Specialist Advice — 5 minutes

Prenatal and preimplantation diagnosis

Raymond Lepage, PhD, Doctor in Biochemistry
Raymond Lepage, PhD, Doctor in Biochemistry
Science popularizer

A prenatal diagnosis (PND) identifies fetal abnormalities or genetic diseases during pregnancy. In the context of a disease already identified in your family, before doing this test, we need to identify whether you have the mutation or, in the case of a recessive transmission disease, whether this mutation is present in both parents. Depending on the disease, even if the mutation is known, the PND can determine whether or not the fetus is affected, but it is not possible to predict the severity of the symptoms.

You can choose one of two procedures for a prenatal diagnosis:

Chorionic villus sampling (placenta biopsy)

  • Done using the DNA extracted from this sample.
  • Undertaken between the 10th and 12th week of pregnancy.
  • An associated risk of fetal loss (miscarriage) of about 1% (1 in 100).
  • An approximately 2% risk of the sample being contaminated with cells of maternal origin. In such cases, the test would not be reliable and an amniocentesis would be required to establish a diagnosis.
  • The accuracy of this prenatal test is assessed at 98%.
  • Results are available 2-3 weeks after the procedure.

Amniocentesis

  • Consists of an amniotic fluid sample.
  • Done using the DNA extracted from this sample.
  • Usually undertaken after the 15th week of pregnancy.
  • An associated risk of fetal loss (miscarriage) between 0.25% (1 in 400) and 0.5% (1 in 200).
  • The accuracy of the test is 99.8%.
  • Results are available 2-3 weeks after the procedure.

As for the Preimplantation Diagnosis (PID), it can detect the presence of potential genetic or chromosomal abnormalities in embryos conceived after in vitro fertilization. In this case, a genetic test is done on a few cells taken from each embryo. Embryos carrying the mutation can therefore be excluded and only unaffected embryos are implanted in the uterus.

The disadvantages of the PID include the associated costs, the ovarian stimulation process, in vitro fertilization, the possibility that few (or no) embryos will be available for transfer and the implantation rate of approximately 30-35%.

For professional support, we’re here for you.

We offer services and ressources that can help your doctor support you during your pregnancy.

  • Urine pregnancy test: A pregnancy test involves measuring the level of beta-hCG, the hormone produced by the placenta in a pregnant woman.
  • Beta-hCG: hCG (human chorionic gonadotropin) is the pregnancy hormone. This test measures a very specific part of hCG in the blood, namely its beta subunit. The beta-hCG test is used to diagnose and monitor pregnancies, placental diseases and germinal tumours.
  • Prenatal screening test: Performed during the first trimester of pregnancy, the PreNatest (prenatal screening test) uses a drop of blood to evaluate the risk of carrying a fetus affected by one of the most common birth defects: trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome).
  • Guide on prenatal screening: this clear and comprehensive guide helps you better understand fetal DNA screening for trisomies and supports your discussion with your doctor.
  • First-trimester ultrasound: Provides a more accurate determination of the gestational age of the fetus. The ultrasound is performed between the seventh and ninth weeks of pregnancy.
  • Nuchal translucency: Provides important medical information such as fetal size, age and health status. It can also detect the presence of twins and diagnose certain birth defects.
  • Other first trimester testing.

Do you have a medical prescription for one of these tests? Book an appointment online or contact Biron Health Group’s customer service at 1 833 590-2712.

Raymond Lepage, PhD, Doctor in Biochemistry
Raymond Lepage, PhD, Doctor in Biochemistry
Science popularizer
For about 50 years, Raymond Lepage worked as a clinical biochemist in charge of public and private laboratories. An associate clinical professor at the Faculty of Medicine of the Université de Montréal and an associate professor at the Université de Sherbrooke, he has also been a consultant, researcher, legal expert and conference speaker. He has authored or co-authored more than 100 publications for scientific conferences and journals, and now devotes part of his semi-retirement to popularizing science.