Racialized economic segregation in relation to fecundability in a preconception cohort study

Racialized economic segregation is a known determinant of health disparities that has been associated with adverse pregnancy outcomes. However, no study has investigated its association with fecundability, the per-cycle probability of conception. We analyzed data from 10,438 U.S. participants enrolled in Pregnancy Study Online (2013-2022), an internet-based preconception cohort study. Eligible participants were aged 21-45 years, assigned female at birth, and trying to conceive without fertility treatment use. Using baseline residential addresses, we calculated segregation based on the Index of Concentration at the Extremes (ICE) from the American Community Survey 5-year estimates. ICE ranges from -1 ("disadvantaged") to 1 ("privileged"). We operationalized ICE metrics at the census tract level: economic segregation (ICE_income: ≥ $100 k vs. < $25 k), racial segregation (ICE_white/black: non-Hispanic White vs. non-Hispanic Black), and racialized economic segregation (ICE_{income + white/black}: non-Hispanic White ≥ $100 k vs. non-Hispanic Black < $25 k). We used proportional probabilities regression models to estimate fecundability ratios (FRs) and 95% confidence intervals (CIs), adjusting for precision variables. We observed a monotonic inverse association for increasing quintiles of ICE_income and ICE_{income + white/black} with fecundability, but less evidence of associations with ICE_white/black. For instance, relative to ICE_{income + white/black} quintile 5 ("most privileged"), FRs for quintiles 4, 3, 2, and 1 ("most disadvantaged") were 0.92 (95% CI = 0.86-0.99), 0.84 (95% CI = 0.78-0.90), 0.84 (95% CI = 0.78-0.90), and 0.79 (95% CI = 0.73-0.86), respectively. Living in the most disadvantaged neighborhoods with respect to racialized economic segregation was associated with a moderate decrease in fecundability.