Early pregnancy complications after frozen-thawed embryo transfer

The authors noted that FET is an important component of ART and that various cyclic regimens are used worldwide due to insufficient evidence to support any particular transfer schedule.

This study analyzed 7,342 pregnancies after FET registered in the Swiss IVF registry between 2014 and 2019.

Women were divided into three groups according to their cycle regimen leading to pregnancy: Low-dose stimulation cycles (n = 984) with or without luteal phase support (SC-FET). and her HRC-FET (n = 5,360).

Mean maternal age was 35.5, 35.6, and 35.3 years in the NC-FET, SC-FET, and HRC-FET groups, respectively.

The rate of previous recurrent miscarriage was low, 0.3% in NC and 0.3% in NC. 0.3% for SC. 0.8% (P. = 0.062).

However, the three FET groups differed significantly in the percentage of patients with chronic anovulatory/polycystic ovary syndrome (PCOS) and endometriosis.

The NC-FET group had the lowest rate of chronic anovulation/PCOS and the highest rate of mild endometriosis at 5.7% and 8.1%, respectively.

In contrast, chronic anovulation/PCOS and severe endometriosis were most prominent in the HRC-FET group: 17.6% and 5.7%, respectively.

The incidence of thyroid disease was 3.4% in NC. 3.2% for SC. 6.2% for HRC (P. < 0.001). However, there were no significant differences in other clinically relevant comorbidities.

The incidence of first trimester bleeding in the first trimester was 3.5% in NC. 4.3% for SC. 8.4% (P. < 0.001).

Similarly, the prevalence of miscarriage at <12 weeks was 19.0% in NC. 19.7% in SC. 29.1% (P. < 0.001).

Multivariate analysis found nearly double the adjusted odds ratio (aOR) for first trimester bleeding comparing HRC-FET with NC-FET. aOR = 1.92. 95% confidence interval (CI): 1.30 to 2.81.

Similarly, the aOR for miscarriage <12 weeks was 1.82. 95% CI: 1.51 to 2.19, respectively.

OR was comparable for HRC-FET and SC-FET.

Also, no difference was found between SC-FET and NC-FET results.

In addition, the incidence of late miscarriage or ectopic pregnancy was similar with the 3-cycle regimen.

Live birth rate per pregnancy was 78.0% in NC. 77.2% of SCs. 68.2% (P. < 0.001).

NC-FET also had the highest singleton delivery rate of 70.5%.

“This study supports adverse early pregnancy outcomes in cycles in which the corpus luteum is suppressed,” the authors wrote.

They also noted that this is the latest large-scale European registry study to assess complications in early pregnancy and live births per pregnancy after FET among three different cycling regimens.

Research results show that “HRC-FET should be avoided and replaced with SC-FET or NC-FET to achieve better pregnancy outcomes.”

However, further studies are needed to elucidate the potential mechanisms underlying the impact of the FET regimen (with or without the corpus luteum) on early pregnancy complications.


Pape J, Levy J, von Wolff M. Complications in early pregnancy after frozen-thawed embryo transfer with different cycling regimens: a retrospective cohort study. Eur J Obstet Gynecol Reprod BiolDecember 2022;279:102-106. doi:10.1016/j.ejogrb.2022.10.015

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