Our recent publication in AJOG MFM was focused on studying the positive predictive value of the NIPT in pregnancies conceived after IVF and PGT-A. While this may seem redundant if the NIPT detects an aneuploidy that is later confirmed via diagnostic testing (which was not identified on PGT-A) this second round of screening adds important value. The generalized use of NIPT results in embryos created via IVF and PGT-A often being tested twice, once directly via PGT-A and then again through screening of cell-free fetal DNA in the NIPT. The NIPT has undergone multiple clinical validation studies. The NIPT can use either whole genome sequencing or targeted sequencing using SNPs on the chromosomes of interest. How high that fraction is can affect the sensitivity of the test. One difference is that the NIPT is actually looking at a ratio of maternal and placenta cfDNA known as the fetal fraction. For the NIPT, DNA fragments are analyzed that are released from the placenta into the maternal circulation as the cytotrophoblast and syncytiotrophobalst cells undergo physiologic cycles of fusion and apoptosis. What is happening between those two time points really remains unknown. So a lag exists between what we can reasonably test from the time point of a blastocyst and make a decision about transferring an embryo to the time point of development where prenatal screening is performed (around 10 weeks). We are also often faced with mosaic or segmental results that later are not confirmed on prenatal diagnostic testing like amniocentesis. The majority of the PGT assays on the market have not undergone validation studies using a nonselection trial. However, we know that this is not always the case especially depending on which PGT assay is being utilized. ![]() First, PGT-A operates under the assumption that the 5-10 trophectoderm cells that are sampled are ultimately going to be representative of the genotype of the baby. There are several differences between the NIPT and PGT-A that need to be considered when interpreting these tests sequentially. Women who have undergone a euploid embryo transfer are inherently a lower risk population for fetal aneuploidy, nevertheless they will be offered NIPT screening as recommended. Importantly, this encompasses women who have undergone IVF with PGT-A. ![]() Therefore, the major OB societies recommended the NIPT be made available to all pregnant women regardless of their risk status. However, when the diagnostic performance of the NIPT in the general OB population was compared to other prenatal screens, false positive rates were found to be significantly lower. Initially the NIPT was used for women at high risk for having a fetus with trisomy 21, 18 or 13. The test analyzes cell-free DNA fragments from maternal circulation, and is generally performed around 9-10 weeks as that is when concentrations are high enough for detection. The NIPT is a blood test for pregnant women that is used to screen for fetal aneuploidies. Non-invasive prenatal testing (NIPT) is recommended by American professional societies (ACOG, SMFM) to be offered to all pregnant women.
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