In the plasma of any pregnant patient circulates DNA (also called circulating free DNA). The vast majority of this circulating free DNA is of maternal origin and about 10% is of fetal origin (fetal circulating free DNA). This percentage of fetal circulating free DNA (corresponding to the fetal fraction) increases with gestation.

The pathophysiological hypothesis of this research is that there is a change in the fetal fraction (FF) of fetal circulating free DNA in patients with autoimmune disease (AID). The underlying mechanism would be a massive release of maternal cfDNA responsible for a dilution of fetal cfDNA. This dilution of fetal cfDNA would result in a decrease in the estimate of the foetal fraction of circulating free DNA. However, when the foetal fraction of circulating free DNA is insufficient (4% most often), screening for Trisomy 21 (T21) by fetal circulating free DNA becomes uninterpretable (NC for "non-contributory" result), and cannot be used to assess the risk of T21. In this case, the dose of fetal circulating free DNA can be performed again after 15 days, as the amount of fetal circulating free DNA increases with gestation. In a small number of cases the result will remain NC.

As tests using DNA are becoming more widespread, it is important to prospectively evaluate the results of these tests in the population of patients with AID, which represents about 3 to 5% of pregnant women.

Circulating fetal DNA (cfDNA) in maternal blood is now routinely used for prenatal screening for Down syndrome 21 (T21). In about 1% of cases, the test result is not contributory (NC). The investigator's team recently found, in a retrospective study, an association between the existence of an autoimmune disease (AID) and a high risk of NC. However, this was only a subgroup analysis, requiring confirmation by a dedicated study. Tests using deoxyribonucleic Care (dNCare) are becoming more widespread, so it is important to prospectively evaluate the results of these tests in the population of patients with AID, which represents about 3 to 5% of pregnant women.

The main objective of this study is to compare the rate of NC in a population of patients with DIA to that of a population of patients without MAI when screened for T21 by the cfDNA study in the first trimester of pregnancy.

The secondary objectives are :

• To assess the performance of fetal cfDNA for T21 screening in the population of PATIENTS with AID and to compare them with performance in the non-auto immune disease population.
• To assess the performance of the combined first trimester screening for T21 screening and compare it with those of fetal cfDNA in the population of patients with AID.
• In patients with an NC result, analysis of the distribution of fetal fractions according to the presence and severity of maternal autoimmune pathologies. The distribution will be compared to that of the control population.
• To assess the association between fetal fraction and the occurrence of vascular complications of pregnancy in both groups with and without auto immune disease.

AFFEPI is a prospective multicenter, interventional, exposed/non-exposed cohort study

There are two group :

Exposed group: Any patient with a auto immune disease followed at one of the 14 centres who wants to be screened for T21.

Unexposed group: Patients who do not carry an auto immune disease identified at the interview (no history of auto immune disease; no symptoms suggestive of a auto immune disease).

Inclusion Criteria:

Patients in the exposed group:

• Single-fetal pregnancy with a term between 11 and 13-6 weeks of amenorrhea (SA) from spontaneous pregnancy or by medical assistance to procreation.
• Age ≥ 18 years
• Affiliated with a social security or beneficiary scheme
• Desire for natal screening of T21, not yet realized
• Patient with a condition on the following list: [see Chapter 7.2]

Patients in the unexposed group:

• Single-fetal pregnancy with a term between 11 and 13-6 weeks of amenorrhea (SA) from spontaneous pregnancy or by medical assistance to procreation.
• Age ≥ 18 years
• Affiliated with a social security or beneficiary scheme
• Desire for natal screening of T21, not yet realized
• No pathology that meets the list mentioned in the above section
• Clinically asymptomatic patient with no clinical symptoms suggestive of AID: arthralgias, skin or mucous disease, dry syndrome, Raynaud syndrome, purpura.
• Patient respecting frequency pairing

Exclusion Criteria:

• BMI > 35 kg/cm2
• Multiple pregnancy
• No first trimester ultrasound (between 11 and 13-6 SA)
• Screening for unwanted T21
• Patients already included in an interventional research protocol
• Morphological abnormalities on first trimester ultrasound and/or nucal clarity - 3.5mm
• Patient under the protection of justice

pregnant population