Semen quality and time to pregnancy: the Longitudinal Investigation of Fertility and the Environment Study.
OBJECTIVE: To assess semen parameters and couple fecundity as measured by time to pregnancy (TTP).
DESIGN: Observational prospective cohort with longitudinal measurement of TTP.
SETTING: Sixteen Michigan/Texas counties.
PATIENT(S): A total of 501 couples discontinuing contraception were followed for 1 year while trying to conceive; 473 men (94%) provided one semen sample, and 80% provided two samples.
MAIN OUTCOME MEASURE(S): Using prospectively measured TTP, fecundability odds ratios (FORs) and 95% confidence intervals (CIs) were estimated for 36 individual semen quality parameters accounting for repeated semen samples, time off contraception, abstinence, enrollment site, and couples' ages, body mass indices, and serum cotinine concentrations.
RESULT(S): In adjusted models, semen quality parameters were associated with significantly shorter TTP as measured by FORs >1: percent motility, strict and traditional morphology, sperm head width, elongation factor, and acrosome area. Significantly longer TTPs or FORs <1 were observed for morphologic categories amorphous and round sperm heads and neck/midpiece abnormalities. No semen quality parameters achieved significance when simultaneously modeling all other significant semen parameters and covariates, except for percent coiled tail when adjusting for sperm concentration (FOR 0.99; 95% CI 0.99-1.00). Male age was consistently associated with reduced couple fecundity (FOR 0.96; 95% CI 0.93-0.99), reflecting a longer TTP across all combined models. Female but not male body mass index also conferred a longer TTP (FOR 0.98; 95% CI 0.96-0.99).
CONCLUSION(S): Several semen measures were significantly associated with TTP when modeled individually but not jointly and in the context of relevant couple-based covariates.