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The frequency of IUGR is between 3 and 10% of births. The etiologies and mechanisms of IUGR are multiple. The placental insufficiency, that is the defect of perfusion, is, however, the principal mechanism, far in front of other maternal or fetal causes. This placental insufficiency is also now recognized as an essential risk factor for cardiovascular and metabolic diseases, such as diabetes, in adulthood. The interest in understanding in utero development is thus further increased by the short-, medium- and long-term consequences of placental dysfunction. However, there are few ways to evaluate uteroplacental vascularization in vivo. MRI is an imaging technique used routinely in the exploration of the fetus in addition to ultrasound. Its safety on the fetus and the mother is largely demonstrated at 1.5T. There are also MRI sequences used daily in the clinic to evaluate perfusion and organ structure in children and adults (brain, kidney, heart, etc.). Their application for evaluation of perfusion and placental structure, although still confined to research, is very promising. The investigator's team has extensive experience, in animals or in children, in the use of these sequences that could be used to evaluate placental function in vivo. The ASL (Arterial Spin Labeling) in particular is the most encouraging functional imaging technique because it allows today to measure an organ blood flow quantitatively and without injection of contrast medium.

The inclusion will take place at the earliest at 20 weeks after the completion of the standard morphological ultrasound of the 2nd trimester (carried out at 20-24SA) and at the latest at 35 SA, within the framework of one of the 2 clinical subgroups of patients considered (high risk and low risk).

The objectives of this study will be achieved by the prospective setting up of a LUMIERE cohort on PLACENTA.

Inclusion Criteria:

• Singleton pregnancy without fetal malformation seen on ultrasound. Group 1: High risk IUGR patients

  • EPF<10th perc or PA<10th perc and Doppler ombilical IP> 95th percentile,
  • EPF or PA<3th perc reference curves from Collège Français d'Echographie Fœtale, between 20 et 34 GW,

Group 2: Low risk IUGR patients

• EPF et PA>20th perc reference curves from Collège Français d'Echographie Fœtale, between 20 et 34 GW

Exclusion Criteria:

• - Contraindication to MRI
• Impossible subsequent follow up
• Maternal status contraindicates continuation of pregnancy
• Participation in another search
• "Protected" patient

Pregnant patients with low and high risk of placental IUGR followed in the Fetal Medicine Department of the Necker-Enfants Malades hospital.