This study compared the pregnancy and neonatal outcomes between fresh embryo transfer and frozen-thawed embryo transfer (FET). These patients were split into two groups: the fresh embryo transfer group and the FET group. The general conditions, pregnancy outcomes, and neonatal outcomes between these groups were compared. The influencing factors of fetal macrosomia occurrence were explored as well. Compared with the fresh embryo transfer group, the FET group had a significantly higher mean age (32.59 ± 4.77 vs. 31.90 ± 4.71, p < 0.05) and lower multiple pregnancy rate (21.2% vs. 26.9%, p < 0.05). There was no significant difference in the incidence of congenital anomalies of neonates between the two groups (1.32% vs. 0.37%, p > 0.05). In the FET group, compared with the fresh embryo transfer group, the mean birth weight of singleton live births, the cesarean section rate, and the incidence of fetal macrosomia were significantly increased, while the incidence of low birth weight was significantly decreased. The logistic analysis showed that the occurrence of fetal macrosomia was primarily associated with the embryo transfer protocol (odds ratio [OR] = 2.769, 95% confidence interval [CI]: 1.246-6.154, p < 0.05), endometrial thickness (OR = 1.144, 95% CI: 1.043-1.256, p < 0.05), and gestational age (OR = 1.710, 95% CI: 1.338-2.184, p < 0.05). Macrosomia (OR = 2.938, 95% CI: 1.436-6.010, p = 0.003) and multiple pregnancy (OR = 3.574, 95% CI: 2.616-4.882, p < 0.001) significantly increased the cesarean section rate. The risk of fetal macrosomia and congenital anomalies in the offspring of the fresh embryo transfer group was lower than that in the offspring of the FET group, we preferred to fresh embryo transfer for patients with assisted reproductive technologies. FET should be used as supplementary therapeutic strategy with strengthened pregnancy management and screening to reduce the occurrence of birth defects in newborns.
Keywords: congenital anomalies; fetal macrosomia; fresh embryo transfer; frozen-thawed embryo transfer; low birth weight.