No Evidence Supports Sex Selection Through Post-Ovulation Intercourse
Having sex after ovulation does not reliably increase the chances of conceiving a male child, and attempting this practice may reduce overall conception rates and potentially increase risks to the pregnancy.
What the Evidence Actually Shows
Timing and Conception Success
The most robust evidence demonstrates that conception occurs almost exclusively during a 6-day fertile window ending on the day of ovulation itself 1, 2. The probability of conception drops to essentially zero after ovulation has already occurred 2. This means that deliberately waiting until after ovulation to have intercourse would dramatically reduce or eliminate the chances of conceiving at all, regardless of desired sex 3, 1.
Sex Ratio and Timing: Conflicting and Unreliable Data
The research on timing of intercourse and baby sex shows contradictory findings:
One older study from 1979 suggested a higher proportion of male babies (65.5%) when intercourse occurred two days after ovulation 4. However, this same study cautioned against attempting this practice due to concerns about potential birth defects from delayed fertilization 4.
The highest quality study directly contradicts this claim: A rigorous 1995 study of 221 women and 625 menstrual cycles found no relationship between the timing of intercourse relative to ovulation and the sex of the baby 2. This study used objective urinary hormone measurements to precisely determine ovulation timing and found that "cycles producing male and female babies had similar patterns of intercourse in relation to ovulation" 2.
Studies claiming sex selection success used fertility awareness methods (tracking cervical mucus) rather than objective ovulation detection, and involved small sample sizes with significant methodological limitations 5, 6.
Why Post-Ovulation Intercourse Is Not Recommended
Conception Window Closes Rapidly
The American Society for Reproductive Medicine recommends that intercourse should occur during the 6-day fertile window, with optimal timing being 1-2 days before ovulation, as sperm need time to capacitate and reach the fallopian tubes 1. Conception probability peaks at 0.33 on the day of ovulation itself and drops to zero after ovulation 2.
Potential Safety Concerns
The 1979 study that suggested higher male ratios with post-ovulation intercourse specifically warned that "couples should be cautioned against attempting to conceive a boy by delaying intercourse until after ovulation, until further research has established whether delayed fertilization causes birth defects" 4. This concern about aging eggs and delayed fertilization remains unresolved.
Evidence-Based Fertility Guidance
Current guidelines from CDC and the Office of Population Affairs recommend that women with regular menstrual cycles should have vaginal intercourse every 1-2 days beginning soon after the menstrual period ends to maximize conception likelihood 3. Deliberately restricting intercourse to only post-ovulation days contradicts this evidence-based recommendation 3, 1.
Bottom Line
For couples trying to conceive, the focus should be on maximizing overall conception chances by having intercourse during the proven fertile window (the 6 days ending on ovulation day), rather than attempting unproven sex selection methods that may reduce conception rates and carry potential risks 3, 1, 2. The most rigorous scientific evidence shows no reliable relationship between intercourse timing and baby sex 2.