P–760 Cycle outcomes in frozen-thawed single blastocyst transfers in overweight and obese women

Study question Are cycle outcomes different in frozen embryo transfer in obese and overweight women compared to normal weight cases? Summary answer As BMI increases, although implantation rates are similar, miscarriage rates increase and live birth rates decrease, especially in cases whose BMI value is above 30. What is known already Obesity has adverse effects on the reproductive system. Obesity causes ovulatory dysfunction and menstrual cycle disorders, thus reducing fertility. As BMI increases, the implantation, pregnancy and ongoing pregnancy rates decrease and the rate of clinical losses increases. In donor oocyte cycles, the BMI of the recipient has a statistically significant detrimental effect on obstetrics outcomes such as pregnancy rate and live birth rate. However, very few studies evaluate the impact of BMI on frozen-thawed single blastocyst transfer. Study design, size, duration This retrospective study was conducted at Istanbul Memorial Hospital, ART and Reproductive Center between 2011 and 2020. A total of 5642 frozen-thawed single blastocyst transfer cycles were examined. Patients were grouped according to the World Health Organisation BMI classification system: Group I (BMI 25–29.9) (n = 1663); Group II (BMI 30–34.9) (n = 598); Group III (BMI 35–39.9) (n = 150); Group IV (BMI>40) (n = 30); Control Group (BMI 18.5–24.9) (n = 3201). Participants/materials, setting, methods: Patients between 17–42 years old were included. Preimplantation genetic diagnosis (PGD) was performed for patients >37 years old. Exclusion criteria were: repeated pregnancy losses, Mullerian abnormalities, intrauterine adhesions, endometrial thickness <7mm during frozen embryo transfer (FET) cycle. For endometrial preparation, modified natural cycle or artificial cycle were used. Single top/good quality blastocysts were transferred. Main results and the role of chance A total of 5642 FET cycles were analyzed. There was no significant difference in patient characteristics in terms of mean age, endometrial thickness on embryo transfer day and Anti Mullerian Hormone levels between the groups. Cycle outcomes were analysed according to the BMI groups. Mean age of groups were 32.1(17–42), 32(18–42), 32.6(20–42), 32.8(23–42) in groups I to IV respectively and 32(18–42) in the control group. Pregnancy rates were 70.9%(n = 1180) 70.7%(n = 423), 76%(n = 114) and 54.8%(n = 17) in groups I to IV respectively and 72.4% in the control group(n = 2321) (p > 0,05). Clinical pregnancy losses rates were 18.9%(n = 196), 23.9%(n = 86), 23.1%(n = 22) and 23%(n = 3) in groups I to IV respectively and 15.1% in the control group(n = 316) (p < 0,05). The live birth rates were 49.9%(n = 830) 45.1%(n = 270), 47.3%(n = 71) and 33.3%(n = 10) in groups I to IV, respectively and 54.9% (n = 1759) in the control group (p < 0,05). There was no statistically significant difference in implantation rates between the groups but clinical pregnancy losses rates were higher in obese patients (groups II-III-IV) whereas live birth rates were lower compared to group I (overweight) and the control group. Limitations, reasons for caution The limitation of the study is its retrospective nature. Wider implications of the findings: Our study shows that, there is a significantly higher risk of negative cycle outcomes in obese patients. Pre-treatment counselling is therefore needed to increase patient awareness of the risks and to provide advice on weight loss. Trial registration number Not applicable