Risk of low birth weight infants in women conceived through in vitro fertilization and fresh embryo transfer

Abstract

Objective To analyze the risk factors of low birth weight (LBW) in infants who were conceived through fresh embryo transfer after in vitro fertilization. Methods We retrospectively reviewed the medical records of 4 930 live babies born after in vitro fertilization/intra-cytoplasmic sperm injection- embryo transfer (IVF/ICSI-ET) at Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University between January 2011 to December 2016. They were 3 474 singletons and 1 456 pairs of dizygotic twins. According to their birth weight, all singletons were divided into two groups: the LBW singleton group (<2 500 g, n=252) and the control singleton group (≥2 500 g, n=3 222). Two dizygotic twin groups, the LBW dizygotic twin group (<2 500 g, n=1 014) and the control dizygotic twin group (≥2 500 g, n=442), were set up as well. Clinical characteristics of the infants in different groups and risk factors of LBW were analyzed. Independent samples t-test, Mann-Whitney U test, Chi-square test, and logistic regression were used for statistical analysis. Results (1) The rates of LBW were 7.25% (252/3 474) in singletons and 69.64% (1 014/1 456) in dizygotic twins. (2) In singleton pregnancies, the maternal body mass index (BMI) of the LBW group was lower than that of the control group [(20.9±2.8) vs (21.3±2.7) kg/m2, t=2.162, P=0.031], while the rates of preterm delivery and blastocyst transfer were higher [61.7% (153/252) vs 5.7% (182/3 222), 8.7% (22/252) vs 5.1% (163/3 222), χ2=814.232 and 6.234, respectively, all P 10 970 pmol/L) and different gender of twins were independent risk factors for LBW in dizygotic twin pregnancies (adjusted OR=4.51, 1.35 and 1.45, 95%CI: 3.50-5.82, 1.06-1.74 and 1.09-1.93, all P<0.05). Conclusions High maternal serum E2 level after controlled ovarian stimulation (COS) in fresh embryo transfer cycle may be one of the risk factors for LBW in twin pregnancies. Key words: Infant, low birth weight; Fertilization in vitro; Embryo transfer; Estradiol; Ovulation induction; Risk factors