Causes of major birth defects 'largely unknown'

31st May 2017 – The underlying reasons for most birth defects is still largely a mystery to doctors, say US scientists.

A research team led by the University of Utah School of Medicine in Salt Lake City, say in a group of infants, they were only able to establish a definite cause in just 1 in 5 cases.

They say their findings, published in the BMJ, "underscore the large gaps in current knowledge of the causes of birth defects".

Common and costly

In the US, major birth defects affect 1 in 33 births. The researchers say the problem is likely to be even more common as the figures don't take into account foetal deaths.

The cost of care in the US in 2004 was estimated at £2 billion.

Latest UK statistics suggest that around 1 baby in every 50 is born with some sort of birth defect. A report by the British Isles Network of Congenital Anomaly Registers (BINOCAR) in 2014 estimated that around 17,800 babies were born with birth defects in England and Wales in 2012.

Congenital heart defects affected around 6 in 1,000 births. Neural tube defects affected around 1 in 800 babies.

Risk factors

Studies have demonstrated links between birth defects and risk factors, including maternal diabetes, smoking and obesity. However, showing that these factors actually cause birth defects has proved more difficult.

The latest research is based on major birth defects in children born from 2005 to 2009 in the state of Utah in the western US. Among 270,878 births, 5,504 cases of birth defects were found – a rate of 2.03%.

A definite cause was found in only 20.2% of these cases, with chromosomal or genetic conditions accounting for 94.4% of cases. Environmental exposure was identified as a cause in 4.1% and conditions associated with twins were found in 1.4% of cases.

Among the 79.8% where no cause was identified, 88.2% were isolated birth defects, and only 4.8% were linked to a documented family history of similar defects.

'More quality research is needed'

Commenting on the research in an emailed statement, Professor Neena Modi, president of the Royal College of Paediatrics and Child Health, says: "This study was conducted in one area of the United States but the conclusions are relevant around the world.

"It is true that our knowledge on the causes of major birth defects remain incomplete. To drive improvements in pregnancy and newborn outcomes, more high quality research must be carried out in partnership with families, and in collaboration with scientists and clinicians internationally."