The prospective study published in Molecular Cytogenetics investigated 1048 twin pregnancies over four years at the Maternity and Child Health Hospital of Anhui Province, China. The researchers analysed cell-free fetal DNA from pregnant women's peripheral blood and screened it to detect prenatal chromosomal abnormalities. However, there is limited evidence on NIPT effectiveness in twin pregnancies.
'The superior performance of NIPT in singleton pregnancies is recognised as an almost perfect screening method, which makes the medical community and the public hopeful that the test technology can be equally applicable for pregnant women with twin pregnancies,' wrote the authors.
The cell-free fetal DNA was sequenced and results that showed a high risk of chromosomal abnormality were subject to traditional karyotyping. Negative NIPT outcomes were followed up 42 days after delivery. Out of 1048 twin pregnancies, NIPT identified 13 cases of chromosomal abnormalities – two cases of trisomy 21, one case of trisomy 18, seven cases of aneuploidy in the sex chromosomes, one case of microdeletion and two cases of microduplication.
However, only two NIPT positive results were confirmed by karyotyping – one case of trisomy 21 and one of microdeletion. No false negatives cases were identified during the follow up. Therefore, the combined positive predictive value of NIPT was only 15.4 percent in twin pregnancies. Nevertheless, this is the first prospective study in which NIPT simultaneously detected autosomes and sex chromosome aneuploidies, microdeletions and microduplications as well in twin pregnancies.
'When NIPT results are inconsistent with karyotype results, clinicians should be patient in the process of interpretation,' the authors warned, adding that clinicians should reasonably guide high-risk pregnant women to verify the result by additional prenatal screening methods.
This study did not further clarify the cause of false-positive results so the conclusions still need further confirmation with more positive clinical pregnancy twin data.