Spontaneous LH surges prior to HCG administration in unstimulated-cycle frozen-thawed embryo transfer do not influence pregnancy rates

LH surges are the start of a period of fertility. Missing these surges in natural-cycle frozen-thawed embryo transfer (FET) based on ultrasound alone might lead to incorrect timing of thawing and transferring. This can subsequently lead to diminished pregnancy rates. In this trial we established both the incidence and effect of these LH surges on ongoing pregnancy rates and assessed the use of ultrasound without LH monitoring in planning natural-cycle FET. Over a 2-year period, all patients undergoing natural-cycle FET in our centre were included in this analysis (n = 233). All patients had a regular menstrual cycle. Analyses of the LH concentration took place before ovulation induction with human chorionic gonadotrophin in natural-cycle FET. The main outcome measure was ongoing pregnancy. LH surges occurred in over half of all patients. The overall pregnancy rate was 34.3%. No difference was found in pregnancy rates between patients with and without an LH surge. Based on these results, we concluded that LH surges occurred in over 50% of all patients, but these surges demonstrated no significant effect on pregnancy rates. Regular ultrasound evaluation of the dominant follicle alone seems to be an accurate method to plan natural-cycle FET.