Women once had only one choice—to wait until their second trimester of pregnancy for prenatal screening for chromosomal abnormalities such as Down syndrome and trisomy 18. That is no longer the case. Newer tests allow expectant parents to determine a baby’s risk for these conditions as soon as the 11th week of pregnancy.

Even so, opinions on whether to test early are mixed. "There are pros and cons to either test," says Dr. Elias Sherman, chair of obstetrics and gynecology at Northwestern University's medical school.

Supporters of first-trimester screening say negative results reduce anxiety. The American College of Obstetricians and Gynecologists notes that if early screening is positive, parents can schedule more diagnostic tests sooner. They say it also gives a woman more privacy if she chooses to terminate the pregnancy.

But in a bulletin to its member physicians, the obstetricians’ organization maintains that precise timing and assessment of gestational age is essential for accurate results in the first-trimester screening. Second-trimester testing is still considered by most doctors to be the standard for care.

Experts say expectant parents considering first-trimester screening should be sure that appropriate ultrasound training and quality monitoring are in place at the facility, and that counseling and appropriate diagnostic testing are available if screening results are positive.

Heather Cunningham

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