Abstract
Estimating the fetal fraction of DNA in a pregnant mother’s blood is a risk-free, non-invasive way of predicting fetal aneuploidy. It is a rapidly developing field of study, offering researchers a plethora of different complementary methods. Such methods include examining the differences in methylation profiles between the fetus and the mother. Others include calculating the average allele frequency based on the difference in genotype of a number of single-nucleotide polymorphisms. Differences in the length distribution of DNA fragments between the mother and the fetus as well as measuring the proportion of DNA reads mapping to the Y chromosome also constitute fetal fraction estimation methods. The advantages and disadvantages of each of these main method types are discussed. Moreover, several well-known fetal fraction estimation methods, such as SeqFF, are described and compared with other methods. These methods are amenable to not only the estimation of fetal fraction but also paternity, cancer, and transplantation monitoring studies. NIPT is safe, and should aneuploidy be detected, this information can help parents prepare mentally and emotionally for the birth of a special needs child.
Highlights
Screening for fetal aneuploidy or other fetal genetic defects are an important part of prenatal testing
If we find that the DNA fragments coming from chromosome 21 in the blood sample are significantly larger than 1.56%, we can infer fetal aneuploidy
The two drawbacks are that only male fetuses can be tested and that the small size of the Y chromosome can lead to high variation in measurements [63]
Summary
Screening for fetal aneuploidy or other fetal genetic defects are an important part of prenatal testing. The greater the maternal weight, the lower the FF This is because with a larger body mass index (BMI), the mother will shed more maternal DNA into the blood stream, in effect decreasing the proportion of cffDNA. A study by Lee et al [23] of 5625 singleton pregnancies showed that IVF-induced pregnancies had a median FF of 10.3% as opposed to a median value of 11.9% in spontaneous pregnancies, across MA, GA, BMI, and ethnicity This increases the false-negative rate of detecting aneuplodies in IVF-mediated pregnancies [24]. False negative; fetus appears normal when really affected Helps tell difference between maternal and fetal DNA Increases fetal fraction Decreases fetal fraction Falsification of fetal sex Apparently higher FF False positive; fetus appears to be affected Lowers fetal fraction False positive; extra twin’s DNA gives appearance of fetal aneuploidy
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