|Prenatal tests: Screening after conception|
|Prenatal tests: Screening after conception|
These tests help screen for genetic and other developmental defects before your baby is born:
- Amniocentesis. This test, the leading method for finding genetic abnormalities, is usually given between the 14th and 20th weeks of pregnancy. It is commonly administered to pregnant women 35 and over. During the test, a sample of the amniotic fluid is drawn and analyzed.
- Chorionic villus sampling (CVS). In CVS, a syringe draws out a few of the tiny hair-like projections (the “villi”) that are part of a developing placenta. The test was developed to detect genetic defects earlier in pregnancy than amniocentesis. CVS is usually performed in the 10th week of pregnancy.
- Alpha-fetoprotein test. This blood test, given between the 15th and 20th weeks of pregnancy, measures the level of a protein produced by the fetus. An unusually high level may indicate a neural tube defect, such as spina bifida, while a low level may indicate Down syndrome.
- Ultrasound exam. Performed as early as six to eight weeks after a woman’s last period, this painless, noninvasive test monitors the growing fetus. Among other things, it can reveal the baby’s age and size and may indicate abnormalities.
As medical technology moves forward and more and more prenatal problems are able to be treated while the baby is still in the womb, prenatal testing will become increasingly valuable.
What could be more reassuring to prospective parents than learning that their growing child is healthy? More often than not, prenatal tests offer expectant moms and dads just that type of reassurance (see sidebar). And today’s screening techniques go one step further: Genetic counseling can now help couples assess their chances of passing on a hereditary disorder to their child before conception takes place.Not for every couple
Is genetic counseling a good idea for every man and woman still in the planning stages of pregnancy? Not necessarily. However, you and your partner may be good candidates if…
Preconception screening: What’s available
- You’re 35 or over. Why? The older you are, the greater your risk of carrying a baby with Down syndrome. According the National Down Syndrome Society, at age 25, for example, the risk of conceiving a child with Down syndrome is one in 1,000. At age 35, it rises to one in 400, and at age 45, it soars to one in 35.
- You suspect that you (or your partner) may be carrying a gene for Tay-Sachs, sickle cell anemia, cystic fibrosis, hemophilia or another genetic disorder.
- You have already given birth to a child with a genetic defect.
- You have a child or a close relative who is mentally retarded.
- You’re concerned about exposure to radiation, infections, chemicals or other hazards.
- You have a history of miscarriages or stillbirth.
Even though experts believe most of us carry a few abnormal genes, those “bad” genes usually are outweighed by normal ones. That favorable ratio accounts for the low incidence of genetic disorders. Also accounting for the low rate is the fact that many genetic disorders are recessive. That means both parents must carry—and pass on—a faulty gene for their child to be affected.
Recessive disorders for which preconception screening is available include:
Sickle cell anemia. Those who suffer from sickle cell anemia have an increased susceptibility to serious infections such as pneumonia. About one out of every 10 African-Americans carries a gene for sickle cell anemia. Some Hispanics and people of Caribbean ancestry also carry the gene.
Cystic fibrosis. About one in every 25 Caucasian Americans carries a gene for cystic fibrosis, a severe disorder in which mucus builds up in the respiratory system and the pancreas.
Thalassemia. This inherited disorder takes several forms, some of which cause severe anemia and may require frequent blood transfusions. People of Mediterranean and Asian ancestry are at greatest risk for this condition.
Hemophilia. This disorder of the blood’s clotting mechanism is usually passed from a healthy female carrier to her son.
Tay-Sachs disease. Expectant parents of eastern European Jewish ancestry may be carriers of the gene that causes Tay-Sachs disease. Babies born with this condition lack an enzyme that keeps fat from accumulating in the brain’s nerve cells. Most children with Tay-Sachs die before age 5.If you suspect you’re a candidate…
See your doctor for an evaluation. During your visit, be prepared to answer questions regarding the medical history of your parents, siblings, aunts, uncles, cousins and grandparents. Do any of those family members have an inherited disease? Have any of them died of a rare or unusual condition? Are any affected members of your immediate family close relatives, such as first cousins? What is their ethnic origin?
Answers to those and other questions will help your doctor determine whether you need further counseling by a geneticist. If you are referred for further testing, remember this: Only 5 percent of those seeking genetic counseling for a specific disorder turn out to have a problem. That said, the odds of conceiving a healthy baby are already in your favor.