Prevention; Your Pregnancy Matters

Planning for pregnancy? Peek into your genetic compatibility with carrier screening

Prevention; Your Pregnancy Matters

Carrier screening can help people considering having children understand whether they carry genetic variants for more than 500 hereditary genetic disorders.

Co-parenting involves a lot of give and take. From discipline styles to diaper duty, couples that are more compatible may find the journey of parenthood a bit less rocky. While there’s no DNA test to see whether you’ll argue over doing the dishes (hint: you will), genetic carrier screening can provide insight into your future baby’s health.

Carrier screening estimates the chances a child you have with your partner might inherit a genetic condition, such as sickle cell disease, cystic fibrosis, or spinal muscular atrophy (SMA).

If you carry a variant in one of the genes that is screened for, it may not affect your health but there is a possibility it could be passed to your baby. In general:

  • If one parent is a carrier, there is a 50% chance the child would also be a carrier.
  • If both parents are carriers, there is a 25% chance the child would be born with the condition and a 50% chance they’d be a carrier.
  • If only the mother is a carrier for an X-chromosome-linked condition such as fragile X syndrome or Duchenne muscular dystrophy, there is a 50% chance that a son would be born with the condition and a 50% chance that a daughter would be a carrier.

Getting prenatal carrier screening can provide peace of mind and additional information to help you plan for your pregnancy and child. If you choose to be screened, our preconception and prenatal genetic counselors are available to meet with you to review your family history, discuss carrier screening options, and explain the logistics for getting tested. They will also explain your results and provide options for further testing or medical care if needed. You can also discuss carrier screening with your gynecologist at an annual visit or with your obstetrician if you are pregnant.

Carrier screening is routinely offered at UT Southwestern when you establish prenatal care with one of our providers.

How does carrier screening work?

Whereas genetic screening commonly ordered during pregnancy is focused on detecting fetal chromosome abnormalities that occur by chance such as Down syndrome, carrier screening examines the parents’ DNA only for potentially hereditary recessive or X-linked gene variants. Recessive means that both parents would have to be carriers for there to be a chance that their child could be born with an inherited genetic condition. X-linked means that the condition is caused by a gene on the X chromosome, so a female carrier has a chance to have a son with an inherited genetic condition.

The screening itself is easy and can be done in our office or from the comfort of home. You’ll spit into a tube using a mail-in kit or get a simple blood draw in the clinic. The sample is sent to a secure lab, and it takes two to three weeks to receive the results. We will discuss your results with you directly to make sure your questions are answered, and your results will appear in your UTSW MyChart account.

Carrier screening can be done either while you are planning a pregnancy or are already pregnant. It does not need to be done more than once in your life. Carrier screening is very accurate, however occasionally the results are not straightforward. Some carrier screening results indicate that an individual has a chance to be a carrier but are not definitive.

A negative result on carrier screening means that your chance to be a carrier of the conditions that were tested is very low but cannot be eliminated. No carrier screening checks for all possible genetic conditions.

So, if you have questions about your carrier screening results, it’s important to ask your doctor or discuss your results with a genetic counselor to keep them in perspective. The screening should not be taken as a directive of whether to become pregnant with your partner.

Who should consider carrier screening?

Carrier screening is optional. Any adult can be tested to see if they are a carrier for genetic conditions as family history may not indicate whether someone is a carrier. The American College of Obstetricians and Gynecologist recommends that all women be offered carrier screening for cystic fibrosis, sickle cell disease, and spinal muscular atrophy (SMA).

We used to be able to screen for only a handful of disorders that were most common among individuals of specific races and ethnicities. Over time, we have recognized that all individuals can be carriers for genetic conditions and genetic screening technology has improved tremendously. Now we can screen for as many as 500 genetic conditions for couples who are interested in that information.

Routine carrier screening tests often check for the most common conditions that an individual of any ethnicity could be a carrier for, including between 4 and 27 conditions. If you have completed carrier screening in the past through your doctor, you can check your test report or check with your doctor’s office to find out how many conditions for which you were screened.

Many health insurers cover carrier screening, and we can provide more information regarding the cost of testing and billing options when carrier screening is ordered.

Related reading: How to manage anxiety about pain during common pregnancy tests

What happens if I am a carrier?

It is not unusual to be identified as a carrier for a genetic condition, particularly if you had a carrier screening panel that included a larger number of genes. Most carriers for recessive or X-linked genetic conditions have zero symptoms and being a carrier does not change your health or medical management. And remember, most carriers for genetic conditions have no family history of the disorder. When one person is found to be a carrier for a recessive condition, the next step is often to perform carrier screening for the partner.

Even when both partners are carriers for the same recessive condition, it doesn’t mean that your baby will be born with the condition. In fact, for most conditions, there is a 75% chance the baby will be born healthy when both parents are carriers.

If you or your partner are carriers of a genetic condition, the counselor will talk you through the results of the test and the chances of having a child with a specific disorder.

Patients who are not pregnant yet may choose to:

  • Get pregnant as planned and consider testing during the pregnancy or after the baby is born.
  • Use a donor egg or sperm to conceive.
  • Use in vitro fertilization to test the embryos before they are transferred.
  • Consider adoption.

Patients who are already pregnant may choose to test the baby for a genetic condition after delivery or consider prenatal genetic testing to diagnose the condition before birth. We offer two prenatal diagnostic tests at UT Southwestern. Both are performed by our maternal-fetal medicine physicians, who specialize in caring for high-risk pregnancies and performing procedures during pregnancy:

  • Amniocentesis, which can be performed any time after 16 weeks gestation. We begin with an ultrasound of the uterus to locate the placenta, fetus, and the surrounding amniotic fluid. A pocket of fluid is identified on the ultrasound. A thin needle is then inserted through the abdomen into the uterus to withdraw some amniotic fluid from that pocket.
  • Chorionic villus sampling (CVS) is typically performed between 11-13 weeks gestation. We begin with an ultrasound of the uterus to locate the placenta and fetus. CVS involves collecting a tissue sample from the placenta, or a placental biopsy. There are two ways of obtaining the placental sample, depending on where the placenta is located inside the uterus.

Both prenatal diagnostic tests are associated with a very small risk for complications or miscarriage. The risk is less than 1%, or in between 1 in 500 to 1 in 1,000. We take precautions with every prenatal diagnostic procedure to avoid complications.

Genetic compatibility can influence how you decide to grow your family. Often, we can give patients peace of mind and options to consider with pregnancy planning. While we can’t guarantee you’ll always agree on the nitty gritty of parenting, your Ob/Gyn and prenatal genetic counselor can provide additional information to help you make the best health decisions for your family and pregnancy.

To discuss carrier screening before or during pregnancy, call 214-645-8300 or request an appointment online.