Spontaneous ovulation during a natural menstrual cycle represents a simple and efficient method for synchronization between frozen embryos and the endometrium. The objective was to compare serial monitoring until documentation of ovulation, with human chorionic gonadotrophin (HCG) triggering, for timing frozen embryo transfer (FET) in natural cycles (NC). In a retrospective study, 112 women with regular menstrual cycles undergoing 132 NC-FET cycles were divided into two groups: group A (n = 61) patients had FET in an NC after ovulation triggering with HCG; group B (n = 71) patients had FET in an NC after spontaneous ovulation was detected. The main outcome measure was the number of monitoring visits at the clinic. Patients in both groups were similar in terms of demographic characteristics and reproductive history. Clinical and laboratory characteristics of fresh and frozen cycles were also found comparable for both groups, as were pregnancy and delivery rates. The number of monitoring visits in group A (3.46 +/- 1.8) was significantly lower than in group B (4.35 +/- 1.4) (P < 0.0001). 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.