Prenatal Tests

	An ultrasound uses sound waves to "look" inside the uterus.

Ultrasound – Offered Between Weeks 16 and 20

An ultrasound directs high-frequency sound waves at the uterus. The 'echoes' produce an on-screen image. Ultrasound provides a general check of fetal anatomy and can help predict when your baby will be born.

Many parents welcome an ultrasound as a way to get a first look at this new member of their family. Depending on the position of the fetus, the ultrasound may show whether you will have a boy or girl. Ultrasound has been used for over 35 years and studies show it is safe.

An ultrasound may also be used at other times during your pregnancy to investigate and help diagnose issues of concern or simply to make sure that the baby is growing properly.

Screening Methods for Birth Defects

Two to three percent of babies are born with some form of birth defect. Down Syndrome accounts for half of these. The older the mother is, the higher the chance that her baby will have Down syndrome or a chromosomal abnormality.

You will likely be offered some additional tests to screen for birth defects, such as Down syndrome or neural tube defects like spina bifida. Different screening methods are used in different parts of Canada.

Maternal Serum Screening
Maternal serum screening (or MSS) is offered between 15 and 20 weeks. The MSS checks for a protein produced by the growing fetus called alpha-fetoprotein (AFP) as well as two hormones produced by the placenta. These substances cross the placenta into the mother's blood stream and can be detected with a simple blood test. The levels of these substances can help identify women at higher risk of having babies with chromosomal abnormalities like Down syndrome or neural tube defects like spina bifida.

MSS does not diagnose a chromosomal problem but estimates the risk of birth defects. Only two or three out of every 100 women who have an abnormal MSS will have a child with birth defects. An incorrectly estimated due date will make your hormone levels appear abnormal, producing a misleading MSS result. This is a common cause of false results.

Visit the Hospital for Sick Children's web site for more information about MSS.

Nuchal Translucency (NT) Test
A special assessment called a nuchal translucency (NT) test is done for some women who are at risk of having a baby with a chromosomal disorder, such as Down Syndrome. For example, women 35 years of age and older are at greater risk. The test is usually done between Weeks 10 and 14, to estimate the chance that the baby will have Down syndrome. The test consists of an ultrasound, which measures the amount of fluid at the back of the fetus’s neck. If the fetus has a chromosomal disorder, there is usually more fluid at the back of the neck. If the test shows an increased risk, followup tests, including an amniocentesis, can be done.

Integrated Prenatal Screening (IPS)
Integrated prenatal screening (IPS) is now offered as an alternative to MSS. The IPS combines information from an NT ultrasound with information from two blood tests – one done immediately after the ultrasound and one done between Weeks 15 and 20. Visit the Hospital for Sick Children's web site for more information about IPS.

Glucose Test – Suggested Between Weeks 24 and 28

Approximately three percent of pregnant women will develop gestational diabetes. Women with gestational diabetes rarely have symptoms; however, their blood glucose needs to be controlled to keep the fetus from getting too large and making the birth more difficult. Glucose control may involve dietary restrictions or medications like insulin.

The Canadian Medical Association recommends that all pregnant women be screened for gestational diabetes with a random glucose test. This is a simple blood test, usually done between Weeks 24 and 28. About 15 percent of women have high glucose levels on this screening test, but only a small percentage of these women will have gestational diabetes when further testing is done.

Group B Streptococci (GBS) Test – Suggested Between Weeks 35 and 37

A swab of your vagina and rectum is done to check for a common bacteria called Group B streptococci. Although the bacteria is harmless to you, it can cause meningitis or other serious infections in newborn babies. If the test is positive for GBS, you will be given antibiotics during labour to protect your baby.

HIV Test

When HIV is transmitted from a mother to her child, this usually occurs during delivery. If a woman knows she is HIV-positive early on, she and her doctor can take steps to reduce the chance of passing HIV on to her baby. These steps include the use of perinatal antiretroviral therapy, delivering the baby by cesarean section and avoiding breastfeeding. The Canadian Paediatric Society recommends that HIV testing be offered routinely to all women as early as possible during pregnancy and, in some cases, later in the pregnancy as well.

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