Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby.
Level 3 - non-randomized controlled study
Prospective observational cohort study measuring daily hormonal biomarkers and coital logs.
PubMed 7477165 · doi:10.1056/NEJM199512073332301
What was done
Researchers tracked 221 healthy women planning to conceive who ceased contraception, recorded daily sexual intercourse, and provided daily urine samples. Daily urinary estrogen and progesterone metabolites were analyzed to estimate the day of ovulation across 625 menstrual cycles. Early pregnancy was detected by urinary human chorionic gonadotropin (hCG).
What was found
A total of 192 pregnancies occurred across 625 evaluated cycles, with 129 ending in live births. Conception occurred exclusively when intercourse took place within a six-day window ending on the day of ovulation. The probability of conception rose from 0.10 when intercourse occurred five days before ovulation to 0.33 on the day of ovulation. Only 6% of pregnancies could be attributed to sperm aged three or more days, and sperm age showed no link to pregnancy loss. Timing of intercourse relative to ovulation did not differ between cycles resulting in male versus female live births.
Why it matters
This study defines the human fertile window as a six-day interval ending on ovulation day and refutes the common belief that intercourse timing influences the sex of the infant.
Limits
The study evaluated only healthy women trying to conceive, which may limit generalizability to individuals with subfertility or irregular cycles. Ovulation timing was estimated based on urinary hormone metabolite patterns rather than direct visualization via ultrasound, introducing potential measurement error in pinpointing the exact day of ovulation.
Cited by
- supports Intercourse during the two days before and the day of ovulation carries a 20% to 30% probability of conception, whereas intercourse the day after ovulation has a 0% probability.
- supports Sperm can survive in the human female reproductive tract for up to 5 days, with most remaining viable for around 2 days.