Health Editor’s Note: Like it or not, some” soon to be parents” choose to know if their newly forming fetus will have genetic defects, such as those which are caused by abnormalities in the sex chromosomes, either extra chromosomes (Down syndrome, Patau syndrome, and Edwards syndrome) or a missing part of a chromosome as well as single gene mutations.
Previous ways to obtain fetal cells for chromosome/genetic testing have been to obtain fetal cells from the amniotic fluid (sac and fluid which surrounds the developing fetus) by obtaining a small sampling with the use of a needle. This process is called amniocentesis. Another procedure is chorionic villus sampling (which is taking a sample, also using a needle either through the mouth of the mother’s uterus or through the abdominal wall, of the placenta [organ with develops on the inside of the uterus after the embryo has implanted and where the baby is attached by the umbilical cord through which oxygen and nutrients flow in the mother’s blood to the developing fetus]. It is easy for you to imagine that either of these procedures carry the potential of harm to the fetus and the possible end of the pregnancy.
Simply taking blood from the mother can show DNA results for the fetus since there are fetal blood cells circulating in the mother’s blood stream. There is also the added result of sequencing the mother’s DNA at the same time. There are some disclaimers that go along with this testing, which presents no potential harm to the fetus while obtaining the fetal DNA. I would also suspect that the cost for maternal blood/fetal DNA sequencing would be less costly than amniocentesis and chorionic villus sampling…..Carol
Fetal DNA sequencing potentially could reduce need for invasive prenatal diagnostic procedures
NIH review article also describes need for practitioner education in interpreting results of genetic tests.
What
Sequencing the fetal DNA that circulates in a pregnant woman’s blood holds promise for modern genomic medicine, according to a review article by Diana W. Bianchi, M.D., a senior researcher and institute director at the National Institutes of Health, and her colleague. Fetal DNA sequencing improves the accuracy of prenatal screening tests for genetic conditions and at times has led to the diagnosis of maternal conditions that may have otherwise gone undetected. The article appears in the New England Journal of Medicine.
The blood test analyzes fetal DNA that enters a pregnant woman’s blood from her placental cells. It most commonly is used to screen for fetal disorders resulting from an extra chromosome: Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome). It also has been used to detect conditions resulting from an extra sex chromosome, from a missing part of a chromosome, and even for conditions resulting from a single gene mutation. Among women who test negative for any abnormalities, cell free DNA sequencing may reduce the need for additional prenatal testing procedures, some of which may increase miscarriage risk. The American College of Medical Genetics and The American College of Obstetricians and Gynecologists caution that patients and their clinicians should know that fetal DNA sequencing is a screening test and not a diagnostic test. Confirmatory testing should continue to be offered to women with positive results. The authors also note that at present, no fetal DNA sequencing tests have been reviewed by the FDA to evaluate their analytical and clinical validity or performance claims, and the validity of the results may vary from lab to lab.
Because maternal DNA is also in the blood sample, it is sequenced along with fetal DNA, which may lead to the detection of conditions in the pregnant woman, including blood abnormalities and sex chromosome abnormalities. The growth of DNA testing and its rapid incorporation into medical care has identified a need for more genetic education and consideration of the ethics of expanded prenatal testing, the authors conclude.
Who
Diana Bianchi, M.D, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and head of the Prenatal Genomics and Therapy Section of the Medical Genetics Branch of NIH’s National Human Genome Research Institute.
Article
Bianchi, DW and Chiu, RK. Frontiers in Medicine: Sequencing of circulating cell-free DNA during pregnancy New England Journal of Medicine. 2018
About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): NICHD conducts and supports research in the United States and throughout the world on fetal, infant and child development; maternal, child and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit NICHD’s website.