Estimation of Day-Specific Probabilities of Conception during Natural Cycle in Women from Babylon

Identifying predictors of the probabilities of conception related to the timing and frequency of intercourse in the menstrual cycle is essential for couples attempting pregnancy, users of natural family planning methods, and clinicians diagnosing for possible causes of infertility. The aim of this study is to estimate the days in which the likelihood of conception happened by using first trimester ultrasound fetal biometry in natural cycles and spontaneous pregnancy, and to explore some factors that may affect them.

This study is retrospective cohort study, with random sampling. It involved 60 pregnant ladies at first trimester; the date of conception was estimated using: i. Crown-rump length biometry (routine ultrasound examinations were performed at a median of 70 days following Last menstrual period or equivalently 10 weeks), ii. Date of last menstrual cycle. Only women with previous infertility and now conceiving naturally with a certain date of Last menstrual period were selected.

The distribution of conception showed a sharp rise from day 8 onwards, reaching its maximum at day 13 and decreasing to zero by day 30 of Last menstrual period. The older and obese women had conceive earlier than younger women but there was insignificants difference between the two groups (P>0.05). According to the type of infertility, the women with secondary infertility had conceived earlier than those with primary infertility. There was a significant difference between the two groups (P<0.05).

Day specific of conception may be affected by factors such as age, BMI, and type of infertility. This may be confirmed by larger sample size in metacentric study.