Birth defect risk 'rises with weight of mothers'

15th June 2017 – Pregnancy specialists advise mums-to-be to achieve a healthy weight to avoid health complications. Now, a new study links a mother being overweight or obese to a higher risk of major birth defects during a baby’s first year of life.

Swedish researchers say the findings reinforce the message that women should adopt a healthy lifestyle and make sure they are a healthy weight before they conceive.

Obesity epidemic

Obesity has reached epidemic proportions worldwide and has become a major health concern in pregnancy. Rates of severe obesity, defined as having a body mass index (BMI) of 35 or more, is becoming more common in particular.

Previous studies have shown that maternal obesity increases the risk of birth defects.

For the latest study, researchers from the Karolinska Institute in Sweden, set out to address 2 unanswered questions - whether the risk of birth defects increases in line with the severity of obesity and whether it also increases risk for mothers who are overweight, with a BMI between 25 and 29.

Swedish birth register

They analysed information on more than 1.2 million live singleton births in Sweden between 2001 and 2014 and linked information about the mothers and their pregnancies with any major birth defects diagnosed in their offspring before their 1^st birthday.

They found that 3.5% of the babies had major birth defects, with heart defects the most common, followed by defects of the genitals, limbs and urinary system.

The researchers found that, compared with offspring of healthy weight mothers, where the risk of major birth defects was 3.4%, the proportions of birth defects among the offspring of mothers with higher BMI were:

• 3.5% among overweight mothers
• 3.8% among obese mothers with a BMI of 30 to 34
• 4.2% among obese mothers with a BMI of 35 to 39
• 4.7% among obese mothers with a BMI of 40 or over

The overall risk of major birth defects was found to be higher in boys at 4.1% compared with 2.8% for girls.

The risk of defects to the heart, nervous system and limbs increased progressively as BMI increased from overweight to severe obesity, the researchers say.

The authors point out that the observational nature of their study means they cannot prove cause and effect.

'Real risks'

Commenting on the findings by email, Professor Russell Viner, officer for health promotion at the Royal College of Paediatrics and Child Health, says: "This is high quality research which, whilst observational, confirms previous evidence that obesity in mothers carries real risks of malformations in their offspring.

"We know that obese mothers have higher risks of a number of problems during pregnancy and labour and that their children have a higher risk of being obese themselves. We knew that maternal diabetes during pregnancy carried a risk of malformations. This study suggests that mothers who carry excess weight are increasing the risk of their baby having important malformations that will affect them lifelong or limit their life-span.