Genetic Testing During Pregnancy
Procedures, Ethical Issues, Pros and Cons

Testing For Genetic Problems While Pregnant

Genetic Testing During Pregnancy

Contents

• Introduction
• Why Was I Recommended Testing?
• Types of Tests
• To Test or Not to Test?
• Genetic Testing After 35

Back To Our Genetic Guide
For an overview, see:
Genetic Testing

Introduction

Many genetic abnormalities can be detected in a baby before birth, including:

• Down Syndrome
• Cystic Fibrosis
• Tay-Sachs disease
• Duchenne Muscular Dystrophy
• Hemophilia A
• Sickle Cell Anemia
• Polycystic Kidney Disease
• Thalassemia

Why Was I Recommended Testing?

Genetic testing before pregnancy helps high-risk couples make an informed decision about having children in the future. Genetic counselors are key to this process, as they can create a genetic profile based on the couple's family history. This profile, in addition to any recommended genetic tests, will calculate a couple's likelihood of having a healthy child. If there is a significant risk that a child will be born with a genetic condition or birth defects, and the couple still wishes to become pregnant, they may be recommended genetic testing during any pregnancy which occurs. If an abnormality is detected, the parents will then be faced with the decision whether or not to proceed with the pregnancy.

Genetic testing during pregnancy may also be recommended to:Women experiencing a pregnancy after 35, where the risk of Down syndrome is considerably higher. And, couples who already have children born with genetic abnormalities.

Types of Tests

There are different types of tests available. These range from non-invasive screening tests such as maternal blood tests and routine ultrasounds which can indicate a potential problem; to more invasive diagnostic tests which require removing a sample of cells around the woman's womb. Each procedure has its own advantages and disadvantages and a woman should consider all her options carefully.

Genetic screening is different to genetic testing. Genetic screening only tells a woman that there MAY be a problem with the fetus. Genetic testing is necessary in order to determine if there really IS a problem.

Screening Tests

Genetic screening of a fetus has advanced dramatically over the past number of years and continues to improve on a yearly basis. In fact many women are surprised by the speed of change, even from one pregnancy to the next. Genetic screening poses no risk to the baby and is used to establish which mothers require genetic tests. Genetic tests require a fetal tissue sample to be obtained and analyzed and carry a slight risk of miscarriage.

Ultrasound Scans
Routine pregnancy ultrasounds are one way a doctor checks for any abnormalities in a baby's development. Although scans are not 100 percent accurate, they do offer a first warning sign.

Triple/Quad Screen Test
Also known as the Multiple Marker Screening and AFP Plus. This test is important for assessing which women need further diagnostic investigation. Performed between weeks 15 and 20 of pregnancy, this test may be offered to mothers to screen for Down syndrome and spina bifida. Included in the screening is a test for human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), unconjugated estriol and sometimes inhibin A marker (which turns it from a triple to a quad test). This test is minimally invasive and only requires a blood sample from the mother. If for any reason the results are abnormal, the woman is referred to a genetic counselor to discuss prenatal diagnostic tests such as an amniocentesis.

Nuchal Translucency
This is another option for testing for Down syndrome; the primary benefit is that it can be carried out earlier than a triple screen test. A nuchal scan can be carried out between weeks 11 to 13 of pregnancy. It involves a maternal blood test, combined with an ultrasound scan. The scan measures the back of the baby's head (called the nuchal translucency). It requires considerable skill so there can be errors; the rate of false positives is in the 5 to 10 percent range.

Diagnostic Tests

If a potential issue is highlighted through the screening test, a diagnostic test is usually recommended. A sample of the placenta or amniotic fluid from inside the uterus is taken and sent to a lab to be cultured for a few days or weeks. This way the baby's chromosomes can be mapped. These tests are usually highly accurate in confirming the presence of genetic disorders, although they may not be able to determine the extent or severity of it. Diagnostic tests include:

Chorionic Villus sampling (CVS)
This prenatal diagnostic test can diagnose hundreds of disorders including Down syndrome, cystic fibrosis, sickle cell anemia and Klinefelter syndrome. A chorionic villus sampling (CVS) is performed in weeks 10 to 13 of pregnancy, and its main advantage is that it can be performed earlier than an amniocentesis test. During procedure, the doctor takes cells from the placenta and sends them to the lab for genetic testing. The earlier a diagnosis the better for many couples who might want to consider a therapeutic pregnancy termination. This test however is far less common than an amniocentesis.

Amniocentesis Test
Also known an amniotic fluid test or AFT, an amniocentesis test is usually performed between weeks 16-18 of pregnancy, but sometimes as early as weeks 13-14 or as late as week 23-24. The amniotic fluid which surrounds the fetus offers a range of genetic information about the baby. This test will help clarify any questions thrown up during a screening test and offer a more definite diagnosis if chromosomal abnormalities or fetal infections exist. This test is often used for diagnosing Down syndrome (trisomy 21), Turner syndrome (monosomy X), Edwards syndrome (trisomy 18) and Fragile X. It can also used for paternity testing, where parenthood is in dispute. The risk of miscarriage with an amniocentesis is 1-2 percent, which is lower than that associated with a CVS. This is primarily because an amniocentesis is carried out later in the pregnancy.

Cordocentesis
Sometimes called a Percutaneous Umbilical Cord Blood Sampling (PUBS), this test examines blood from the fetus to check for abnormalities. A thin needle is inserted through the womb, into the umbilical cord to retrieve a small amount of fetal blood. The sample is sent to a lab for analysis and results are usually returned within 2 days. The procedure is similar to an amniocentesis, except the objective here is take a sample of blood rather than amniotic fluid. This test can also check for Down syndrome, fetal anemia and fetal infections such as rubella or toxoplasmosis. The miscarriage risk is 1-2 percent.

To Test or Not to Test?

The reasons for testing will vary from couple to couple, but the following are a few of the benefits and disadvantages:

Why Some Couples Test

1. Medical interventions may be possible if a diagnosis is reached early enough.
2. Parents can begin to start planning for a child with special needs - both practically and emotionally.
3. A couple have the option to terminate the pregnancy rather than carrying the child to full term.

Why Others May Not

For others, even if they know they have a higher risk of having a baby with a genetic defect, they may still choose not to test. This may be because they would never consider a termination because of either personal ethical issues or religious reasons. Also, even though diagnostic tests have a very small chance of miscarriage, there is still a risk. Another issue is that knowing there are genetic problems is only half the story. The tests still cannot predict how severely the child will be affected. For example, finding a problem with a gene on chromosome number 7, which indicates cystic fibrosis, cannot predict if a child will develop serious lung problems or just mild respiratory symptoms.

Related Questions
What is cord blood banking?
How is cord blood collected?
How much does cord blood banking cost?

Genetic Testing After 35

The present standard of care in America is to offer an amniocentesis to all women who will be 35 or more at time of childbirth and delivery. The reason this age is picked is because the risk of having a baby with Down syndrome after this point is far greater than the risks of miscarriage resulting from an amniocentesis. If you are aged between 35 and 39 and have had a triple/quad screen test which indicates that your risk of Down syndrome is low, and your ultrasound scan was clear of problems, then it is reasonable not to have an amniocentesis. That is because the risks associated with an amniocentesis are then far greater than your risk of having a baby with Down syndrome. However, according to the American Institute of Ultrasound in Medicine (AIUM), all women aged 40 or over at time of delivery should have an amniocentesis, regardless of scan results.

Related Articles on Genetic Testing While Pregnant

For more on gene testing and related issues, see the following:

• Paternity Testing
• Ancestry Gene Tests and Sibling DNA Tests
• Grandparent DNA Testing and Y Chromosome DNA Test
• Twin DNA Testing

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