Application of noninvasive prenatal genetic testing in screening for chromosome abnormalities in pregnant twins
Objective To explore and analyze the application value of noninvasive prenatal genetic testing technology in screening for chromosome abnormalities in pregnant twins.Methods From December 2022 to December 2023,200 pregnant women with twin pregnancies who received non-invasive prenatal genetic testing screening in our hospital were selected as subjects of this study.Peripheral blood samples of the subjects were collected and prospective studies were conducted.Age,gestational age,chorionic sex,pregnancy mode and non-invasive prenatal genetic test results,clini-cal karyotype,delivery mode and pregnancy outcome were recorded and analyzed.Results ①The results of noninvasive prenatal genetic testing showed that there were 3 cases of chromosome abnormality in pregnancy twins,1 case of trisomy 21-high risk(T21),1 case of trisomy 18-high risk(T18)and 1 case of microdeletion each.The 3 cases of positive detection received amniotic fluid puncture,and the puncture results confirmed that 1 case was true positive,the type of chromosomal abnormality was microdeletion,and the other 2 cases were confirmed as false positive.It was calculated that the combined positive predictive value(PPV)of noninvasive prenatal genetic testing to screen for chromosome ab-normalities in pregnancy twins was 33.33％(1/3).②The combined positive predictive value of non-invasive prenatal genetic testing screening for microdeletions was 100％(1/1).③Analysis of follow-up results:the pregnant women who were confirmed to be true positive for chromosome abnormality in twin pregnancy chose reduction surgery after com-munication,and the two pregnant women who were confirmed to be false positive did not do other intervention,and gave birth after full-term pregnancy,and the newborn phenotype was not abnormal.A total of 189 pregnant women,95.94％(189/197),with full-term pregnancy and delivery of twins with obvious normal phenotype were followed up for 197 pregnant women with low risk due to non-invasive prenatal genetic testing results.There were 6 cases of ad-verse pregnancy outcomes,accounting for 3.05％(6/197),but none of the 6 cases of adverse pregnancy outcomes showed any characteristic intellectual impairment or chromosomal abnormalities(details of adverse pregnancy outcomes:2 premature births,2 low birth weight infants,1 umbilical hernia,1 polycystic kidney).There were also 2 cases of a-bortion,accounting for 1.02％(2/197).④Analysis of the causes of false positive results of noninvasive prenatal genet-ic testing:relevant studies have shown that the main causes of false positive results in the screening of pregnant twins with this technology include maternal tumors,chromosome copy number variation and restrictive placental mosaism.⑤One case of trisomy 21-high risk(T21),one case of trisomy 18-high risk(T18)and one case of trisomy 13-high risk,and one of the twins was T21 after chromosome karyotype examination;The remaining 197 pregnant women showed low risk and no abnormal karyotype.The results of non-invasive prenatal genetic testing showed that the positive rate of ART was 3.16,the false positive rate was 1.05,the sensitivity was 100％,the specificity was 99％and the detection rate was 100％.Serological screening(1∶1000～1∶270)positive rate was 1.10％,sensitivity,specificity and detection rate were 100％;The positive rate of age ≥35 years old was 7.69,and the sensitivity,specificity and detection rate were 100％.There were no missed cases,no positive cases in T18 and T13,and T21 were correctly identified and test-ed.Therefore,if the screening results of non-invasive prenatal genetic testing are inconsistent with the results of am-niocentesis,medical workers should also do a good job of pacification and explanation for pregnant women and their fami-lies,and it should also be combined with other test results to reasonably guide pregnant women at high risk of chromo-some abnormalities to perform amniocentesis to further clarify whether there are abnormalities.Conclusion As a screen-ing technique,the positive predictive value of noninvasive prenatal genetic testing in pregnant twins with chromosome ab-normalities is limited,and the screening effect is not ideal,and this technique should be carefully selected in the screen-ing of pregnant twins with chromosome abnormalities.
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