Complex congenital heart defects are less common today than previously in children with Down syndrome, Swedish researchers report.

“With the introduction of antenatal screening, many fetuses diagnosed with Down syndrome are aborted,” write Dr. Stefan Johansson of Karolinska Institutet in Stockholm and colleagues in Pediatrics, online June 1. Therefore, “little (was) known about the cardiovascular phenotype in infants with Down syndrome born today.”
To investigate whether risks of specific types of congenital heart defects changed among infants with Down syndrome when antenatal screening was introduced in Sweden, the researchers analyzed data from national health care registers covering the period 1992 to 2012.

They calculated risk ratios for congenital heart defects for each three-year period and adjusted for maternal age, parity, BMI, smoking, diabetes and hypertensive disease, and infant gender.

They found that a congenital heart defect was diagnosed in 54% of infants with Down syndrome. Although year of birth was not associated with the overall risk of any congenital heart defect, the risk of complex congenital heart defects decreased significantly over time.

Compared with 1992 to 1994, the risk in 2010 to 2012 was reduced by almost 40% (adjusted risk ratio, 0.62). By contrast, risks for isolated ventricular septal defect (VSD) or atrial septal defect showed significant increases during later years.

Overall, the three most common congenital heart defect diagnoses were atrioventricular septal defect (42%), VSD (22%) and atrial septal defect (16%). Although atrioventricular septal defect was far more common than VSD in 1992 to 1994, they were equally common in 2010 to 2012.
“Many parents whose newborn babies have Down syndrome are being informed that the risk of complicated heart malformations is high. Therefore, all infants with Down syndrome should undergo heart ultrasound after birth,” Dr. Johansson told Reuters Health by email.

“However, our study shows that the risk of a complicated heart malformation has dropped by 40%. Despite the same underlying genetic abnormality – a third copy of chromosome 21 – the ‘expression’ of Down syndrome has changed in a more favorable direction. The lower risk of complicated heart malformations likely leads to less need of thoracic surgery, a great advantage for many families and babies,” he said.

“Although we did not have access to such data, we speculate that the introduction of prenatal diagnostics of chromosomal abnormalities explains much of the risk reduction. Pregnancies complicated by both Down syndrome and a congenital heart defect may be more often terminated,” Dr. Johansson concludes.

Pediatric cardiologist Dr. Shaji C. Menon of the University of Utah, Salt Lake City, told Reuters Health by email, “The most important finding of this study was the significant reduction over time in the proportion of Down syndrome infants born with complex congenital heart defects like atrioventricular septal defect, while the proportion of infants with simple congenital heart defects like atrial septal defect and isolated ventricular septal defect increased.”

Like the authors, Dr. Menon noted that “this drastic reduction . . . is likely secondary to selective termination of a higher proportion of Down syndrome fetuses with complex congenital heart defects.”

He added, “Even with significant advancements in the management of Down syndrome and its associated defects, the selective termination rates of fetuses with Down syndrome have not decreased. For many parents, the challenges of raising a child with Down syndrome seem overwhelming. (But at the same time), there are couples who are on a waiting list for adopting a child with Down syndrome.”