Screening for genetic defects

Screening women with blood tests and ultrasound during the first trimester of pregnancy improves the detection of two serious congenital disorders affecting the baby. Down's syndrome, or trisomy 21, and Edwards' syndrome, also called trisomy 18, are genetic disorders that result from having an extra chromosome. A prime feature of both disorders is severe mental retardation. Both the syndromes are typically screened for during the second trimester of pregnancy. However, with such screening only 65 percent of abnormal pregnancies are detected. In five percent of cases such testing falsely indicates a problem when, in reality, everything is okay. Researchers form the Drexel University College of Medicine in Philadelphia, USA, used blood tests and ultrasound to screen 8,216 pregnant women during the first trimester.

It was found that the first trimester approach detected at least 79 percent of the pregnancies involving a baby with Down's syndrome. The approach was even better at detecting Edward's syndrome - 91% of affected pregnancies were identified. For both syndromes, the approach worked best among mothers who were at least 35 years of age. In fact, in these women, the early testing did not miss any of the babies with Edward's syndrome. The first trimester screening offers patients greater privacy, earlier results, and safer reproductive alternatives than the second-trimester screening method. However, until more research confirms this, the researchers propose that second-trimester screening should continue to be the standard of care.

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