Night Shift Work and Fecundability in Late Reproductive-Aged African American Women

Background: We estimated the association between night shift work and fecundability among African American women. Methods: Black Women's Health Study participants ( n  = 560) aged 30-45 years reported their history of night shift work in 2005. Time to pregnancy for all pregnancies resulting in a livebirth was reported in 2011. We estimated the fecundability ratio (FR) and 95% confidence interval (CI) using proportional probabilities regression, accounting for multiple observations of individual women using generalized estimating equations. Results: We observed 4,417 months of pregnancy attempt time resulting in 390 births. After adjustment for covariates, women who reported ever working night shifts had 20% lower fecundability compared with those who never reported night shift work (FR = 0.80, 95% CI: 0.59-1.04). The FR for women reporting night shift work with a frequency of ≥1 time per month and a duration of ≥2 years was 0.65 (95% CI: 0.47-0.94) relative to women reporting no shift work. We observed a decrease in fecundability associated with ever working night shifts (FR = 0.74, 95% CI: 0.56-0.96) among women aged ≥35 years, but not among younger women (FR = 1.33, 95% CI: 0.78-2.28). Conclusion: A history of working night shifts was associated with reduced fecundability among older reproductive-aged African American women attempting pregnancy.