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.

Key Words: Congenital malformation, cryopreserved embryos, follow-up, frozen embryo replacement, neonatal outcome