927: Prenatal diagnosis of genetic abnormalities: Has it really moved to the first trimester?

Abstract

Advances in genetic screening can identify patients at high risk for common genetic conditions early in pregnancy, and can facilitate early diagnosis and abortion. Less common abnormalities might only be diagnosed when invasive testing is performed after structural abnormalities are identified. Our objective was to compare gestational ages at diagnosis and abortion for genetic abnormalities identified based on screening and other genetic abnormalities. All prenatal diagnostic procedures in our department from 2012-2017 were reviewed, and singleton pregnancies terminated following diagnosis of genetic abnormalities were identified. Cases diagnosed as the result of screening tests were compared to remaining cases. Specific conditions were considered “screened for” if they can be suspected by NIPT, biochemistry, carrier screening, or if the patient was a known carrier of a single gene disorder. Since abnormal NT is associated with many genetic disorders, abnormal karyotype, microarray, or Noonan syndrome associated with abnormal NT were considered “screened for”. Gestational age at abortion was the primary outcome. Fisher's exact test and Mann-Whitney U were used for statistical comparison. 267 cases were included. 230 (86%) of abortions were performed for genetic disorders considered screened for, with 209 (91%) of these for karyotype abnormalities, 9 (4%) for microarray abnormalities and 12 (5%) for single gene disorders. 37 (14%) of abortions were performed for conditions not included in screening or with any family history, with 12 (32%) of those for karyotype abnormalities, 18 (49%) for microarray abnormalities and 7 (19%) for single gene disorders. Invasive testing and abortion occurred at earlier median gestational age for those with conditions that were screened for: 12w2d vs. 15w5d; p =<.001, and 13w5d vs. 20w0d; p=<.001. (Table 1) Most abortions were for common chromosomal abnormalities and single gene disorders that can be suspected early in pregnancy. About 1 in 7 were performed for less common conditions in patients not known to be at risk. Because many structural abnormalities associated with rare genetic conditions will not be identified until the second trimester, prenatal diagnosis and abortion occurred significantly later. Physicians and patients should be aware of the limitations of genetic screening, particularly when restrictions in abortion access can limit options in the second trimester.