Effect of body mass index on clinical outcomes of the first fresh and frozen-thawed embryo transfer cycle

Abstract

Objective To investigate the effect of body mass index (BMI) on the clinical outcomes of fresh and frozen-thawed embryo transfer in women undergoing in vitro fertilization/intracytoplasmic sperm injection-embryo transfer (IVF/ICSI-ET) cycles. Methods A retrospective analysis was performed at the Center for Reproductive Medicine of the First Affiliated Hospital of Zhengzhou University. The patients who were <35 years and underwent IVF/ICSI treatment were treated with fresh/frozen-thawed embryo transfer for the first time. Patients were divided into low body mass group (BMI<18.5 kg/m2), normal body mass group (18.5-23.9 kg/m2), high body mass group (BMI≥24 kg/m2). The basic conditions of fresh cycles in each group and frozen-thawed cycle pregnancy outcomes were compared. Results 1) The period of infertility, basal endocrine level, gonadotropin (Gn) used dosage and the number of oocytes obtained from the high body mass group were higher than those from the other two groups. Compared with the normal body mass group, the live birth rate (51.93% vs. 48.86%, P=0.007) significantly decreased in the high body mass group, while the abortion rate (14.36% vs. 11.61%, P=0.005) significantly increased. The proportion of macrosomia increased gradually with the increase of BMI in single birth cycle (low body mass group vs. normal body mass group P=0.02, normal body mass group vs. high body mass group P<0.001, low body mass group vs. high body mass group P<0.001). The proportion of low birth weight births in twin delivery cycle decreased with the increase of BMI (P=0.009). 2) During thawing cycles, basal luteinizing hormone (LH), endometrial thickness and live birth rate decreased with the increase of BMI in different BMI groups (P=0.015, P<0.001, P<0.001). The proportion of macrosomia was significantly increased with the increase of BMI in the single birth cycle of frozen-thawed cycles (low body mass group vs. normal body mass group P=0.01, normal body mass group vs. high body mass group P=0.02, low body mass group vs. high body mass group P<0.001). Compared with normal body mass group, the gestational weeks of high body mass group in twin birth cycle were significantly shorter (P<0.001). 3) In each BMI group, the average number of embryos transferred in fresh cycles was lower than that in frozen-thawed cycles (P<0.001), while the embryo implantation rate, clinical pregnancy rate and live birth rate were higher than those in frozen-thawed cycles (P<0.001). In addition, the fresh cycle abortion rate (11.61%) in normal body mass group was lower than that in frozen-thawed cycle (16.10%, P<0.001). Premature birth rate (4.24%), macrosomia (7.23%) and low birth weight (2.55%) in normal birth weight group were lower than those in frozen-thawed cycle (7.52%, 9.47%, 4.38%; P<0.001, P=0.05, P=0.01). The freshly born gestational weeks and the proportion of low birth weight infants in each BMI group were higher than those in frozen-thawed cycle (P<0.001, P=0.007, P<0.001; P<0.001, P=0.0048, P=0.01). The average birth weight in the low body mass group was higher than that in frozen-thawed cycle (P=0.016), while that in the normal body mass group was lower than that in frozen-thawed cycle (P=0.031). Conclusion High BMI in women increases the dosage of Gn used in IVF-ET therapy and may have an adverse effect on oocyte quality and endometrial receptivity. For patients with high BMI, even though the embryo is frozen, clinical pregnancy outcomes cannot be improved. Fresh embryo transfer should be recommended when the patients undergo IVF without other complications. Key words: Body mass index; Embryo transfer; Obesity; Clinical outcome