Infant outcome of 957 singletons born after frozen embryo replacement: The Danish National Cohort Study 1995-2006

Objective: To examine infant outcome of singletons born after cryopreservation of embryos (Cryo). Design: National population-based controlled follow-up study. Setting: Denmark, 1995-2007. Patient(s): The study population was 957 Cryo singletons (Cryo-IVF, n = 660; Cryo-ICSI, n = 244; Cryo-IVF/ICSI, n = 53). The first control group was all singletons born after fresh IVF or intracytoplasmic sperm injection (ICSI) during the same period (IVF, n = 6904; ICSI, n = 3425). The second control group comprised a random sample of non-assisted reproductive technology (ART) singletons (n = 4800). Intervention(s): All observations were obtained from national registers. Main Outcome Measure(s): Low birth weight (LBW; <2500 g), preterm birth (PTB; <37 weeks), congenital malformations, mortality, and morbidity. Result(s): Birth weight was higher in Cryo (mean = 3578 g, SD = 625) versus fresh (mean = 3373 g, SD 648) and in Cryo versus non-ART (mean = 3537 g, SD 572), and this was also the case for first birth only. Lower adjusted risk of LBW (odds ratio [OR] = 0.63; 95% confidence interval [CI], 0.45-0.87) and PTB (OR = 0.70; 95% CI, 0.53-0.92) was observed in Cryo versus fresh. Similar LBW and PTB rates were observed when comparing Cryo with non-ART, but the perinatal mortality rate was doubled in Cryo (1.6%) compared with non-ART (0.8%) singletons, and the adjusted risks of very preterm birth (<34 weeks) and neonatal admittance were also significantly increased. No significant differences in the prevalence rates of birth defects, neurological sequelae, malignancies, and imprinting-related diseases were observed between the Cryo and the two control groups. However higher malformation and cerebral palsy rates were observed in the total Fresh vs. non-ART group. Conclusion(s): Cryo singletons have better neonatal outcome than offspring after fresh ET but poorer compared with non-ART singletons. (Fertil Steril (R) 2010;94:1320-7. (C) 2010 by American Society for Reproductive Medicine.)