Racial variation in the number of spontaneous abortions before a first successful pregnancy, and effects on subsequent pregnancies

OBJECTIVE: To assess the relationship between race and spontaneous abortion, whether the relationship varies by risk factors, and the effect of spontaneous abortions on subsequent pregnancies. METHODS: A retrospective study was undertaken using data collected in London, UK, between 1988 and 2000. Logistic regression evaluated histories of spontaneous abortion and associations with small-for-gestational-age and preterm births in black African, black Caribbean, and South Asian women relative to white European women. Interactions with risk factors were assessed. RESULTS: Overall, 196 040 women were included. Compared with white Europeans, the odds of a previous spontaneous abortion were increased in black African (adjusted odds ratio [aOR] 1.20; 95% confidence interval [CI] 1.12–1.29) and black Caribbean women (aOR 1.31; 95% CI 1.21–1.41). The strength of the association with black African race increased with age (P = 0.002), and the association with South Asian race increased with age and body mass index (P < 0.001 for both). Spontaneous abortion was associated with preterm birth in all races, but was strongest in black African women (aOR 1.47; 95% CI 1.29–1.67). CONCLUSION: The greater incidence of spontaneous abortion in black African and black Caribbean women should prompt further study of risk factors in relation to race. The interaction with age in black African and South Asian women could be important for counseling in relation to timing of pregnancy.