Significant progress has been made in trisomy 21 (T21) screening, which has been well regulated in France since 1997, with a maternal serum marker (MSM) screening rate of around 80%. Non-invasive prenatal screening (NIPS) has proved its worth, particularly in women at increased risk of trisomy 21 by MSM (excluding ultrasound call signs).
In France, the decree of December 14, 2018 (JO of December 20, 2018) modified the rules of good practice for prenatal screening and diagnosis of trisomy 21.
Maternal serum markers
All pregnant women, whatever their age, are informed during a medical consultation of the possibility of undergoing combined first-trimester screening combining ultrasound measurements (Cranio-Caudal Length or CCL, Nuchal Clarity or NC, and ultrasound date) with first-trimester maternal serum markers (Pregnancy-Associated Plasma Protein-A or PAPP-A and hCGß). Sampling is carried out between 11 weeks and 0 days and 13 weeks and 6 days of amenorrhea (i.e. for a LCC of between 45 and 84 mm). If combined screening cannot be performed (no ultrasound in the first trimester in compliance with the decree, or late blood sampling), screening will be performed using maternal serum markers during the second trimester only (total hCG or hCGß, and AFP +/- estriol). Sampling is performed between 14 weeks and 0 days of amenorrhea and 17 weeks and 6 days of amenorrhea. Integrated sequential risk testing combining biochemistry and ultrasound is no longer possible.
If the risk of maternal serum markers previously performed is between 1/51 and 1/1000, the patient is offered an lncT21 DNA screening test. An ADNIcT21 screening test may also be offered to the patient without using the maternal serum marker step in the following situations: twin pregnancies, history of pregnancy with T21, or a parent carrying a Robertsonian translocation involving a chromosome 21. The JO of December 27, 2018 defines the coverage of lncT21 DNA (acts 4087 and 4088 of the NABM) and came into force on January 17, 2019.
Foetal rhesus D genotyping
Prenatal determination of foetal RHD genotype, based on the principle of the existence of foetal DNA circulating in maternal blood, is performed using a real-time PCR technique. This analysis has been listed on the NABM since July 13, 2017 and is fully reimbursed.
Prescription is reserved for rhesus D-negative pregnant women from 11 SA.
The test’s contribution to the management of rhesus D-negative pregnant women is important insofar as the presence of a baby who is also rhesus D-negative avoids the need for prophylactic treatment in non-alloimmunised patients and enables a significant reduction in follow-up in alloimmunised pregnant patients.