The new age of frozen embryo transfer

With this thesis, we aim to provide guidance in the use of frozen embryo transfer (FET) and the ‘freeze-all’ strategy in assisted reproductive techniques. In the beginning, FET was performed based on monitoring the ovulation in the natural cycle of a woman (NC-FET). Later, artificial cycle FET (AC-FET) was developed for women who were anovulatory. Over time, AC-FET became widely used in ovulatory women as well because of its easy alignment with organizational necessities of the clinic. However, the time has come to re-evaluate the use of AC-FET. In this thesis we focus on the safety of mothers and children after NC-FET compared to AC-FET. Based on (our) current research, NC-FET is as effective as AC-FET and safer in terms of obstetric and neonatal outcomes. Therefore, we conclude that that NC-FET is the preferred treatment in women with ovulatory cycles undergoing FET. Based on the results of the national multicentre Antarctica-2 trial, we conclude that home-based monitoring of the ovulation using LH surge urine tests in NC-FET is non-inferior to hospital-controlled monitoring of the ovulation with ultrasounds and hCG-trigger. Home-based monitoring has the major benefit of being more sustainable, saving costs for women and society.
The use of the ‘freeze-all’ strategy should only be adopted if there is a clear clinical indication such as an increased risk of ovarian hyperstimulation syndrome. Applying the use of the ‘freeze-all’ strategy does not lead to higher effectiveness, may increase the risk of adverse obstetric and neonatal outcomes, and increases the time to pregnancy.