[Preliminary analysis of the cause for the failure of non-invasive prenatal testing using cell-free fetal DNA derived from peripheral maternal blood].

OBJECTIVE: To explore the cause of failure of non-invasive prenatal testing (NIPT) using cell-free fetal DNA from peripheral maternal blood.

METHODS: A total of 31 832 cases of NIPT were retrospectively analyzed. The clinical data of pregnant women were analyzed and the outcome of pregnancy was followed up.

RESULTS: Among the 31 832 cases, 200 patients have failed for the first NIPT test. Second test has succeeded in 171 (85.9%) of 199 cases, while 28 cases (14.1%) still yielded no effective results. This gave rise for a total failure rate of 0.088%. Of the 28 cases, 11 (39.2%) were due to high content of total free DNA and could not be sequenced, 17 (60.7%) were found to have the fetal DNA content of less than 4%. Among the 171 cases which have obtained a valid result, NIPT showed that there were 4 patients with high risk of trisomy 21, 18 cases with high risk of 18 trisomy and 1 case with high risk of 13 trisomy. Karyotyping analysis of the amniocytic chromosomes has identified 3 cases with 47,XN,+21, 1 case with 46,XN,rob(21;21), 1 case with 47,XN,+18, while the 13 trisomy case was found to be false positive. For the 28 cases with failed NIPT retest, 14 had normal delivery, with no anomaly noticed in the neonates. Nine patients had opted for artificial abortion during middle or late pregnancy due to maternal factors (4 cases) or fetal factors (5 cases). Four patients developed complications of pregnancy. One case was in good condition upon follow-up. Four cases were lost during follow-up. Of the 11 pregnant women who had failed the NIPT test due to high content of total free DNA, 6 (54.5%) had opted for artificial abortion during midterm pregnancy, which was significantly higher than that of pregnant women with low free DNA content (17.6%).

CONCLUSION: Failure of NIPT testing should attract attention from researchers. Failure of single NIPT test should not be regarded as a high risk signal for fetal chromosomal aneuploidies. For those where the test has failed again, genetic counseling and strengthened perinatal care should be provided for the pregnant women.