Prenatal tests that screen for fetal anomalies identify small groups of pregnant women who are more likely to have a baby with a specific birth defect. Screening tests can only give a probability or risk that a specific condition is present; they cannot give definitive answers. They are given to most pregnant women. Prenatal diagnostic tests are procedures such as amniocentesis, chorionic villus sampling ( CVS ) that can tell definitively if a fetus has the chromosomal defects or genetic disorder. Since diagnostic tests are invasive and involve a risk of miscarriage they are usually done only on women who had positive screening tests, or on those who have a higher risk because of their age or other risk factors. Screening usually involves finding out the mother’s age and family medical history. Jewish women of Ashkenazic descent are likely to have a child with Tay-Sachs, Canavan’s disease, or Gaucher’s disease. African-American women are more likely to have a baby with sickle cell anemia, and Italian women have a greater risk of having babies with thalassemia. These women (and their husbands) can be screened to see if they are carriers of these diseases.
Today’s topic is CVS I’d asked Dr. Rochan, a perinatologists from NYU to give us an update on CVS .
Introduction:
Chorionic Villus Sampling ( CVS ) is a prenatal diagnostic technique performed between 10 and 14 weeks to determine fetal karyotype and genetic disorders for which testing is available. Currently, we have many options to these parents including selective mating, donor sperm or donor eggs, pre-implantation genetic diagnosis (PGD), and genetic ultrasound, amniocentesis and CVS . The perception of the potential quality of life and the burden of an illness for an affected offspring as well as legal considerations, such as wrongful birth are common issues for patients and physicians.
The advantage of prenatal testing includes the possibility of terminating pregnancy, as well as early referral to hospitals that could provide pediatric surgery, level 3 neonatal intensive care units, consultation with neonatologist and other pediatric medical and surgical sub specialist, better guidance, planning, more focused obstetrical care and better decision-making possibilities for the patient.
As maternal age increases, the risk of aneuploidy, due to nondysjunction of the chromosomes, rises. At 35, the risk of Down syndrome is 1 in 378. At age 40, the risk of Down syndrome is 1in 106. At age 45, the risk of Down syndrome is 1 in 30 and the risk of all chromosomal problems is about 1 in 21. There are screening tests available such as first trimester, second trimester testing to the risk of Down syndrome and Trisomy 18.
History of CVS :
First, CVS was performed by the Chinese in 1972 for fetal sex determination without ultrasound guidance. In 1980, ultrasound was first used to perform CVS . Depending upon the location of the placenta, CVS could be performed transvaginally or transabdominally. If it is performed transvaginally, a full bladder is required.
Complications of CVS include among others vaginal bleeding and spotting. In addition, rupture of membranes is reported in about 0.3%. The overall risks of miscarriage depends on operator experience and varies from 1 in 100 to 1 in 400. Of note, the same risk of miscarriage is recorded for singletons and twins. The major advantage of CVS over amniocentesis is early diagnosis; this helps lower maternal anxiety much earlier and affords improved bonding to the pregnancy in the second trimester. In the case of a fetus with aneuploidy, CVS makes possible and easier and more private first trimester pregnancy termination, if the patient so chooses. Genetic counseling is important and should be done prior to every invasive procedure. Family history, the outcomes of prior pregnancies and a genetic history should be obtained. Patients from Ashkenazi Jewish descent should be encouraged to undergo Ashkenazi Jewish testing. From other caucasians, cystic fibrosis and fragile X testing are recommended. For Asians, African-Americans and patients of Middle Eastern descent, MCV and hemoglobin electrophoresis are also recommended.