Mackens S, Stubbe A, Santos-Ribeiro S, et al. - Researchers sought to determine the clinical pregnancy rate (CPR) following a frozen embryo transfer (FET) in a natural cycle (NC) after spontaneous ovulation vs after triggered ovulation [natural cycle frozen embryo transfer (NC-FET) vs modified NC-FET]. In a tertiary hospital setting, they performed randomization of 260 patients with a 1:1 allocation into two groups between January 2014 and January 2019. Patients in group A underwent an NC-FET, while in group B, they performed a modified NC-FET with a subcutaneous hCG injection to trigger ovulation. All embryos were vitrified-warmed on Day 3 and transferred on Day 4 of embryonic development. After study arm allocation, 12 patients withdrew consent. Until 10 weeks of gestation when the ongoing pregnancy rate was defined by the observation of foetal cardiac activity on ultrasound scan, the participants were followed. Biochemical pregnancy rate, early pregnancy loss and the number of visits, blood samples and ultrasonographic examinations prior to FET were assessed as other secondary outcomes. Per observed outcomes, there was no significant difference in the CPR between the two FET preparation protocols.