Preeclampsia (PE) is a major obstetric complication with short- and long-term consequences for the mother and the fetus. Early screening tools to reduce its mortality and morbidity, as well as to prevent the life-threatening consequences are needed. Thus, the detection of women at risk of suffering PE is key to apply preventive and treatment strategies. Recently, the maternal contribution to PE based on defective decidualization that prevents the establishment of a functional maternal-fetal interface has been evidenced. The main objective of this study is to identify molecular markers or aberrant maternal-fetal cell types that can be detected early in the development of the disease in maternal-fetal interface tissue (chorionic villi + decidua) collected during gestational weeks 9 to 15. Maternal-fetal interface biopsy will be collected from women who have a recommendation for aneuploidy testing. The remaining fragment will be used for this study.

The hypothesis is that those women who develop PE have impaired decidualization associated with shallow cytotrophoblast invasion during the development of the maternal-fetal interface whose molecular profile analysis at the single cell level will allow characterization of PE development prior to the onset of symptoms.

The purposed study is a biomedical, prospective, multicentre, case-control aimed to characterize the molecular profile of the maternal-fetal interface in the first trimester of pregnancy early in the development of preeclampsia using single-cell sequencing technology. Distinguishing the maternal and fetal origin of the chorionic biopsy cells, describing the maternal-fetal interface and deciphering the intercellular communications and altered pathways in PE and other obstetric complications could be suggested as a secondary outcome, as well as the characterization of the blood sample, the epigenome and metabolome of single cells or the validation of markers of the different cell types. Another objective will be to perform a molecular characterization of maternal-fetal blood and tissue samples collected at the time of delivery, with the aim of correlating the alterations detected in the first trimester with the molecular profiles at the end of pregnancy in both PE patients and controls.

Subjects will be 2084 pregnant women over the age of 18 recruited between 9 and 15 gestational weeks. Patients attending the participating referral centers for a chorionic villus biopsy due to the detection of a foetal chromosomal abnormality risk will provide the leftover chorionic biopsy sample after determination of the risk of trisomies and a peripheral blood sample for genotyping of maternal lymphocytes and circulating cRNA.

Data will be registered in an electronic Case Report Form (eCRF) specifically designed for this study. Monitoring activities and data verification will be performed during the whole study to ensure data quality, integrity and transparency.

The total estimated duration of the study is 52 months, of which the first 48 months will correspond to the recruitment period of the participants.

Inclusion Criteria:

• Patients whose written informed consent approved by the Ethics Committee (EC) has been obtained, after having been duly informed of the nature of the study and voluntarily accepted to participate after being fully aware of the potential risks, benefits and any discomfort involved.
• Women over the age of 18 at the time of signing the informed consent form.
• Pregnant women with a single gestation between weeks 9 and 15 of gestation who will undergo a chorionic villus biopsy according to the centre's usual clinical practice.

Exclusion Criteria:

• Women with multiple pregnancy.
• Non-evolving pregnancies (including delayed abortion/foetal orbit).

Pregnant women over 18 years old

Pregnant women over the age of 18 recruited between 9 and 15 gestational weeks who attend the participating referral centers for a chorionic villus biopsy due to the detection of a foetal chromosomal abnormality risk.