This large population-based study demonstrates that the overall adjusted odds for fetal death at term among Somali women is not different compared with the other ethnic groups analyzed. However, the adjusted odds ratios for neonatal death were higher compared with the U.S. born White population up to 40 weeks, after which there was no difference. Compared with U.S. born Black and Hispanic births, there was no difference until after 41 weeks, when the adjusted odds ratios among Somali infants were significantly lower. These relationships did not change after we limited our analysis to women who delivered after SOL.
The pattern for perinatal mortality followed the same pattern observed for neonatal mortality, with rates among Somali newborns higher than for the U.S. born White population, but not significantly different compared with the U.S. born Black and Hispanic population. After 40 weeks the adjusted odds ratios were not significantly different from those of U.S. born White but at 42 weeks, neonatal mortality was lower than rates observed between the two other main minority cohorts. After limiting to women who had SOL, we observed no change in this pattern.
Consistent with previous reports, mean gestational age at delivery after SOL among Somali women was one week later compared with all other ethnicities. The increased post term birth rate reported by the Ohio study shows that the frequency of late term and post term births decreased after comparing Somali women born in Somalia to those born outside of Somalia 1. Although early work suggested that this could be due to acculturation and willingness to follow recommendations when health care provider recommended delivery, this has not been substantiated in subsequent studies 2.
Recent evidence supports elective induction of labor among otherwise healthy women at 39 weeks. This is associated with decreased cesarean delivery rates, and lower perinatal morbidity and mortality 11. Our findings show that among Somali women, although a longer duration of gestation is associated with increased perinatal mortality compared with U.S. born White women it was not increased compared with U.S. born Black and Hispanic women up to 41 weeks. After 41 weeks, these relationships changed with increasing perinatal mortality for all ethnic groups although the increase was much greater for U.S. born Black and Hispanic women.
Prior publications regarding pregnancies in the Somali population have been reported from the states of Washington, Ohio and Minnesota 1,2,21. Work from the states of Washington and Ohio discusses increased rates of late term and post-term births among Somali women, with contradictory data regarding neonatal outcomes and fetal deaths 1,2,22. Adverse outcomes have been documented among Somali women having post term births 1,2. The Washington State study reported increased risk for adverse obstetrical and neonatal outcomes compared with both Black and white newborns 2. Similar neonatal outcome results were not observed from Ohio 1, where pregnancies were less often affected by hypertension yet more often complicated by diabetes, which is consistent with observations from Washington State and prior research done in Minnesota 2,21. The adverse outcomes are increased compared with U.S. born white women but not with U.S. born Black women or African born Black women. An important distinction between the two studies is that the earlier Washington study based gestational age on last menstrual period (LMP) while the Ohio study based gestational age on the best obstetrical estimate1,2. This difference may affect gestational age by as much as 2 to 3 weeks 23.
We did not specifically assess the impact of country of birth or time living in the U.S. among Somali women. Among African and Hispanic immigrant populations in the U.S., it has shown that immigrant women relative to U.S.-born women have a lower rate of preterm birth, lower birth weight and longer pregnancies 7,24, after controlling for the effect of the community, culture, and environment. This effect was attenuated over time 7. The Ohio cohort study also noted that the observed lower rates of prematurity as well as the higher rate of post term birth decreased over time when comparing Somali women born in the U.S. with those born in Somalia 1. Although we did not specifically address preterm birth rates in our study, in Fig. 1 it is evident that late preterm birth rates are lower among Somali women.
Our data does not include all outcomes reported in the previous studies; it does focus the discussion regarding perinatal mortality on neonatal deaths, given the lack of differences in fetal death rates between the ethnicities analyzed. Although most studies have compared Somali neonatal deaths to the U.S. born White population, the evidence is not clear whether the higher neonatal death rates observed, which are similar to that of U.S. born Black and Hispanic women, are dependent on minority or immigrant status, or ethnicity 25–27. The main difference attributable to Somali ethnicity is that neonatal death rates did not increase despite having a greater mean gestational age at delivery. After 41 weeks, it was comparable to that of U.S. born White women and lower than that of the other ethnicities.
Despite having the largest Somali diaspora in the country 1 there is limited information on late term and post term birth rates within this group in Minnesota. Although trends showing the effect of acculturation have reported greater maternal weight gain and preterm births rates, this is limited to early or first generation Somali women 21. Our current analysis has allowed us to evaluate a longer-term effect of acculturation and environment now that there is a generation of Somali women who have been born in the U.S. and are having children of their own.
The data show that despite acculturation, mean gestational age at delivery is delayed by one week within the Somali population compared with the rest of the population. Previous work in Minnesota compared Somali women delivering between 1993 and 1999 with those who delivered between 2000 and 2006. They measured factors hypothesized to reflect acculturation and their relationship to the higher preterm birth rates expected over time among immigrant Somali women. The factors evaluated and thought to reflect acculturation and affect birth outcomes among Somali women such as age at immigration, years lived in the U.S. and English language proficiency did not account for the observed increase in the preterm birth rate. However increased incidence of maternal obesity and gestational diabetes did, suggesting that diet and obesity may play a larger role in the observed increasing rate of preterm birth in this population, while prenatal care utilization prevented preterm birth 21. The association of pregnancy outcome with gestational diabetes (GDM) is consistent with a large meta-analysis of over 120,000 women that evaluated the risk for GDM among migrant women comparted with the non-migrant population. Migrant women had higher rates of GDM than non-immigrant women 28.
Determining whether initiation of birth was spontaneous or by induction of labor, cesarean without labor or membrane rupture is critical in surveillance and etiological research on preterm birth 19. The same holds true for post term birth and risks for adverse perinatal outcome9. Whether factors influencing preterm birth rates can affect post term birth rates remains to be determined. If factors such as diet and the development of GDM can affect the overall duration of pregnancy and timing of SOL, Somali women would provide an excellent reference to evaluate how factors such as dietary changes over time could change perinatal outcomes by shortening duration of pregnancy. It remains to be seen what factors are influencing neonatal mortality in the minority populations included, but it is likely that cultural and socioeconomic factors play a large role especially regarding access to care.
In conclusion, Somali women on average delivery later than the rest of the population. Despite this difference, fetal death rates are not different compared with the rest of the population. Neonatal mortality however is increased compared with the U.S. born White population, but similar to that of other minorities in Minnesota. After 40 weeks, neonatal mortality decreases compared with other minorities and is comparable to that of the U.S. born White population. This information is consistent with previous work demonstrating that minority and immigrant populations have been and continue to be at risk for adverse neonatal outcomes. These findings provide a framework within which to evaluate biological and cultural factors that can affect duration of pregnancy and neonatal outcomes.