Newborn Screening and Prenatal Diagnosis

Prenatal tests and newborn screening can help to facilitate an early diagnosis of cystic fibrosis (CF), caused by mutations in the gene CFTR.

While there is no cure for CF, there are treatments available that can ease symptoms for those born with the progressive disease. Quality of life is significantly better when care is started early, so getting a diagnosis is very important.

Everyone inherits two copies of the CFTR gene, one from each biological parent. CF is recessive, which means the disease only develops if both copies of the gene are mutated. If just one copy of CFTR is altered, the person will not develop CF, but may pass the disease-causing mutation to any future biological children. Thus, individuals with one altered CFTR gene are said to be “carriers” of the disease.

What is prenatal testing?

A prenatal diagnostic test is used to identify, before birth, whether a baby is carrying CFTR mutations that will cause CF. The test results have a high degree of certainty about whether or not the fetus will develop CF, but cannot predict disease severity.

Prenatal testing essentially involves taking a small sample of tissue from the developing fetus, then sending it to a lab to test it for disease-causing mutations. To collect the fetal tissue sample, two approaches are commonly used: chorionic villus sampling and amniocentesis.

Chorionic villus sampling (CVS) is usually done between 10 and 13 weeks of pregnancy; it involves removing a small piece of tissue from the placenta to check for genetic mutations. The placenta grows along with the fetus during development, helping to supply the fetus with nutrients and remove waste products.

CVS can either be performed by inserting a needle through the belly into the womb (transabdominal), or by passing a small tube through the vagina and past the cervix (transcervical). In both cases, the collection is guided by an ultrasound.

Amniocentesis, sometimes abbreviated as “amnio,” is typically performed at 15 to 20 weeks of pregnancy. It involves taking a sample of the amniotic fluid — the fluid that surrounds the developing fetus in the womb — and testing fetal cells in the fluid for disease-causing mutations. The fluid is usually collected with an ultrasound-guided needle inserted through the belly and into the uterus.

Notably, both of these tests are relatively invasive, and they may pose a risk both to the pregnant person and the fetus. The risks of these procedures can include infections, Rh sensitization — an inflammatory condition in which the pregnant person’s immune system attacks fetal blood cells — and, in rare cases, miscarriage.

Vigorous activity should be avoided for a day or two after prenatal testing. Slight cramping and spotting after CVS or amnio are normal, but immediate medical attention should be sought if there is vaginal bleeding, fluid leakage, uterine contractions, or fever.

What is newborn screening?

In the U.S., Canada, Australia, and in most of Europe, newborn infants are tested for a variety of health conditions before leaving the hospital. One of the diseases tested for is cystic fibrosis.

Newborn screening for CF is generally done on a blood sample obtained through a heel prick — a quick jab with a small needle in the baby’s heel.