Obstetric and neonatal outcomes after transfer of vitrified early cleavage embryos

Does vitrification and warming of Day 3 embryos have an impact on neonatal outcome when compared with Day 3 embryos that are slow cooled and thawed, or with embryos from a fresh cycle?

The median birthweight was higher in the vitrified group versus the slow cooled or fresh embryo transfer, and the rate of low birthweight in twin babies was lower in the vitrified group.

Vitrification has been successfully used for cryopreserving human oocytes and blastocyst-stage embryos. Most published studies looking at the neonatal outcomes after transfer of vitrified embryos refer to blastocyst-stage embryos. Information on children born after transfer of Day 3 vitrified embryos is relatively rare.

A retrospective, single-centre study of children born after Day 3 embryo transfer from fresh, slow frozen or vitrified embryos during the period January 2006 to May 2011 was conducted. Each patient contributed only one cycle per group. Children born were followed-up at 7-30 days after delivery. Outcome measures include obstetric and neonatal outcomes, which were evaluated by medical records and questionnaires sent to parents.

Patients underwent transfer of vitrified Day 3 embryos (n = 2617 transfers, Cryotop method), slow frozen Day 3 embryos (n = 4681) and fresh Day 3 embryos (n = 9194). All cycles were performed at the Shanghai Ji Ai Genetics & IVF Institute.

Frequencies of hypertensive disorder, gestational diabetes, placenta previa and abruptio placenta were similar in all groups. Five hundred and forty five, 986 and 1914 singleton babies were born from vitrified, slow freezing and fresh transfers, and the median gestational ages were 38.7, 38.7 and 38.7 weeks, respectively. Preterm birth (32-37 weeks) occurred in 7.5, 9.2 and 7.8% of the vitrified, slow freeze and fresh groups, respectively. The median birthweight from vitrified embryos (3455.3 g) was higher than that from slow freezing (3352.3 g) and fresh (3355.8 g) transfers (P < 0.0001 for both). The rate of perinatal mortality was 0.4% for all transfer groups. Three hundred and eighty two, 734 and 1322 twin babies were born from vitrified, slow freezing and fresh transfers, respectively. There were no differences among groups in mean gestational age and in the rate of preterm birth. The median birthweight for babies born from vitrified embryos (2587.4 g) was higher than that from the slow freezing (2538.8 g) or fresh (2494.4 g) transfer groups (vitrified versus fresh: P = 0.0015; vitrified versus slow freeze: P = 0.049). The rate of low birthweight (1500-2500 g) from vitrified (30.4%) was lower than that from fresh (36.2%) transfer (P = 0.034).

The main limitation of this study is that the obstetric and neonatal data were obtained by questionnaires sent to the parents without checking medical records. This is, especially, problematic for reporting on congenital malformations, so birth defects were excluded from the data.

Transfer of vitrified and warmed Day 3 embryos does not seem to have an adverse effect on neonatal outcome. Children born following the transfer of vitrified embryos seem to have a higher birthweight when compared with those of fresh or slow frozen embryos.

This study received no outside funding and none of the authors has any conflict of interest.