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Abnormality Tests in Pregnancy

Jul 1, 2010 | By Walli Carranza
Abnormality Tests in Pregnancy
Photo Credit pregnancy on red image by starush from Fotolia.com

Imagine a time when the health of your child was a complete mystery until the day of delivery.
Amniocentesis was first developed in the late 1950s as a way of determining the sex of a child but was not used until the 1970s for the diagnosis of fetal anomalies such as Down syndrome. Today, pregnant women are offered non-invasive opportunities for screening in the first and second trimesters as well as amniocentesis, when indicated.

First Trimester Testing

Fetal assessment should be offered at 11 to 14 weeks to all pregnant women, according to the American College of Obstetricians and Gynecologists. This process includes a blood test to measure levels of two pregnancy-related hormones and an ultrasound to measure the thickness of the fetus' neck. This is referred to as a test of nuchal translucency. A fetus with Down syndrome or other chromosomal abnormalities commonly has increased thickness at the back of the necks because of an increased amount of lymph tissue that accumulates in that area.
The results of the nuchal translucency screening, combined with those of the blood tests, plus the mother's age are used to assess the risk of fetal anomalies.
In the first trimester these combined tests will accurately detect Down syndrome in approximately 85 percent of cases, according to data published by the Mayo Clinic Laboratories. The detection of other chromosomal abnormalities is slightly less reliable.
It is important to remember that first trimester screening are screening tools. Before birth only amniocentesis is able to accurately diagnose the presence of a chromosomal abnormality.

The Second Trimester Quad Screen

When a woman is between 15 and 20 weeks of pregnancy, the American College of Obstetricians and Gynecologists recommends that obstetricians offer all pregnant women four blood tests performed from a single sample of blood. These are designed to detect the possibility of a chromosomal abnormality or an opening in the body, either at the spine or in the abdomen.
When all four second trimester blood tests are done this test accurately predicts 80 percent of fetuses with Down syndrome.
Many women, especially those under 35, choose to have both first and second semester testing done and base their decision to proceed to amniocentesis, an invasive test, on these screening tools.
Down Syndrome and the other chromosomal abnormalities cannot be cured but second trimester screening can detect the possibility of treatable open neural tube defects, such as spina bifida, with 80 percent accuracy. When this finding is confirmed by ultrasound a Cesarean section is often scheduled to avoid injury to the spine. The opening is then closed soon after delivery.

Amniocentesis

Amniocentesis, the removal of a small amount of fluid from the sac that surrounds the fetus, is an invasive procedure that carries a 0.3 percent risk of fetal death or miscarriage. It is performed between 15 and 20 weeks of pregnancy and is capable of diagnosing almost 350 different fetal anomalies.
The American College of Obstetricians and Gynecologists revised its policy on amniocentesis in 2007, stating that all women should be offered the option of screening tests for Down syndrome and other fetal anomalies regardless of their age at the time of conception. This reverses the two-decade-old policy of recommending amniocentesis for all women over 35 years of age and for those whose screening tests indicate that a problem could exist.

What Prenatal Testing Can and Can Not Offer

Prenatal screening alerts the parents and their health care provider to the possibility that a fetal anomaly exists, Amniocentesis provides samples that, when analyzed, can diagnose a chromosomal disorder, like Down syndrome, with a high level of accuracy.
Knowing a child's status before birth allows mothers to decide whether they want to deliver in a community hospital or at a medical center hospital where specialists can deal with the medical and surgical needs of a high risk newborn. It also allows the family to prepare emotionally. They can gather information to help them meet their child's special needs and meet with other families coping with the same diagnosis. In addition, after confirming the diagnosis, some families elect to terminate the pregnancy.
Amniocentesis can diagnose a genetic disorder exists but it cannot tell parents where on the wide spectrum of potential the child with a disorder like Down syndrome will function or whether the child will be able to live independently. It also does not detect or predict autism, other developmental disabilities or behavioral health disorders.

Preimplantation Genetic Diagnosis

For couples who want to ensure that only healthy embryos are implanted, maternal-fetal specialists offer preimplantation genetic diagnosis. A woman's own eggs or a donor's eggs are harvested from the ovaries and fertilized externally. This procedure, used since the 1980s, is called in vitro fertilization. To test the genetic health of the conceived embryos an examination is made of a tiny piece of material discarded by the early stage embryo, called a polar body. Only an embryo free of detectable genetic anomalies is implanted.
Approximately 250 centers in the United States as of 2010 are offering preimplantation genetic analysis. Using this technique improves the rate of successful implantation compared to in vitro fertilization alone because healthy embryos have a better chance of implanting. It also eliminates the need, normally, to implant several embryos hoping one will survive, and, for most mothers, it replaces amniocentesis.

References

Article reviewed by Ecliptic Extremes Last updated on: Jul 1, 2010

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