity in the rate of stillbirth recurrence. They suggest that these programs include counseling and possibly changes in clinical practice to better serve the differing needs of patients. While this study highlights the need for a more comprehensive research agenda in this area, the researchers believe that their findings "will contribute to the enhancement of our current understanding of stillbirth recurrence, an area that has been poorly researched."—J. Thomas
1. Salihu HM et al., Risk of stillbirth following a cesarean delivery: black-white disparity, Obstetrics & Gynecology, 2006, 107(2, pt. 1):383–390.
2. Sharma PP et al., Is race a determinant of stillbirth recurrence? Obstetrics & Gynecology, 2006, 107(2, pt. 1):391–397.