Losses of imprinting are involved in various syndromes. Those occurring in the 11p15 region lead to Beckwith-Wiedemann and Silver-Russell Syndromes. These losses of imprinting follow a mosaic pattern, rendering their detection difficult, especially given the scarcity of available DNA in amniotic fluid. Thus, in spite of growing demand, prenatal diagnosis (PND) for imprinting abnormalities of the 11p15 region is not available.

The recent development of a quantitative PCR method that permits the methylation index (MI) of imprinted regions to be calculated renders PND technically possible. Nevertheless, because of the mosaic nature of these anomalies, it is essential to verify that the methylation pattern of the 11p15 region obtained from the amniotic fluid matches that obtained from the blood.

To evaluate the agreement between the methylation index of the 11p15 region obtained using DNA extracted from amniocytes and that extracted from cord blood leukocytes, by calculating the intraclass correlation coefficient (ICC).

Ancillary study :

This second part of the study aims to determine the standard of methylation index of the 11p15 region (inclusion of 100 additional patients). The use of amniotic liquid will allow to calculate :

• the average of methylation index,
• the value of the standard deviation
• the inter-assay coefficient of variation for the test-used.

Inclusion Criteria:

• Pregnant women, 18 years of age or older
• Requiring amniotic fluid sampling in the context of pregnancy care after 15 weeks of amenorrhea
• Having provided written informed consent
• Followed at Trousseau Hospital or Clinique des Bluets during their pregnancy
• Covered by or beneficiary of a state health insurance program (except for medical aid programs)

Exclusion Criteria:

• Warning signs on ultrasound that require a medical termination of pregnancy to be discussed even before amniocentesis is performed