40 is the new 35 when it comes high-risk pregnancy

It's one of the most serious decisions a pregnant woman makes: whether to have amniocentesis during her pregnancy to look for birth defects and chromosomal abnormalities such as Down syndrome.

The procedure, in which a small amount of amniotic fluid is extracted from the womb using a needle, carries with it a risk of miscarriage. Because the probability of abnormalities increases as women age, it has long been common practice for women older than 35 to undergo amniocentesis.

But a group of Canadian doctors and geneticists is challenging that approach. In an opinion paper published today in the Journal of Obstetrics and Gynaecology of Canada, the Society of Obstetricians and Gynaecologists of Canada recommends that maternal age should only factor into a decision about amniocentesis when a woman is over 40.

In other words, 40 is the new 35 when it comes to being labelled a high-risk pregnancy.

Today's opinion also strongly contradicts a paper published last year in the U.S. journal Obstetrics and Gynecology.

That paper which pegged the risk of miscarriage during amniocentesis at one in 1,600 pregnancies - much lower than the one in 300 figure that was previously widely accepted.

Those findings, the Canadian doctors wrote, are "misleading and should be interpreted with caution."

The doctors reviewed the one in 1,600 study. Known as the FASTER trial, the "First and Second Trimester Evaluation of Risk for Aneuploidy" compared 3,096 women who underwent amniocentesis with 31,907 women who did not.

Because the methodology did not include a number of pregnancies that were terminated because a chromosomal abnormality was found during amniocentesis, the Canadian doctors believe the rate of pregnancy loss in that group was underestimated. They think that some of those terminated pregnancies would have ended in miscarriage because of the abnormality, which would have raised the risk rate.

The doctors also reviewed more than a dozen other studies on the topic. They concluded that amniocentesis remains a risk, says Toronto geneticist Philip Wyatt, one of the SOGC committee members who worked on the paper.

This is the latest in a string of developments aimed at reducing the number of amniocenteses performed in Canada, especially within the demographic of women over 35, who until recently were routinely fast-tracked to the procedure.

It used to be that women crossed a wall after 35, immediately being considered high risk based on age alone. As Dr Wyatt puts it: "That wall's been moved to at least 40."

Doctors should be encouraged to collect as much information as they can with non-invasive testing, he adds, so the decision about whether to proceed to amniocentesis can be personalized to each pregnancy.

Twenty years ago, Dr. Wyatt says, age was all that doctors had to judge the genetic dangers of pregnancy and weigh the risks of amniocentesis. Now, there are eight or nine markers that can be detected through non-invasive tests.

The new guidelines, which were first published in February and repeated in today's opinion, will be a relief to women over 35 who were worried they would be slapped with a high-risk label.

Screening is now so good, it's not reasonable for all women from 35 to 40 to have amniocentesis, says Jill Davies, a genetics counsellor at the Medcan Clinic, a private health clinic in Toronto. "Even if you're over 40, your risk may be that of a 20-year-old. Screening is making you different from your age."

Dana Hollander's pregnancy was a textbook example of these guidelines in practice. Pregnant last year for the first time at 40, the Toronto professor was at no time labelled high risk for birth defects. After she had three non-invasive tests, including blood tests and a nuchal translucency test (an ultrasound scan that assesses the amount of fluid behind the neck of the fetus, an indicator for Down syndrome), she was told her risks were very low, so she decided against amniocentesis.

"My doctor repeatedly said I was not high risk," says the mother of Rosa, now six months old, "and that now is the time to step back and realize you can just have a normal pregnancy from here."

But Christina Honeywell, a genetics counsellor and educator at the Children's Hospital of Eastern Ontario in Ottawa, says stepping back from widespread amniocentesis would be a cultural, as well as a medical, shift. "It's such a long-held tradition, people have a hard time moving away from the idea that 35 is a magical age somehow."

Amniocentesis is still the only way to get a firm answer about any abnormalities, Dr. Wyatt says, so not everyone's comfortable forgoing it.

Tina, 40, is one of those women. She's in the midst of planning a wedding and trying to conceive. She says the new guidelines are a "slight comfort," but says even if she's at low risk, she's likely to go for an amniocentesis.

"Everyone I know who is past 35 has been having amnios. I would do it," says Tina, who requested anonymity. "I hate needles, but I'd do it."

source : www.theglobeandmail.com