# Cryopreservation duration does not affect pregnancy or neonatal outcomes in single high-quality blastocyst transfers: a multicenter retrospective study

## TL;DR

Studying thousands of frozen embryo transfers, this paper finds that how long embryos are stored in the freezer does not affect pregnancy or baby outcomes.

## Contribution

This is the first large-scale study showing cryopreservation duration up to 5 years does not harm pregnancy or neonatal outcomes in high-quality blastocyst transfers.

## Key findings

- No significant differences in pregnancy outcomes between short and long cryopreservation durations.
- Neonatal outcomes like birth weight and gestational age were also unaffected by storage duration.
- Results remained consistent after adjusting for confounding factors.

## Abstract

To study the effect of embryo cryopreservation duration on pregnancy and neonatal outcomes in women transferred with high-quality blastocyst during frozen embryo transfer (FET) cycles.

Multicenter Retrospective cohort study.

Three tertiary-care academic medical centers.

This retrospective study included a total of 24,101 women who underwent single high-quality blastocyst transfer during their first FET cycles at three tertiary academic medical centers between January 2016 and June 2023.

Women were categorized into two groups according to the duration of embryo cryopreservation: the short Cryo group consisted of 23,933 women with a storage time of 0–5 years, while the long Cryo group included 168 women with a storage time > 5 years. Women in the long Cryo group were matched to those in the short Cryo group using propensity score matching with a 1:4 ratio.

The pregnancy outcomes and the neonatal outcomes.

After adjusting for potential confounding factors, no significant differences were observed between the two groups in pregnancy outcomes, including biochemical pregnancy (adjust odds ratio [aOR] 1.04, 95% confidence interval [CI], 0.70–1.56; P = 0.831), clinical pregnancy (aOR 1.10, 95% CI, 0.75–1.60; P = 0.638), ectopic pregnancy (aOR 2.15, 95% CI, 0.37–12.56; P = 0.394), miscarriage (aOR 0.95, 95% CI, 0.54–1.69; P = 0.871), and live birth (aOR 1.09, 95% CI, 0.76–1.55; P = 0.646). In addition, no significant differences were observed in neonatal outcomes, including very preterm birth, preterm birth, very low birth weight, low birth weight, high birth weight, birth weight, and gestational age.

Our analysis found no evidence of significant associations between prolonged cryopreservation of high-quality blastocysts and adverse pregnancy or neonatal outcomes.