The modality of endometrial preparation for the transfer of frozen-thawed embryos may influence maternal and fetal adaptation to pregnancy and could thus impact the results of the first trimester combined screening test. We conducted a retrospective cross-sectional study on singleton pregnancies achieved by embryo transfer of a single frozen-thawed blastocyst, comparing two different endometrial preparation protocols: natural cycle (n = 174) and hormone replacement therapy (HRT) (n = 122). The primary outcome was the risk of preeclampsia at the first trimester combined screening test. Secondary endpoints included variable reflecting fetal cardiac function (nuchal translucency and fetal heart rate), maternal adaptation (median arterial blood pressure-MAP and uterine arteries pulsatility index-UtA-PI), and placentation (pregnancy associated plasma protein A and placental growth factor). The risk of early preeclampsia was comparable in the two groups (38% vs. a 28%, p = 0.12). However, women in the natural cycle group showed lower fetal heart rate (159 [155-164] vs. 164 [158-168], p = 0.002) and higher UtA-PI (0.96 [0.74-1.18] vs. 0.72 [0.58-0.90], p < 0.001). The frequency of a screening test at high risk for aneuploidies was similar. The modality of transfer of frozen-thawed embryos is associated with changes in the variables reflecting maternal and fetal cardiovascular function.
Keywords: HRT; first trimester screening test; frozen embryo; in vitro fertilization; natural cycle.