Prenatal and diagnostic testing: What to know before you test

Weighing risk vs. ‘yes or no’ answers

“Risk assessment is a difficult concept for many patients,” Dr. Wick says. “We all have a different perception of what is considered ‘high risk,’ and we all want a definitive yes-or-no answer, not a risk!

“Some patients consider 1/200 (a positive test result based on a cutoff of 1/230) to be unacceptably high, and will proceed with testing. I have also had patients with a much higher risk, 1/25, decide that this is not high enough to proceed with additional testing,” Dr. Wick continues.

“The decision to proceed or not may be based on how the patient/couple will manage the pregnancy,” Dr. Wick says. “If termination is a consideration, these couples will usually proceed with invasive testing so that further management decisions can be made.

“If couples are not considering termination, then it may be reasonable to weigh the risks of the procedure versus the risk that the pregnancy is affected.”

Plan of delivery

Every delivery is different, and each couple must approach delivery with a plan that works for them.

“If the fetus has a lethal condition, it may also be useful to meet with the neonatologist to discuss management at delivery,” Dr. Wick advises. Depending on the baby’s condition, a couple may choose “comfort care” versus multiple interventions.

“You should also discuss plan of delivery with your provider,” Dr. Wick says. “These are obviously very sensitive issues.”

Hearing the results

At the beginning of our pregnancy, my husband and I agreed it didn’t matter what might be different about our child, we looked forward to meeting him or her and starting our family.

When the first screening results came back, the numbers were like an unexpected flare shooting into the sky. We talked at great length about the pros and cons of going further and having diagnostic testing. It was riskier to the baby because diagnostic tests are invasive, whereas the screening I’d undergone to that point was from simple blood tests.

Together, we agreed we wanted to know what was reasonable to find out. We wanted to be prepared, and, as we learned more about Trisomy 18 and Trisomy 21, we realized either scenario came with increased risks of heart defects. We decided we had to know more.

Diagnostic testing

At 18 weeks, I underwent an amniocentesis, a diagnostic test that’s often used to follow up on an abnormal screening test. Diagnostic tests can better confirm genetic conditions.

Dr. Wick explains, “Diagnostic testing is also referred to as invasive testing. This includes chorionic villus sampling (CVS) and amniocentesis (amnio).

“CVS is typically performed between 11 and 14 weeks. It involves taking a small sample of the placenta (chorionic villi). This may be done with a needle through the abdomen (transabdominal; similar to amnio) or by passing a small catheter through the cervix (transcervical). CVS is done under ultrasound guidance. The quoted risk of pregnancy loss is approximately 1 percent.

“Amniocentesis typically is done at or after 15 weeks and is also usually done under ultrasound guidance,” Dr. Wick continues. “Risk of loss is generally quoted as 0.5 percent. Both CVS and amnio obtain fetal tissue, which can be used for chromosome analysis or other genetic testing.”

For us, prenatal testing also helped discover and track our son’s evolving hydrops condition. Hydrops is two or more of the following 1) ascites [fluid collection in the abdomen], 2) pleural effusion [fluid around the lungs] 3) pericardial effusion [fluid around the heart], 4) skin edema [e.g., fluid collection in the extremities, similar to what many women experience late pregnancy but usually more pronounced], 5) polyhydramnios [abnormally increased amniotic fluid].

“Hydrops can be associated with several conditions, including Down syndrome,” Dr. Wick explains, “but it generally carries a poor prognosis.”