Knowing the Risks: Prenatal Testing and You
Pregnancy can be an anxious time for women, especially those who may be at higher risk for certain complications.
UR Medicine offers prenatal testing for expecting mothers at the Biochemical Genetics Laboratory at Strong Memorial Hospital.
Together with Department of Obstetrics and Gynecology, this team of clinical professionals helps provide families with answers to crucial questions before a baby is born.
How it Works
In New York State, all pregnant women in their first trimester are offered an optional blood test to screen for certain fetal defects. The patient’s OBGYN can order the test and have her sample sent to the laboratory.
From there, a team of medical technologists process the sample on an automated lab instrument that issues a report with the odds of certain complications. These results go to the ordering physician within 24 hours.
The first trimester maternal serum screening test assesses the risk for chromosomal defects – Down syndrome and Trisomy 18 – by combining the blood test result with a specific ultrasound measurement. Expecting mothers can later have a second trimester AFP only screening for spina bifida.
If the first screen comes back negative, no further testing is required. If the result is positive, patients are directed to a prenatal counselor who meets with them to take a more in-depth look.
The risk level depends on a number of factors including age, ethnicity and family history. While the first trimester screening provides an assessment of the risk, it is still too early to determine a diagnosis.
Jeanne Peterson is a reproductive genetics counselor at URMC who has spent more than 30 years consulting families facing possible or likely issues during pregnancy.
The vast majority of positive screens in the first trimester are actually false positives, she explains. Still, parents are often alarmed when they hear there is a higher-than-average risk of something going wrong.
“Once the patient gets that phone call from their doctor that they weren’t expecting, this cloud comes over them,” said Peterson. “Many times they’re not getting all the information about the results, and even the information they’re getting they might not understand very well.”
For example, an expecting mother with a 1 in 200 chance (0.5 percent) of having a baby with a birth defect is at much lower risk than someone with a 1 in 6 chance. By learning about their test results and what the numbers mean, many walk out the door feeling reassured and prepared for next steps, whatever they may be.
“You have to help people through it,” said Peterson. “You have to empower them by giving them information at the level they can understand.”
Higher risk individuals with a positive first screen can decide whether to have optional follow up testing for chromosomal abnormalities.
Advances in the last decade have provided a less invasive option than the traditional procedures, explains Dr. Robert Mooney, director of the Biochemical Genetics Laboratory at URMC.
Patients used to be limited to amniocentesis – a test that samples the amniotic fluid around the fetus – or CVS – which requires a small sample of the placenta early in pregnancy – to get a definitive diagnosis. Today, there is a less invasive option that often eliminates the need for more invasive procedures.
Robert Mooney, Ph.D.
The cell-free fetal DNA blood test is available for mothers as early as 10 weeks of gestation. This test analyzes genetic material from the placenta that is present in a woman's blood during pregnancy. It can accurately eliminate most false positives and identify those pregnancies with a high risk of an abnormality.
“This has really taken over as the next step after we identify a screen positive,” said Dr. Mooney. “In most cases this eliminates the false positives and identifies those who are at very high risk. We’ve now narrowed the population down to a few at very high risk rather than 3 to 5 percent who have screened positive by our (first trimester) blood test.”
Patients who still test positive after the cell-free DNA test can then choose to have amniocentesis or CVS to obtain a definitive diagnosis.
A Team Effort
The prenatal screening program at URMC is a combined effort of the Department of Obstetrics and Gynecology and the Biochemical Genetics Laboratory. Representatives from both areas meet regularly to review individual cases, changes to testing, or population trends.
“We’re part of a team,” said Dr. Mooney. “Prenatal Screening is successful only because we all work together. We communicate (with OBGYN) constantly and they give us information to help us interpret the results appropriately.”
The lab considers each test to represent a person and a family waiting anxiously for answers. The team operates on the presumption that every single result is important, says lab supervisor, Matthew Morriss.
“Each sample is unique,” he said. “It has a person at the end of it and we treat each one with the same urgency. These results are important and we want the doctor and the patient to have all the information that we can give them.”
As a counselor, Peterson says she finds it rewarding to help expecting parents be better prepared for the next step of their journey.
“I tell them that most babies born to all couples are healthy and normal and most likely this baby is healthy and normal, too,” said Peterson. “These screening tests sometimes create bumps in the road but the majority of the times, things turn out okay.”
Bethany Bushen |