High oestradiol concentration after ovarian stimulation is associated with lower maternal serum beta-HCG concentration and neonatal birth weight

In this retrospective study, the relationship between maternal serum oestradiol and progesterone levels after fresh embryo transfer or frozen embryo transfer (FET), and serum beta-HCG levels in early pregnancy and neonatal birth weight was examined. Included for analysis were 5643 conceived singletons: 2610 after FET and 3033 after fresh embryo transfer. Outcome measures included maternal serum oestradiol, progesterone, beta-HCG levels during the peri-implantation period, birth weight and small-for-gestational-age (SGA). Results at 4, 5 and 6 weeks' gestation were as follows: serum oestradiol and progesterone levels were significantly higher in women who underwent fresh embryo transfer compared with FET (all P < 0.0001 except progesterone at 6 weeks; P = 0.009); for fresh embryo transfers, serum beta-HCG levels were significantly lower than in women who underwent FET (P < 0.0001); beta-HCG levels were negatively correlated with serum oestradiol; and birth weight was negatively correlated with serum oestradiol. Incidence of SGA in fresh embryo transfer was increased significantly compared with FET (P < 0.001). Higher maternal oestradiol levels after fresh embryo transfer was correlated with lower beta-HCG in early pregnancy, lower birth weight and higher incidence of SGA.