A prospective study of semen quality and fecundability among North American couples planning pregnancy.

Background: Few studies have prospectively evaluated semen quality (using the most up-to-date clinically relevant definitions) and fecundability (the per-cycle probability of conception).

Objective: To study semen quality in relation to fecundability.

Materials and methods: We analyzed prospectively collected data from 763 male participants aged ≥21 years from Pregnancy Study Online (PRESTO), a North American preconception cohort study (2015-2024). Eligible participants for the semen testing substudy resided in the contiguous United States, had been attempting conception for ≤6 cycles at cohort entry, and had a female partner aged 21-45 years with regular menses. Participants used an at-home semen testing device to measure semen volume, sperm concentration, and motile sperm concentration. Participants contributed up to two semen tests during the preconception period (1376 total semen samples). We calculated sperm motility, total sperm count, and total motile sperm count. We evaluated results according to 2021 World Health Organization (WHO)-defined thresholds for low semen quality. Female participants reported their pregnancy status on bimonthly follow-up questionnaires for up to 12 cycles or until conception, whichever came first. We used proportional probabilities regression models to estimate fecundability ratios (FRs) and 95% confidence intervals (CIs), adjusting for potential confounders.

Results: After accounting for censoring using life-table methods, 80.7% of couples conceived within 12 cycles. FRs were 1.48 (95% CI, 1.05-2.08) for low semen volume (≤1.5 vs. >1.5 mL), 0.74 (95% CI, 0.56-0.97) for low sperm concentration (≤16 vs. >16 million/mL), 0.98 (95% CI, 0.81-1.19) for low sperm motility (≤42 vs. >42%), 0.58 (95% CI, 0.38-0.88) for low total sperm count (≤39 vs. >39 million), and 0.73 (95% CI, 0.52-1.04) for low total motile sperm count (≤21 vs. >21 million). Associations between low total motile sperm count and fecundability were stronger among couples with <3 cycles of attempt time at cohort entry.

Discussion: In this prospective preconception cohort study of North American couples, most suboptimal semen parameters based on WHO criteria were associated with reduced fecundability, with the exception of low semen volume.

Conclusion: Semen quality at suboptimal levels may adversely affect fecundability.