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Midwifery Care – Screening for Birth Defects

Most healthy, low-risk women will have normal, healthy babies. Although rare, all babies are at some risk of developing chromosomal disorders. There is no such thing as zero risk. Deciding whether to test for these conditions is a personal decision and only you can choose what is best for you.

Screenings that test for birth defects include:

10–14 weeks first-trimester screening
This is a screening for Down syndrome, trisomy 13 or trisomy 18. This test involves blood work and an ultrasound. The blood tests measure the amount of two substances normally present in the mother’s bloodstream during pregnancy – PAPP-A (pregnancy-associated plasma protein A) and free beta-hCG (human chorionic gonadotropin, the “pregnancy hormone”. Abnormally high or low levels could signal a problem. The ultrasound is to measure the fluid behind the baby’s neck (nuchal translucency or NT). An increased NT may mean a higher chance for a chromosome problem.

Cystic fibrosis
This is an optional test to determine whether you are a carrier of the cystic fibrosis gene. Cystic fibrosis is a life-threatening disease that primarily affects the lungs and digestive system. Some people are carriers of the gene even though they do not have the disease.

MaterniT 21
This is blood test that can be performed as early as 10 weeks. It detects fetal chromosomal abnormalities such as trisomies 21, 18, and 13 to rarer abnormalities such as trisomies 16, 22 and other chromosomal disorders. This test is available for increased risk pregnancies with one or more of the following conditions:

  • Advanced maternal age
  • Personal history of chromosomal abnormalities
  • Fetal ultrasound abnormality suggestive of chromosomal abnormality
  • Positive serum screening test

15–20 weeks quad test
This test measures the levels of four substances in the mother’s blood, AFP (alpha fetoprotein), HCG (human chorionic gonadotropin), unconjugated estriol (an estrogen hormone) and dimeric inhibin A. These levels are then used to calculate the risk of chromosomal or neural tube abnormalities in your baby. If this test indicates a high probability, your care provider may recommend an amniocentesis.

16 weeks amniocentesis for genetic screening
This test is voluntary and may be recommended for certain high-risk patients or if one of the other screening tests returns an abnormal result.

Ultrasound at 18–22 weeks
This ultrasound is an ultrasound that examines the general appearance of the baby to assess for major abnormalities – brain, heart, spine, kidneys, stomach, legs, arms, chest, hands, feet, etc. And, of course, should you choose to find out, it will also tell you whether you are having a boy or girl. This test is also a screening test.