Spontaneous ovulation versus HCG triggering for timing natural-cycle frozen-thawed embryo transfer: a randomized study.

In ovulatory patients, frozen–thawed embryo transfer (FET) is commonly performed during a natural cycle (NC). The objective was to compare serial monitoring until documentation of ovulation with human chorionic gonadotrophin (HCG) triggering, for timing NC-FET. Sixty women with regular menstrual cycles undergoing NC-FET were randomized into two groups: group A (n=30) had FET in a natural cycle after ovulation triggering with HCG; group B (n=30) had FET in a natural cycle after detection of spontaneous ovulation. The main outcome measure was the number of monitoring visits at the clinic per cycle. Secondary outcome measures included implantation rate, clinical pregnancy and live-birth rates. Both groups were similar in terms of demographic characteristics and reproductive history. Clinical and laboratory characteristics of fresh and frozen cycles and pregnancy and delivery rates were comparable for both groups. The number of monitoring visits in group A (3.2±1.4) was significantly lower than in group B (4.7±1.6) (P=0.002). In patients undergoing NC-FET, triggering ovulation by HCG can significantly reduce the number of visits necessary for cycle monitoring without an adverse effect on cycle outcome. Ovulation triggering can increase both patient convenience and cycle cost effectiveness.