Estimation of follicular growth-widely used, seldom studied.

We assessed whether estimation of follicular growth, rather than actual measurement of follicular size on the day of hCG trigger, affected pregnancy rates in intrauterine insemination (IUI) cycles. Patient and cycle characteristics were extracted from an existing database. Comparisons were made between the pregnant (defined as a positive beta hCG) and non-pregnant groups for the following variables: patient's age, number of previous IUI cycles, type of ovarian stimulation, endometrial thickness, number of follicles measuring 14 mm and above, pre and post wash sperm parameters, cycle day when IUI was done and number of days between last ultrasound scan and ovulation trigger. A total of 7302 cycles were included in the final analysis. In 4055 cycles (55.5%) the hCG trigger was on the day of the last ultrasound, in 2285 cycles (31.3%) the hCG trigger was 1 day after the last ultrasound, in 850 (11.6%) it was 2 days after the last ultrasound and in 112 (1.5%) it was 3 or more days after the last ultrasound. Sperm parameters, younger maternal age, and the number of follicles above 14 mm were all associated with pregnancy. No association was found between positive pregnancy test rates and the time from last ultrasound to hCG trigger. Planning IUI based on the estimation of follicular growth 1-4 days before trigger, does not affect pregnancy rates.