Prenatal Screening

There have been many new developments in prenatal screening over the past few years. Traditionally, a child could be born with malformations or chromosomal abnormalities, causing great distress. The advent of obstetrical ultrasound helped us discover many kinds of abnormality, including those affecting the heart, kidneys or other organs. Detecting chromosomal abnormalities which affect the number or structure of chromosomes, however, was much more difficult.

Until very recently, amniocentesis was the only option open to mothers who were 35 or older when they gave birth. While pregnant women in this age group represent approximately 10 to 15% of all women who are pregnant, they also account for approximately 30 to 40% of fetuses with chromosomal abnormalities, the most frequent example being trisomy 21 or Down syndrome. The highest numbers of fetuses with chromosomal abnormalities are found in women under age 35. Amniocentesis is an invasive technique, abd carries some risk of causing a miscarriage.

New techniques for screening for chromosomal abnormalities have been developed over the past ten years. Screening is now more specific, reducing the number of amniocenteses performed and increasing the detection of such abnormalities. Nuchal translucency, 1st trimester serum markers, 2nd trimester serum markers and various combinations of all these tests represent the majority of screening tests now available. It should be understood that these tests are used for screening purposes, not diagnosis. If the results are abnormal, the next step would still be amniocentesis to know whether the fetus actually has a chromosomal abnormality or not.

Unfortunately, these screening tests are not readily available everywhere in Quebec and must be done on a private basis as they are not covered by the RAMQ. Talk to your obstetrician/gynecologist to learn about their availability and cost in your region and whether it would be appropriate for you to have such a test.

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