Pregnancies achieved through assisted reproductive technology (ART) are associated with more obstetric complications than natural pregnancies.

In pregnancies achieved through in vitro fertilization, different obstetric outcomes are observed depending on the type of embryo transfer performed and the type of endometrial preparation. Studies comparing obstetric complications according to the type of transfer performed (fresh or frozen embryo transfer) suggest an increased risk of preeclampsia, fetal macrosomia, and postpartum hemorrhage in pregnancies achieved through frozen embryo transfer.

Depending on the endometrial preparation methods used prior to frozen embryo transfer, different obstetric risks are observed. Comparisons mainly focus on stimulated cycles versus natural cycles and spontaneous pregnancies. Pregnancies achieved through frozen embryo transfer in a stimulated cycle are thought to be at greater risk of preeclampsia, fetal macrosomia, and postpartum hemorrhage than natural cycles and spontaneous pregnancies. One of the first markers of this vascular adaptation is the cranio-caudal length (CCL).

Indeed, the cranio-caudal length of embryos in the first trimester is a good reflection of embryonic growth and therefore of vascular adaptation in the first trimester of pregnancy. Differences in growth between embryos from fresh transfers, frozen transfers, and spontaneous pregnancies are visible early on, as early as the first trimester.

The hypotheses put forward to explain these differences include the secretion of relaxin by the corpus luteum, which is present in the natural cycle but not in the substituted cycle. This hormone plays a role in cardiovascular and renal adaptation to pregnancy in the first trimester. Low levels of relaxin would therefore be associated with poorer cardiorenal adaptation in the first trimester and thus with greater vascular risks in late pregnancy.

Inclusion Criteria:

• Primiparous women
• Intra-couple ART
• Of childbearing age undergoing assisted reproductive technology (18 to 44 years and 11 months)
• Who underwent a fresh or frozen embryo transfer during the inclusion period resulting in a progressing monofetal pregnancy (ultrasound showing an embryo with cardiac activity).
• Able to understand the ins and outs of the study
• Having indicated their willingness to participate in the study

Exclusion Criteria:

• Uterine pathologies (adenomyosis, fibroids)
• Multiple pregnancies
• Spontaneous pregnancy
• Pregnancy through gamete donation
• Refusal to undergo obstetric ultrasounds
• Subject participating in interventional research involving an exclusion period still ongoing at the time of pre-inclusion

This study will focus on patients who underwent fresh or frozen embryo transfer in the Reproductive Medicine Department and were monitored at the Women's and Children's Hospital, resulting in a progressive pregnancy with first trimester ultrasound.