The risks of major birth defects during the first year of an infant’s life progressively increase with a mother’s levels of being overweight or obese, according to Swedish researchers.
As a result, they said efforts should be made to encourage women of reproductive age to adopt a healthy lifestyle and to obtain a normal body weight before conception.
“Efforts should be made to encourage women of reproductive age to adopt a healthy lifestyle”
It is already known that maternal obesity increases risks of congenital malformations, noted the study authors from Karolinska Institute.
But it was previously not yet clear, they said, if the risks were increased in offspring of overweight mothers and if risks increase with increasing severity of obesity.
They analysed information on more than 1.2 million live singleton births in Sweden recorded in the medical birth register between 2001 and 2014.
Data on maternal and pregnancy characteristics were recorded, as were details of any major congenital malformation and several organ specific malformations diagnosed during the first year of life.
The researchers defined mothers as being underweight, with a body mass index of less than 18.5, normal weight (BMI 18.5 to 24), overweight (BMI 25 to 29) or obese – either classe I (BMI 30 to 34), II (BMI 35 to 39) or III (BMI 40 or over).
Around 3.5% of the offspring had a major congenital malformation. Heart defects were the most common malformation, followed by those of the genital organs, limbs, urinary system, digestive system, and nervous system.
“Midwives are ideally placed to support and advise women about healthy eating”
The researchers found that, overall, the risk of malformations among the offspring of normal weight mothers was 3.4%.
Among the offspring of mothers who were overweight the risk was 3.5%, while for those who were obesity class I it was 3.8%, for class II it was 4.2% and for class III it was 4.7%.
The risks of congenital heart defects, malformations of the nervous system, and limb defects also progressively increased with BMI from overweight to obesity class III.
Malformations of the genital and digestive systems were also increased in offspring of obese mothers, noted the researchers.
They said their results “underline the importance of having a maternal BMI in the normal range before pregnancy”.
“Efforts should be made to encourage women of reproductive age to adopt a healthy lifestyle and to obtain a normal body weight before conception,” they said in the British Medical Journal.
Jacque Gerrard, director for England at the Royal College of Midwives, said the study built on previous research about the impact of being overweight or obese on the developing baby.
“Adult and childhood obesity is a major problem in the UK which is known to increase the risk of developing other associated disease such as diabetes, hypertension and cardiovascular disease,” she noted.
Birth defect risk rises with mother’s obesity severity
“This latest research, published by the BMJ, suggests that there is an increased risk of birth defects where women are overweight or severely obese, and healthcare professionals have a role in informing women and their families about the risks,” she said.
“In particular, midwives are ideally placed to support and advise women about healthy eating and weight gain during pregnancy,” she said. “We also know that this is best received where the midwife has already formed a positive relationship with the women in models of care such as continuity of carer where it is well evidenced that this improves health outcomes.
Ms Gerrard highlighted that, between pregnancies, weight loss programmes combined with exercise had been shown to be helpful and that “midwives may signpost women to these”.
She added: “There is a need for greater priority to be placed on prevention interventions including giving women evidence based information, education and also support for women and their families, about the benefits of healthy eating before and during pregnancy, and taking appropriate exercise.
“More emphasis also needs to be placed on pre-conceptual care,” she said. “We need to see more effort and resources put into reducing obesity generally in the population, and in the services available to women who are planning a family or already pregnant”.