Increased Likelihood of Pregnancy from Sex on the Two Days Before Ovulation [5B]

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Home ovulation tests are a convenient method to maximize chances of becoming pregnant naturally. This study examined intercourse patterns in women using tests and likelihood of pregnancy in relation to timing.


Women seeking to conceive used Clearblue Advanced digital ovulation tests to time intercourse, kept an intercourse diary and collected daily urine samples for 1 cycle. The home ovulation tests detect estrogen rise to identify the onset of the fertile period (approximately 4 days prior to ovulation) and Lutenising hormone (LH) surge (24h prior to ovulation). LH was also measured using AutoDELFIA to assign ovulation day. From the wider population of 1925 volunteers with sufficient data, comparative analysis was conducted on all viable pregnancies (n=288), and a random selection of ovular cycles from not pregnant volunteers (n=677).


One cycle conception rate was 15%. Women were able to effectively target intercourse to their fertile period using home tests, with >60% having sex on day of LH surge compared to <30% in the luteal phase. More women who became pregnant had sex on the day -1 (p=<0.0001) and -2 (p=0.001) prior to ovulation; with an increased likelihood of pregnancy of 18.5% for day-1 and 23.6% for day -2. The day after the LH surge saw a marked decrease in pregnancy rates.


Women using home tests do target intercourse effectively to the fertile window, and there is an increased likelihood of pregnancy with successful timing. Sex on the day preceding the LH surge, which identifiable only by home tests that measure estrogen, significantly increases likelihood of pregnancy.

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