Prenatal Testing for Cystic Fibrosis Influences Pregnancy Outcomes, Review Finds

Prenatal genetic testing for cystic fibrosis (CF) significantly influences how women manage their pregnancies, with positive tests linked to high rates of pregnancy terminations, a systematic review study finds.

The study, “Prenatal genetic testing for cystic fibrosis: a systematic review of clinical effectiveness and an ethics review,” was published in the journal Genetics in Medicine.

Prenatal screening for mutations in the CFTR gene — the root of CF development — is performed when a fetus has a high risk for inheriting the disease. This is the case when both parents carry CF-causing genetic mutations, which represents a 25% risk of their descendants developing CF — a 625-times higher risk than the general population.

CF prenatal testing is also performed when ultrasound assessment in the second trimester shows fetal echogenic bowel — when the bowel appears to be brighter than normal in the imaging test. Studies suggest that 0.8%–13.3% of fetuses that have echogenic bowels will have CF.

Prenatal testing is performed either by chorionic villus sampling (analysis of a small sample of cells from the placenta) or by amniocentesis (analysis of fluid that surrounds the fetus in the womb). Non-invasive procedures, such as the analysis of cell-free DNA circulating in the mother’s blood, is becoming more commonly used in the clinic.

In the study, Australian researchers reviewed the data of 19 previously published studies on diagnostic performance and changes in CF management after testing to better understand the clinical value of prenatal CF screening.

The team found that 8%–22% of the fetuses from parents carrying one CFTR variant were also positive for genetic mutations in both alleles (the gene copies inherited from the father and mother). The screenings also detected 38%–58% of carrier cases (those who had only one copy of the CFTR mutation), while 24%–33% were negative for any CFTR variant.

Two studies in which fetal echogenic bowel was detected, prenatal testing determined that 94% of the cases were negative for CF-causing mutations, and 6% of fetuses were identified as positive carriers.

In general, the studies had a low rate of diagnostic failure, with a median rate of approximately 4.5%, which could be easily overcome by performing additional genetic sequencing tests or by repeating the analysis, the researchers said.

Their study revealed that in cases of high CF risk (both parents being carriers) and in which screenings revealed that the fetus had CF, 94.6% of the pregnancies were terminated.

Pregnancy termination rate was lower (65%) in cases where CF was diagnosed prenatally after fetal echogenic bowel, and parents were not known carriers.

These findings show that prenatal “CFTR testing does influence patient management, very often leading to [termination of pregnancy] when the test result is positive,” the researchers wrote.

Pregnancy termination after prenatal CF diagnosis was shown to have significant psychological impact on the women. Most common symptoms were grief (36%–78%), post-traumatic stress (45.8%–67%), and depression (approximately 30%) in the first months after terminating pregnancy. These symptoms alleviated over time.

Similar psychological outcomes were observed in women who had a child with CF, with reports stating that 48% experience anxiety, and 20%–34% score positive for depression.

“The psychological impact of prenatal testing, and any subsequent decisions, requires further research,” the researchers said.

“There are concerns that prenatal testing may degrade society’s willingness to accept and care for children with CF. This is one important reason why the success of testing ought not to be gauged in terms of the number of CF births prevented,” they stated. “Prenatal testing for fetal abnormalities should instead serve the aim of providing pregnant women and couples with information to enhance their autonomy.”

“Nondirective counseling is crucial both for ensuring informed and voluntary consent to testing and for retaining the test’s aim of simply informing, rather than directing, reproductive choices,” they said.