Mira B. Irons, MD, is the chief of Clinical Genetics at Boston Children's Hospital. She sat down with Pediatric Views to talk about how Children's approaches prenatal testing, the services offered and the benefits of starting even before conception.
What kinds of prenatal testing are available at Children's?
We offer fetal imaging to look for growth or structural abnormalities. Three to 4 percent of babies are born with some form of major structural abnormality. We can perform an ultrasound—usually in the second trimester—that can identify if the fetus has a congenital heart defect, a cleft lip and palate or a kidney abnormality.
It's important to know if those structural abnormalities are there so we can help families make the right decision about where the child should be delivered. If a fetus has a congenital heart defect, you'd want the baby to be delivered near a hospital like Children's, as opposed to someplace where you might not have the necessary support. Our Advanced Fetal Care Center sees many of these patients, and some anomalies are amenable to fetal therapy or therapy right after delivery.
The ultrasound examination has evolved into fetal MRIs, which are done in specialized centers like ours, and can provide incredible detail regarding brain development.
Does Children's provide referrals for other kinds of genetic testing?
We can meet with couples ahead of time and go over their family histories, review records of other children who might have had problems, tell them what their risks are and discuss what kinds of prenatal testing we'd recommend.
Amniocentesis is traditionally a second trimester test to diagnose children with chromosomal abnormalities, inborn errors of metabolism or biochemical abnormalities, or even single-gene defects that can result in structural birth defects, growth or intellectual disability.
There's also a first trimester test called a chorionic villus sampling, where a small biopsy of the placenta is taken for specific genetic testing. This would be used to look for Tay Sachs disease, a non-treatable neurodegenerative disorder, or any other condition that can be diagnosed by looking for specific genes for abnormalities.
If we find that chorionic villus testing or amniocentesis is warranted, we can recommend couples to maternal fetal medicine specialists—many of whom work with genetic counselors who can take over during the pregnancy.
What are the risks for parents who are carriers?
A lot of couples think their level of risk is higher than it really is. Even parents who are at increased risk of having a child with a genetic or chromosomal abnormality are actually more likely to have unaffected children. A couple that's had one child with Down syndrome has about a 1 percent risk of having another child with Down syndrome— unless the mother is old enough that her age affects the risk, and even then it goes up to only 5 to 6 percent. If you have a couple who are both carriers for Tay Sachs, the risk of them having a child with Tay Sachs is roughly 25 percent. The reality is that three out of four of those babies will be fine, but there are some couples who are scared to even attempt a pregnancy because they don't know that. Quite often, prenatal testing actually provides reassuring information for them.
How early should parents consider prenatal testing?
The best place to start is before conception, if possible. There's no testing you can do preconceptually, but you can look at the family history to see if there are any red flags for increased risk of genetic conditions—structural abnormalities, intellectual disabilities, recurrent miscarriages or pregnancy loss, infertility. They may have a sibling with a genetic condition who hasn't been diagnosed. We can often make arrangements to have that sibling diagnosed to give them a better idea of what their risks might be. We also offer carrier testing prior to or early in a pregnancy.
The most important thing we can provide is real figures in terms of what a couple's increased risk is. If the fetus is identified as having a problem, couples need to decide how to move forward. We can provide the support they need to care for the fetus through the rest of the pregnancy and shortly after birth.
We look at the ways to optimize care for a child after delivery. If a fetus is identified with a chromosomal abnormality that's going to result in structural anomalies, intellectual disabilities or growth problems, parents can actually learn about them before birth and meet the doctors who are going to be involved in their child's care. That allows parents to focus on making the best decisions for themselves and their baby.