Down Syndrome Now Detectable In 1st Trimester
Thursday, November 10, 2005
A first-trimester screening test can reliably identify fetuses likely to be born with Down syndrome, providing expectant women with that information much earlier in a pregnancy than current testing allows, according to a major study being released today.
The eagerly awaited study of more than 38,000 U.S. women -- the largest ever conducted -- found that the screening method, which combines a blood test with an ultrasound exam, can pinpoint many fetuses with the common genetic disorder 11 weeks after conception. That allows women to decide sooner whether to undergo the riskier follow-up testing needed to confirm the diagnosis.
"This is a big deal for women. It's going to have a big impact on care for women, not just in the United States but throughout the world," said Fergal D. Malone of the Royal College of Surgeons in Dublin, who led the study published in today's issue of the New England Journal of Medicine.
Screening women before the second trimester allows those who might opt to terminate a pregnancy to make that decision when doctors say an abortion is safer and less traumatic. It also gives those who want to continue the pregnancy more time to prepare emotionally for their child's condition, and provides earlier reassurance to those whose babies are healthy, avoiding weeks of anxiety, Malone and others said.
"This is huge," said Catherine Y. Spong of the National Institute of Child Health and Human Development, which funded the $15 million eight-year study.
The American College of Obstetricians and Gynecologists, which issues influential recommendations for prenatal screening, will update its advice to reflect the findings, officials said.
Word of the study triggered criticism from opponents of abortion, however, as well as from those who object to its use to prevent the birth of children with Down syndrome.
Down syndrome is the most common major chromosomal abnormality, occurring in about 5,000 babies born each year in the United States. The syndrome results when a baby has three, rather than two, copies of the 21st chromosome, causing distinctive physical features, developmental problems and an increased risk of a variety of health problems that usually shorten the child's life span.
Currently, women, especially those at high risk because of their family history or age, are offered a blood test known as the quadruple test about 16 weeks into a pregnancy. Women who test positive can then undergo a procedure called amniocentesis to confirm the diagnosis.
The newer regimen uses an ultrasound test called the nuchal translucency to measure the thickness of the skin on the back of a fetus's neck and a blood test to measure levels of a protein called pregnancy-associated plasma protein A (PAPP-A) and a hormone known as human chorionic gonadotropin (HCG).
The study comparing the techniques involved 38,167 women at 15 U.S. centers who underwent both procedures and then were followed to see which fetuses had Down syndrome.
The first-trimester approach identified 87 percent of Down babies when used at 11 weeks, whereas the later quadruple test identified 81 percent. The two tests together picked up 95 percent of cases. Both produced false positives in about 5 percent of cases.
"In light of this study, we should offer screening to all women in their first trimester," Malone said.
Those whose results are most worrisome could then undergo a procedure called chorionic villus sampling (CVS) to confirm the diagnosis while still in the first trimester. Those whose results are less clear and are worried about the small risk of miscarriage posed by CVS can wait until the second trimester to undergo the quadruple test. If that is positive, they could then undergo amniocentesis, which also carries a small risk of miscarriage.
Women who would opt to terminate a pregnancy based on the results would be able to do so much earlier, when abortion is less risky and less traumatic, Malone said.
"By the time you're 20 weeks pregnant, most women will be feeling fetal movement. We wouldn't want to underestimate the psychological or emotional difficulty of undergoing pregnancy termination that late," Malone said. "Also, at that point it's easy to tell by looking at the woman if she is pregnant. This way she can make her decision in utmost privacy."
Women who test negative will be able to ease their minds much earlier.
"Thousands of women will be able to relax in the first trimester and not worry about this," Malone said.
But Gene Rudd of the Christian Medical & Dental Associations said he was concerned that women are not always fully advised about the risks of prenatal testing, and that screening could be used to try to eliminate babies with Down syndrome.
"What's the goal here? Is it to rid our society of Down babies? If that is the goal, I really have to question the civility of that," Rudd said. "The overwhelming number of people with Down will tell you their life is good."
Randall K. O'Bannon of the National Right to Life Committee said in an e-mail, "These tests appear to be used only to select babies for abortion, including as many as 5 percent who may not even have Down's Syndrome. . . . Killing a child with Down's Syndrome is not the solution to Down's Syndrome."
Malone and others, however, said they doubted the approach would result in more abortions.
"Most women are probably going to make the same decision now as before. If she decides to terminate the pregnancy, this just makes it safer and maximizes her privacy and confidentiality," Malone said.