Effect of follicle size on pregnancy outcomes in patients undergoing first letrozole-intrauterine insemination.

Abstract

Letrozole has been proven to be an effective method for inducing ovulation. However, littleattentionhasbeenpaidto whether the lead follicle size will affect the success rate of intrauterine insemination (IUI) with ovulation induction with alone letrozole. Therefore, we hope to investigate the effect of dominant follicle size on pregnancy outcomes on human chorionic gonadotropin (hCG) day of the first letrozole-IUI. A retrospective cohort study design was employed. We included patients with anovulation or unexplained infertility undergoing first IUI treatment with letrozole for ovarian stimulation. According to the dominantfolliclesize measured on the day of hCG trigger, patients were divided into six groups (≤ 18mm, 18.1-19.0mm, 19.1-20.0mm, 20.1-21.0mm, 21.1-22.0mm, > 22mm). Logistic models were used for estimating the odds ratios (ORs) with their 95% confidence interval (CIs) for achieving aclinicalpregnancyor alivebirth. A restricted cubic spline was drawn to explore the nonlinear relationship between follicle size and IUI outcomes. A total of 763 patients underwent first letrozole-IUI cycles in our study. Fisherexact test showed significant differences among the six follicle-size groups in the rates of pregnancy, clinical pregnancy and live birth (P < 0.05 in each group). After adjusting the potential confounding factors, compared with the follicles ≤ 18mm in diameter group, 19.1-20.0mm, 20.1-21.0mm groups were 2.3 or 2.56 times more likely to get live birth [adjusted OR = 2.34, 95%CI (1.25-4.39); adjusted OR = 2.56, 95% CI (1.30-5.06)]. A restricted cubic spline showed an invertedU-shaped relationship between the size of dominant follicles and pregnancy rate, clinical pregnancy rate, and live birth rate, and the optimal follicle size range on the day of hCG trigger was 19.1-21.0mm. When the E2 level on the day of hCG trigger was low than 200pg/mL, the clinical pregnancy rates of 19.1-20.0mm, 20.1-21.0mm groups were still the highest. The optimal dominant follicle size was between 19.1 and 21.0mm in hCG-triggered letrozole-IUI cycles. Either too large or too small follicles may lead to a decrease in pregnancy rate. Using follicle size as a predicator of pregnancy outcomes is more meaningful when estrogen on the day of hCG trigger is less than 200pg/ml.