RESUMO
BACKGROUND: The higher prevalence of preterm birth (PTB) and low birthweight (LBW) following infertility treatment may relate to the treatment itself or indicate that subfertility predisposes to a higher risk. Our aim was to examine whether basal FSH levels are related to the risk for PTB and LBW among pregnancies resulting from IVF. METHODS: We studied a retrospective cohort in the 2008 National Society for Assisted Reproductive Technology Database, including all women who underwent a fresh non-donor IVF cycle resulting in a singleton live birth having a recorded basal serum FSH value (n = 14 262). The FSH value used was either the maximum basal or clomiphene-stimulated serum level. Log binomial models were created to assess the associations between FSH and PTB (<37 weeks), and between FSH and LBW (<2500 g), adjusting for maternal age, ethnicity, gravidity/parity, history of PTB, smoking, BMI and infant gender. RESULTS: Data for 14 086 patients were analyzed. FSH levels were inversely related to the risk of PTB and LBW. Women in the highest quartile of FSH levels (≥ 9 mIU/ml) had the longest adjusted mean gestational age (271.2 days), the lowest adjusted relative risk (RR) of PTB [0.87, 95% confidence interval (CI): 0.76-1.01], the highest adjusted mean birthweight (3249 g) and the lowest adjusted RR of LBW (0.89, 95% CI: 0.73-1.04). CONCLUSIONS: The inverse relationship between maximal basal FSH levels and the risk for PTB and LBW in singleton IVF gestations suggests that diminished ovarian reserve is not the primary mediator of the increased prevalence of PTB and LBW in IVF pregnancies.