Should pregnant women be offered genome screening for their unborn baby?

By Deborah Kotz, Globe Staff

With researchers announcing this week that they were able to sequence the genome of a fetus using only a blood sample from the mother, the potential for expanded genetic testing during pregnancy presents both new hopes and dilemmas for pregnant couples looking to find out as much as possible about their unborn babies.

The latest findings published on Wednesday in Nature add to an advance reported a month ago by other researchers who sequenced a fetus’s genome using blood from both the pregnant woman and the baby’s biological father.

While the experimental blood tests can provide an extremely reliable way to detect chromosomal disorders like Down Syndrome and Trisomy 18 within the first trimester of pregnancy, they could also identify metabolic conditions and immune system deficiencies that require treatment immediately after a baby is born.

Such a test could become available clinically within the next three years, said Stephen Quake, a bioengineering professor at Stanford University School of Medicine who led the Nature study.

But it also has the potential to pose serious ethical issues for parents who get a test result revealing, say, a gene that predisposes their unborn baby to early Alzheimer’s disease or premenopausal breast cancer -- but does not mean the baby would ever develop these illnesses.

“My concern is TMI, too much information,” said Dr. Diana Bianchi, a fetal medicine specialist at Tufts Medical Center. “How much of a snapshot should parents see about their baby’s future health?”

In a review paper published Friday in the journal Nature Medicine, Bianchi wrote that advances in fetal genetic testing will prove worthwhile if future treatments are developed to help the fetus in the womb. While researchers have largely abandoned genetic engineering to fix mutations in the womb, they’re focusing on developing treatments to reverse biological processes that result from some of these mutations.

Fetuses with Down syndrome, for example, tend to be under oxidative stress, a process that could damage their developing brains and lead to impaired learning and memory difficulties in childhood. Perhaps a treatment could be developed, said Bianchi, that expectant mothers of affected babies could take to lower their baby’s level of oxidative stress and help improve neural development.

Quake said he viewed his genome test as a “challenge” to other researchers to start working on treatments that could be administered in the womb.

(Both Quake and Bianchi have a financial interest in Verinata Health, which currently offers a genetic blood test for Down syndrome and trisomy 13 and 18.)

For the time being, couples appear to gain some benefit from learning about genetic problems earlier on in pregnancy, perhaps giving them more time to make a decision about whether to terminate or to prepare for raising a child with disabilities. Bianchi’s research found that women who knew they were carrying a fetus with Down syndrome had a more positive birth experience than those who learned the news after delivery.

And while older studies suggested that 90 percent of confirmed Down syndrome pregnancies were aborted, the latest research suggests that only 65 percent are. That could be due to the fact that screening for Down syndrome via blood tests and ultrasound imaging is now routinely offered to all pregnant women; in the past, it was offered only to those over age 35, and often those who opted for amniocentesis, which carries a small miscarriage risk, were those willing to abort if they found a chromosomal abnormality.

Beyond the nagging ethical concerns of doing a full genome screen, cost will certainly also be a factor. The genetic blood tests currently offered by Verinata and two other companies aren’t always covered by insurance and could cost patients between $200 to $500, according to Bianchi. “There’s a wide variation in coverage among managed care companies in Massachusetts,” she added, so some patients don’t have to pay anything while others have to pay the full amount.

A full genome test, if it comes into clinical practice, will likely be more expensive since in research settings the test costs about $3,000, said Quake.