Genetic Testing: Improving Prenatal Care Now and in the Future

by donald g. basel, md

genetic testing: improving prenatal care now and in the future

editorial submitted by Children's Hospital of Wisconsin

It’s been 19 years since scientists announced they had successfully sequenced the human genome. Since then, the field of genetics has exploded, with new technology and lower costs making genetic screening and testing a standard part of today’s health care.

This is particularly true in prenatal care. Obstetricians have long advocated that women have prenatal screening. Twenty-five years ago, ultrasound was the only screening tool.

Then came blood screening tests that measure levels of certain hormones and proteins in a mother’s blood. These tests can say whether a pregnancy has an increased chance of being affected by certain conditions, such as Down syndrome. Women who have abnormal results may choose to have followup diagnostic testing through chorionic villus sampling (CVS) or amniocentesis — both invasive procedures with some risk to the mother and fetus.

An improved screening option became available in 2011 with the release of the first commercial test capable of sequencing fragments of DNA from the placenta that are circulating in a pregnant woman’s

blood. Called non-invasive prenatal testing (NIPT), or cellfree testing, this test is now routinely offered to pregnant women. The DNA from the placenta usually is the same as the baby’s DNA, so analyzing it provides an opportunity for early detection of certain genetic abnormalities without harming the fetus. The test can be performed as early as nine weeks into the pregnancy up until delivery, with results available within seven to 10 days.

NIPT routinely screens for chromosomal disorders, including Down syndrome and trisomy 18. Screening for other chromosomal and genetic conditions is available, but the accuracy varies based on the condition. However, NIPT screening continues to improve as technology advances.

It’s important to remember that NIPT is not diagnostic. Abnormal results from NIPT screening may lead to CVS or amniocentesis to confirm a diagnosis. However, in the five to six years after the release of the original NIPT screenings, the frequency of amniocentesis or CVS has dropped dramatically in most academic centers.

analyzing DNA from the placenta provides opportunity for early detection of certain genetic abnormalities without harming the fetus

Also, because the test captures DNA from the placenta and the mother, it has the potential to reveal a genetic condition in the mother, something of which women and their obstetricians need to be aware.

The Role of Genetic Counseling When a woman undergoing NIPT has an abnormal screening result, it is important for her

to meet with a genetic counselor who can help her understand the medical information, as well as options for follow-up testing. When there is a diagnosis of a birth defect or genetic condition, a genetic counselor can also help a family understand what to expect and how to prepare for the birth of a child with special needs.

Another testing option routinely offered to expectant parents is carrier screening. This assesses the expectant parents’ risk of having a child affected with genetic conditions such as cystic fibrosis, spinal muscular atrophy and sickle cell disease. Low-cost carrier screening tests for these and other conditions are available today. Unfortunately, a lot of these tests are ordered with very limited counseling.

For couples considering carrier screening, it is also important to meet with a genetic counselor who can walk them through the decision-making process, help them decide what testing option

is best for their family and help them make sense of the results when they are complete.

Informed Decision-Making All prenatal genetic testing, whether carrier screening, NIPT screening or diagnostic testing from amniotic fluid or chorionic villi, is designed to help parents and their doctors make informed decisions about a pregnancy.

Some genetic disorders carry a more severe prognosis than others. Having this knowledge ahead of time can help a family understand what to expect at the time of delivery and prepare to care for a child with special needs.

From a doctor’s perspective, it helps us to know what to expect during the pregnancy and how to plan for the birth.

Genetic screening can also help identify conditions that are potentially treatable before birth, such as spina bifida.