First trimester screening in pregnancy

Doctors can make a Down syndrome diagnosis for a baby while the mother is still pregnant. Down syndrome is caused by the presence of an extra 21st chromosome in the baby. In the past, mothers were given the choice of having tests to determine if their baby might have Down syndrome. Mothers over 35 are particularly at risk to have a Down syndrome baby. Today most mothers, especially mothers over 35, are strongly encouraged to have the first set of tests, called screening tests, to see if there is any risk of Down syndrome. This article discusses the types of screening tests that are available and the next steps an expectant mother should take if the screening tests indicate a Down syndrome diagnosis.

Knowing you have a healthy baby as early in your pregnancy as possible can significantly ease your worries and stress. And, if there is a problem, it’s better learning this early on, no matter what you decide to do about it. In the past, women had to wait until the second trimester to have an amniocentesis to test for Down syndrome. But in recent years, first trimester screening involving a simple blood test of several hormones and a non-invasive ultrasound, has become available. The combination of these tests detects about 75 percent of fetal problems. When they’re followed by second trimester testing, the detection rate is above 95 percent.

Though the American College of Obstetricians and Gynecologists now recommends first trimester screening for all pregnant women, many doctors still don’t offer it to their patients. Since it is fairly new, some may not know about it and others may not be trained to do the ultrasound, but some don’t offer it for ideological reasons—they don’t want the patient to consider terminating the pregnancy. A new study of over 38,000 pregnant women determined that all women should undergo first trimester testing, and when the results suggest a woman is at high risk, she should then be offered a minor surgical procedure involving a needle biopsy of the placenta (chorionic villus sampling or CVS) for confirmation or reassurance. This combination of universal screening followed by the CVS in those with a positive test is called contingent sequential testing. All of this should be completed before the twelfth week of pregnancy as it is in other Western countries like England.

The problem is, only 10% of people have easy access to CVS, so some drive to other cities to get it or others wait until they can do an amnio. I urge patients to ask their doctors about first semester screening—the more women who ask, the more doctors will be pressured into offering this important screening and as the demand for CVS increases, it will become more readily available as well.