Pregnant Women 

The Medical Genetics program at BC Women's Hospital & Health Centre sees couples for genetic counselling if they have an ultrasound abnormality, an abnormal maternal serum screen, or a family history of a genetic condition.

Below is some information about our program and prenatal screening and diagnosis:

• Prenatal Referrals
• Medical Genetics Referral
• What to expect at the appointment 
• Prenatal Screening
• Maternal serum screening
• Ultrasound screening
• Prenatal Diagnosis
• Ultrasound
• CVS
• Amniocentesis  
• Fetal Diagnosis Service (FDS)
  

Prenatal Referrals

Whenever possible, families should be referred to Medical Genetics before initiating a pregnancy. If this is not possible, it is important to have a referral early in a pregnancy so appropriate arrangements for testing can be made.

Pregnant women may be referred for assessment, counselling, and/or prenatal diagnosis in circumstances such as the following:

• Positive maternal serum screening: Pregnant women identified by prenatal serum screening as being at increased risk for a chromosomal abnormality or neural tube defect. 
• Women in which an ultrasound has shown a potential concern in their current pregnancy.
• Couples in which either person has had:
• another child or stillbirth with a chromosome abnormality;
• another child with a neural tube defect such as spina bifida or anencephaly, or a close relative (brother, sister, niece, nephew) with a neural tube defect;
• another child with a known or suspected genetic disorder, birth defect, or developmental delay.
• Couples in which either person is known to have a chromosome rearrangement.
• Couples in which one or both partners have a known or suspected genetic condition or birth defect.
• Couples in which both partners are carriers of a recessive genetic disorder, for example:
• Thalassaemia (more common in Mediterranean, Asian and East Indian populations)
• Tay Sachs (more common in the Ashkenazi Jewish population)
• Sickle cell anemia (more common in the African, Spanish, Mediterranean, Middle Eastern and Indian populations)
• Cystic fibrosis (more common in the Caucasian population)
• Family history of known or suspected genetic disorders, for example: Duchenne Muscular Dystrophy, Hemophilia, Myotonic Dystrophy, or Fragile X Syndrome.
• Women who have been exposed during pregnancy to certain drugs or other chemicals that may cause birth defects. If you have a concern about an exposure, you should first have your physician contact us to see if your exposure puts you at an increased risk.

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How do I get referred to Medical Genetics?

Have your physician complete the appropriate form located on the Contact Us/Making a Referral page.

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What to expect at the appointment

Many couples are referred to Genetic Counselling because they have an ultrasound abnormality, an abnormal maternal serum screen, or a family history of a genetic condition. A genetic counsellor will review the case, including relevant family and pregnancy histories, and evaluate whether further testing would be indicated.

Prior to meeting with a genetic counsellor, you may be scheduled to have an ultrasound at Greig Associates or BC Women’s Hospital. This will be scheduled 1.5 to 2 hours ahead of the appointment in Medical Genetics, and may be booked at either BC Women’s Hospital or Greig Associates.

If you are offered an amniocentesis for prenatal diagnosis during your appointment, your genetic counsellor can book this following your appointment. If you are traveling from out of town, we will ensure there is a spot available to you on the same day.

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Prenatal screening

Pregnancy should be a healthy and happy time. Many women worry about their pregnancies, but most give birth to normal healthy babies.

Prenatal screening tests are used to identify women who may be at an increased risk to have a baby with a particular birth defect or condition. They cannot diagnose a specific condition. The primary purpose of prenatal screening is to identify at-risk individuals from a larger population and offer them further testing, information and options.

Maternal serum screening is available to all pregnant women, regardless of age. It is an optional test and women should be counselled about the possible outcomes prior to testing.

There are different maternal serum screen options depending on maternal age and the gestational age at which a woman presents. All of these screening tests estimate a woman’s chance of having a baby with the following three conditions:

• Down Syndrome
• Open spina bifida
• Trisomy 18

For details on these tests, please see the Prenatal Screening Program  (http://www.bcprenatalscreening.ca)

If maternal serum screen results indicate an increased risk for one of the three above-mentioned conditions, diagnostic testing by amniocentesis will be available.

Ultrasound is also used for prenatal screening. A detailed ultrasound performed between 16-20 weeks of pregnancy can screen for chromosome abnormalities by assessing soft markers. These findings are often considered ‘normal variants’, however they also increase the risk for chromosome abnormalities.

Some soft markers on ultrasounds that are commonly reported include: 

• Choroid Plexus cysts (CPCs) : Small cyst(s) found in the choroid plexus (an area of the brain that produces fluid). When seen alone, there is a small increased risk for Trisomy 18. There is no association with abnormal brain development. 
• Echogenic intracardiac focus: A bright spot in the fetal heart. When seen alone, it is associated with an increased risk for Down syndrome. It has not been associated with congenital heart disease.
• Pyelectasis: An enlarged space in the fetal kidney measuring 5-10mm. When seen alone, it does not significantly increase the risk for Down syndrome. An ultrasound of the baby’s kidneys should be performed after birth. If the measurement is >10mm, referral to Medical Genetics is recommended.
• Nuchal thickening: Increased thickness of the skin at the back of the fetal neck. Associated with an increased risk for Down syndrome. 
• Short femur: A short femur length (thigh bone) in relation to the size of the fetus. Increases the risk for Down syndrome.
• Echogenic bowel: A bright spot in the fetal bowel (intestine). Associated with an increase in the risk for aneuploidy. Also associated with an increased risk for fetal infection, cystic fibrosis and obstetrical complications. Further testing is recommended.
• Single Umbilical Artery: The absence of one of the arteries in the umbilical cord. The risk of aneuploidy is not significantly increased. It has been associated with reduced fetal growth, and therefore a third-trimester ultrasound is recommended.

As with maternal serum screening, soft markers are NOT diagnostic. They are NOT structural abnormalities in the fetus.

The overall risk will be evaluated based on ultrasound findings and maternal age, and maternal serum screening results if performed. Amniocentesis will be offered if the risk for a chromosome abnormality is greater than the risk of miscarriage associated with the procedure (1/200).

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Prenatal Diagnosis

There are a number of reasons for offering women prenatal diagnosis, such as having a positive maternal serum screen result, an ultrasound finding, a previous pregnancy with a chromosome abnormality or a family history of a genetic condition. Doctors use information about the woman’s age as well as the couple’s health and family history to determine if there is a need for special testing before the baby is born.

If there are concerns about your pregnancy, the decision about having a procedure for prenatal diagnosis will be up to you. You should only make this decision after talking about your health and family medical history with your doctor. The choice about prenatal diagnosis is made by a couple based on their risks, values, and beliefs.

There are different tests available for prenatal diagnosis:

• Ultrasound
• Amniocentesis
• Chorionic villus sampling (CVS)

Ultrasound is able to diagnose certain differences in how a fetus has developed structurally. A detailed ultrasound performed in the second trimester assesses the growth and anatomy of the fetus. It can evaluate the structure of the heart and other internal organs, brain, spinal cord, as well as the face and limbs. Ultrasound is NOT able to detect all differences in how a fetus has developed.

Amniocentesis is performed after 15 weeks gestation. It involves removing a small amount of amniotic fluid from the uterus in order to analyze the fetal chromosomes or DNA. This is done by inserting a needle through a woman’s stomach and into the amniotic sac (uterus). There is a 1/200 (0.5%) risk of miscarriage associated with this procedure.

Chorionic villus sampling (CVS) is performed between 10-13 weeks gestation. The CVS samples cells that form the placenta in order to analyze the fetal chromosomes or DNA. This is done by inserting a needle through a woman’s stomach or cervix to reach the placenta. There is a 1/100 (1%) risk of miscarriage associated with this procedure.

Unlike amniocentesis, the CVS does not assess the risk for open spina bifida; this can be done through measuring AFP in maternal serum during the second trimester.

All couples with every pregnancy have a 5% risk of having a child with a serious congenital anomaly or handicapping condition, recognized by one year of age. These diagnostic tests can find some, but not all, birth defects before the baby is born.

For more details, see Prenatal Diagnosis and Treatment

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Revised: July 9, 2009