Vitrified-warmed embryo transfer is associated with mean higher singleton birth weight compared to fresh embryo transfer

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Abstract

Objective

To test for differences in birth weight between singletons born after IVF with fresh embryo transfer vs. vitrified-warmed 2PN embryo transfer (vitrification protocol).

Design

Retrospective analysis of 464 singleton live births after IVF or ICSI during a 12 year period.

Setting

University hospital.

Interventions

Fresh embryo transfer, vitrified-warmed 2PN embryo transfer (vitrification protocol).

Main outcome measures

Birth weight standardized as a z-score, adjusting for gestational week at delivery and fetal sex. As a reference, birth weight means from regular deliveries from the same hospital were used. Multivariate regression analysis was used to investigate the relationship between the dependent variable z-score (fetal birth weight) and the independent predictor variables maternal age, weight, height, body mass index, RDS prophylaxis, transfer protocol, number of embryos transferred, indication for IVF treatment and sperm quality.

Results

The mean z-score was significantly lower after fresh transfer (−0.11 ± 92) as compared to vitrification transfer (0.72 ± 83) (p < 0.001). Multivariate regression analysis indicated that only maternal height and maternal body mass index, but not type of cryopreservation protocol, was a significant predictor of birth weight.

Conclusions

In this analysis focusing on 2PN oocytes, vitrified-warmed embryo transfer is associated with mean higher birth weight compared to fresh embryo transfer. Maternal height and body mass index are significant confounders of fetal birth weight and need to be taken into account when studying birth weight differences between ART protocols.

Introduction

Cryopreservation of embryos or 2 PN oocytes and later transfer have become important tools in modern assisted reproductive techniques. During the last years, US and European registries report increasing numbers of babies delivered after cryopreservation of embryos [1], [2], [3]. Therefore, the evaluation of the safety of cryopreservation in terms of child health is utterly important.

A variety of freezing and thawing protocols have been reported in literature. Additionally, the type of cryopreserved tissue differs between countries as cryopreservation of embryos is not allowed everywhere. These facts highlight the difficulties in judging safety aspects of cryopreservation in literature as protocols differ from each other.

Several systematic reviews and cohort studies have indicated similar or even better neonatal outcomes for singletons born after cryopreservation compared to singletons born after fresh transfer [4], [5], [6], [7]. However, also higher rates of large for gestational age (LGA) and/or macrosomic infants were observed after cryo-transfer compared to singletons after spontaneous or fresh transfer. Of note, most studies have analyzed data on embryo cryopreservation and not 2PN oocyte cryopreservation [8], [9].

The aim of the present study therefore was to explore differences in birth weight of singleton deliveries after fresh embryo transfer and vitrified-warmed 2PN embryo transfer (vitrification protocol), respectively.

Section snippets

Materials and methods

The present study is a retrospective exploratory analysis based on data logged in the local IVF and labour ward software databases (Recdate Advance©; View Point® 6.0, GE Healthcare). The data were retrieved in January 2014. Approval from the Institutional Review Board was obtained before data collection, and the protocol was prospectively registered (NCT 01088425). The study included data on singleton deliveries after fresh embryo transfer in IVF or ICSI cycles and embryo transfer after

Results

In total, 464 singleton live births after IVF/ICSI met the inclusion criteria and were analyzed: 276 live births after fresh transfer (151 male/125 female) and 188 live births after vitrification transfer (106 male/82 female). Mean maternal age was 33.4 years with a SD of 4.1 years. Table 1 depicts an overview of baseline, treatment and outcome parameters in the two groups.

Discussion

Herein we show that vitrified-warmed 2PN embryo transfer is associated with mean higher birth weight for singletons compared to fresh embryo transfer. No association was found for the indication for ART treatment (male, female, idiopathic, both) and the sperm quality. Of note, in this cohort of singletons, the previously demonstrated association between number of embryos transferred and lower birth weight [13], [14], [15], [16] was also not confirmed. The difference in birth weight observed

References (21)

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