A study by researchers in the UK found that being obese in pregnancy raised the chances of women having babies with birth defects including spina bifida, cleft lip and palate and other congenital abnormalities such as malformed limbs. The researchers stressed however that despite their findings, the rates at which these occur are still very small.

The study was the work of Dr Katherine J Stothard and colleagues from Newcastle University, Newcastle upon Tyne, UK, and is published in the February 11 issue of JAMA, Journal of the American Medical Asssociation.

Congenital abnormalities are a leading cause of stillbirth and infant death, accounting for 1 in 5 deaths among infants in the US, and they contribute to preterm birth and childhood illnesses, wrote the authors in their background information.

While no national figures available, a recent study suggests that up to one fifth of pregnant women are classed as obese in the UK, and as many as one in three women over the age of 15 in the US was obese in 2004, they said in a separate press statement.

According to the World Health Organization, you are classed as obese if your Body Mass Index (BMI, the ratio of your weight in kilos to the square of your height in metres) is over 30. You are classed as overweight if your BMI is over 25.

Co-author Dr Judith Rankin said:

“Women who are thinking about trying for a baby need to check their own weight first and then think about seeking help if they are overweight.”

She said during pregnancy was not the right time to start a weight loss diet; it was more important to eat healthily and sensibly.

The researchers found that women who were obese had more than twice the risk of having a baby with spina bifida, a rare condition that may result in disability.

For the meta-analytical study they reviewed studies that looked at the risk of birth defects in babies born to obese or overweight mothers.

They found the studies by searching a number of medical databases for studies published between 1966 and 2008 and also looked at reference lists of relevant review articles.

The researchers only included observational studies where women’s early or pre-pregnancy weight or BMI was known or estimated and there was data on congenital abnormalities. Of 1,944 articles that met their criteria, 39 were systematically reviewed and the results from 18 were pooled for the meta-analysis.

The results showed that:

  • Compared to mothers of recommended BMI, obese mothers were nearly twice as likely to have a baby with neural tube defects (caused by the incomplete development of the brain, spinal cord and/or their protective coverings).
  • For one neural tube defect, spina bifida, the risk was more than doubled.
  • There was also an increased risk of heart defects (cardiovascular anomaly), cleft lip and palate, malformation of lower bowel (anorectal atresia), water in the brain (hydrocephaly) and malformed arms and legs (limb reduction anomaly).
  • The risk of gastroschisis however was significantly reduced (where the fetus develops a hole in the abdomen).

The study concluded that:

“Maternal obesity is associated with an increased risk of a range of structural anomalies, although the absolute increase is likely to be small.”

There was also some evidence that being overweight in pregnancy raised the chances of having a baby with neural tube defects, but the researchers said more studies were needed to confirm this.

Rankin said:

“This is the first time that so many studies have been combined to build a more accurate picture and it shows a link between a mother’s weight and many of these serious conditions in the newborn baby.”

“Given that we are seeing an increase in the number of people who are overweight or obese, then we may see an increase in the number of babies born with abnormalities,” she added.

Despite these findings, however, the researchers said that the abnormalities are uncommon:

“Spina bifida only occurs in approximately one in every two thousand births, so the risk, even among obese women, remains very low,” they stressed.

“Maternal Overweight and Obesity and the Risk of Congenital Anomalies: A Systematic Review and Meta-analysis.”
Katherine J. Stothard; Peter W. G. Tennant; Ruth Bell; Judith Rankin.
JAMA Vol. 301 No. 6, pp 636-650, February 11, 2009.

Click here for Abstract.

Sources: Journal abstract, JAMA news release, Newcastle University.

Written by: Catharine Paddock, PhD