The ranges of the periods between changes in LH concentration, i.e., either the first increase or the peak, and ovulation in individual women’s data extend over 24 h, which suggests that if FET is scheduled solely based on LH concentrations, in some women, a blastocyst could be transferred on a different day than the targeted 5th day after ovulation, i.e., start of secretory transformation, leading to lower implantation or higher miscarriage rates [23]. The gene discussed is PLOD1; the disease is spontaneous abortion.