A large‑scale study conducted by Dexeus Mujer and recently published in the American Journal of Obstetrics & Gynecology, has shown that pregnancies achieved through frozen embryo transfer in an artificial cycle exhibit significantly lower uterine vascular resistance during the second and third trimester, yet display an incidence of pre‑eclampsia up to four times higher than other modes of conception.

The study analysed 27,495 singleton pregnancies monitored between 2010 and 2024, including natural conceptions, ovulation induction, insemination, fresh embryo transfer IVF and frozen embryo transfer IVF. The results reveal that artificial‑cycle frozen embryo transfers show the lowest uterine pulsatility index values in the second and third trimester, compared with natural pregnancies or natural‑cycle frozen embryo transfers.

Despite this improved uterine perfusion, these pregnancies presented a 5.2% incidence of pre‑eclampsia, markedly higher than that observed in natural pregnancies (1.4%), natural‑cycle frozen embryo transfers (1.1%) or fresh IVF (2.2%). The authors note that this discrepancy highlights a systematic bias in current screening algorithms, which interpret low resistance values as an indicator of low risk.

The Dr Valeria Donno, lead author, emphasises that the findings reinforce the urgent need to revise second‑ and third‑trimester screening algorithms to ensure early identification and appropriate clinical management of high‑risk pregnancies.

The study included the participation of Prof. Kypros Nicolaides, a global pioneer and leading figure in the development of fetal medicine.