Pregnancy — or even planning a pregnancy — comes with a lot of questions.
You may have heard that the older you get, the higher your baby’s risk of Down syndrome. Maybe one of your relatives has sickle cell anemia or cystic fibrosis. How do you know how high your baby’s risk is? Are the screening tests you’ve read about worth it?
We sat down with prenatal genetic counselor Logan Karns, who frequently sees couples wrestling with these issues, and asked her some common questions.
What is prenatal genetic counseling?
Genetic counseling is a process of gathering information and evaluating the risk for a woman to have children with certain genetic conditions. I look at the couple’s family history and, if they are already pregnant, we discuss any screening tests they may have had.
If they are at a higher risk to have a child with a specific genetic condition, or if they have already had a screening test that indicates a birth defect, we talk about the next steps. This helps them to decide if they want to have more testing.
What are the chances of a significant birth defect in a low-risk pregnancy?
The background risk for any couple to have a child with a birth defect is 2-3 percent. The risk increases if the mother:
- Is over 35
- Has a family history of birth defects
- Had a previous child with a birth defect
Many birth defects happen by accident, with no known cause. When they do happen, most women wonder whether the birth defect happened because of something that they did. We try to reassure women that this is not the case.
What are the more common conditions you’re looking for?
- Spina bifada
- Cystic fibrosis
- Down syndrome
- Heart defects
- Sickle cell anemia
“Common” is, of course, a relative term, and everyone needs to look at a number and decide whether it feels like a high risk or a low risk to them.
When should a couple see a genetic counselor?
Usually I see couples in their first trimester. But it’s also not uncommon for me to see women in their second trimester, after they have received abnormal results from a screening test or procedure.
The best time for us to see people is before they are pregnant. We go through their family history, answer questions and talk about different approaches to screening based on either their family history or their ethnic background.
It is helpful to hear the information and make choices ahead of time. It can be more complicated when couples come in and they are already pregnant, and they have to make choices in a timely way. If we review the family history and identify something that requires testing, then timing can be a critical element.
What prenatal screenings and tests detect genetic conditions?
First trimester screening
Type of test: Blood test and ultrasound
When performed: Weeks 11-14
Recommended for: All pregnancies
Screens for: This test gives you your baby’s risk for certain chromosomal abnormalities, including Down syndrome. However, as it’s not a diagnostic test, you’d need more testing to determine if your baby has these conditions.
Non invasive prenatal screening (NIPS)
Type of test: Blood test
When performed: After 10 weeks
Recommended for: High-risk pregnancies, women over 35
Screens for: Specific chromosomal abnormalities. Like first trimester screening, this is a screening test and you’d need a diagnostic test to be completely sure.
Chorionic Villus Sampling (CVS)
Type of test: Placental cells collected either by using a catheter that goes through your cervix or by inserting a needle through your abdomen (similar to amniocentesis)
When performed: Weeks 11-13
Recommended for: High-risk pregnancies, women over 35
Screens for: Chromosomal abnormalities and genetic disorders
Amniocentesis
Type of test: Amniotic fluid cells collected through a needle inserted into the amniotic sac through your abdominal wall.
Timing: Weeks 15-22
Recommended for: High-risk pregnancies, women over 35
Screens for: Chromosomal abnormalities and genetic disorders.
QUAD Screening
Type of test: Blood test
Timing: Weeks 15 to 21
Recommended for: All pregnancies, offered to women who haven’t already had a screening test
Screens for: Down syndrome, trisomy 18 and spina bifada, but like FTS and NIPS, you’d need a diagnostic test if your results are abnormal.
A lot of these tests are recommended for women over 35. What’s so special about 35?
Because amniocentesis and CVS are considered invasive tests, there is a risk of complications, including miscarriage. The chance to have a miscarriage depends on which test you choose. At 35, the odds of having a baby with a chromosomal abnormality like Down syndrome or Trisomy 18 are about equal to the odds of having a complication from one of these diagnostic tests.
Why is NIPS only recommended in high-risk pregnancies?
The majority of studies involving NIPS have so far only looked at high-risk women. At this time, there is not enough information about the ability of the test to be helpful to low-risk women. The current recommendation from the American College of Obstetricians and Gynecologists is therefore not to offer NIPS to women considered low-risk. UVA has chosen to follow those recommendations. This may change as more published data become available.
I’m adopted and don’t know my family history. Should I still see a genetic counselor?
Genetic counseling isn’t just about going through your family history. We can still talk to you about your risk factors, including your ethnicity and the chances of a birth defect based on your age.
What happens if screening does reveal a significant birth defect?
When a birth defect is diagnosed during a pregnancy, support services are available to help parents decide how to manage their pregnancy. This is obviously a very painful and complicated time. We work with pregnant women and their families to outline all the options, help them choose how they would like to proceed and get them the support that they need.
Interested in meeting with a prenatal genetic counselor? You can:
- Ask your primary care doctor for a referral
- Contact our Maternal Fetal Medicine clinic at 434.924.2500.
