O-296 Progesterone level is an alternative marker to detect ovulation time in natural cycle frozen-thawed embryo transfers

Abstract Study question Do serum progesterone or LH levels better predict the optimal timing for embryo transfer in true natural cycle frozen-thawed transfers (NC-FET)? Summary answer Performing according to (PL) had similar ongoing pregnancy rates compared levels. What is known already With efficient and safe vitrification techniques, there an increasing trend cycles (FET) over fresh cycles. FET protocols are programmed cycle, NC-FET modified NC-FET. popularity, since it associated with favourable obstetric perinatal outcomes. In NC-FETs, ovulation time critical parameter synchronization of endometrium. literature, surge most commonly used test define time. design, size, duration This prospective cohort study included 183 IVF clinic between March 2022 November 2022. Main outcome measure pregnancy. Participants/materials, setting, methods subfertile women aged 18-40, having regular menstruation a length 24-38 days included. Protocol serial hormone measurements ultrasound monitoring when dominant follicle reached diameter 15-16 mm. Serum level ≥15 IU/l defined as ‘ovulation -1’ Group 1 blastocyst was performed after 6 days. PL > ug/ml day’ 2. results role chance: There were no significant differences baseline characteristics including female age, body mass index, infertility duration, diagnosis number failed two groups. Also, regarding endometrial thickness, embryos transferred, quality PLs at day similar. The overall clinical 59.6% 50.8%. implantation rate 61.7%. 2 49.5%, 50.5% 47.3%, 52.7%, respectively (p 0.05). order detect calculated mathematical modelling (PL(Ov )=a1 eb1 Ov )(Ov:ovulation day; a1,b1:regression coefficients; e:euler number≌2.718) described our previous study. Embryo planned 5,4 3 based on by modelling. Limitations, reasons caution Since this first planning levels, sample size should be increased also change unknown >40 years age. Wider implications findings Progesterone has particular pattern that enables prediction accurately may instead transfer. Trial registration NCT05690360