Transferencia de embriones congelados y riesgo de parto prematuro: estudio de la cohorte española

Introduction

Current evidence suggest that perinatal outcomes of children of patients subjected to in vitro fertilisation (IVF) with fresh embryo transfer (ET) are worse compared to frozen embryo transfer (FET). There are doubts if the cause might be related to the technique of vitrification or ovarian stimulation performed in IVF. The aim of this study is to assess the risk of preterm delivery in patients undergoing IVF with fresh ET versus FET.

Material and methods

Retrospective cohort study using data from the National Registry of Assisted Reproduction Techniques Activity - Registry of the Spanish Fertility Society (RNATRA) from 2010 to 2015, including women with a singleton pregnancy following autologous IVF (IVF-AO), or IVF with donation of oocytes (IVF-DO).

Results

A total of 371,308 cycles of IVF were performed, of which 263,306 followed IVF-AO (172,626 fresh ET, and 90,680 FET), and 108,002 underwent IVF-DO (57,944 fresh ET and 50,048 FET). The prevalence of preterm delivery was 12% in IVF-AO group and 18.6% in IVF-DO group. A decreased risk of early preterm delivery was observed after FET only in IVF-AO (OR: 0.87; 95% CI: 0.75-0.99), while an increased risk of late and moderate preterm delivery was found after FET, both in IVF-AO (OR: 1.12; 95% CI: 1.04-1.20) and IVF-DO (OR: 1.17; 95% CI: 1.08-1.26).

Conclusions

Both IVF-AO and IVF-DO have a high prevalence of preterm delivery. Cryopreservation is associated with a lower risk of early preterm delivery compared to fresh ET in patients undergoing IVF-AO; however, an increased risk of late and moderate preterm delivery was observed in both IVF-AO and IVF-DO. These findings should be analysed with caution due to methodological limitations.