What can noninvasive fetal DNA testing tell us?

fetal dnaUntil relatively recently in human history, birth involved a lot of surprises. While a number of old wives’ tales promised a way to determine a baby’s sex and health status, the truth is that there was no accurate way of knowing these things until after the baby was born.

Today, of course, it’s a very different situation. Most mothers know (within a reasonable degree of accuracy) the sex of their baby months before it is due, and most of us go through the ancient ritual of counting baby’s fingers and toes on an ultrasound image 6 months into the pregnancy or even earlier. There are ways to detect (and even repair) certain kinds of fetal abnormalities long before birth, but many tests, especially invasive procedures, still pose a risk to the baby, mother, or both.

Amniocentesis is one such test. It can detect several kinds of genetic anomalies, such as Down syndrome and several others. It can’t be performed at all until the 15th week of pregnancy or later, and because it is invasive, performing it could injure an otherwise healthy fetus.

This is why the noninvasive prenatal genetic testing options available now are so exciting. Prenatal genetic testing for Down syndrome and other abnormalities now exist that don’t require amniotic fluid collection and pose minimal to no risk to the pregnancy.

Because they are so closely linked, there are small amounts of the fetus’ DNA present in the mother’s blood and other fluids. Non-invasive prenatal genetic testing (also called cfDNA testing) can detect and analyze this fetal DNA using either a blood or urine sample form the mother, and does not involve the fetus directly at all.

These cfDNA tests can detect genetic abnormalities like Down syndrome, Edwards’s syndrome, fragile X syndrome, and Turner syndrome. They can tell the sex of the baby as well, if it has not already been determined by an ultrasound. Other similar tests can detect signs of Tay-Sachs disease, muscular dystrophy, cystic fibrosis and even sickle-cell anemia (learn more here).

Of course, no test is “perfect.” Most cfDNA tests are not absolutely conclusive that a fetus will have a condition, but rather whether the child has a higher than usual chance of being born with one of these conditions. If the baby is at risk, parents and doctor can discuss whether more certain but more invasive tests should be carried out. What these cfDNA tests are best for is letting the vast majority of soon-to-be parents know whether their child may have any of the genetic problems the tests could detect, without putting the baby at any risk just due to the test.

Essentially, they let you set your mind at ease if (as in most cases) nothing is detected, and help you decide if more invasive testing should be done to be more informed and better prepared for pregnancy and parenting.