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Women who have undergone obesity surgery should be classed as at-risk during pregnancy, say research

Increased risk of small babies but lower risk of large babies

BMJ

Research: Perinatal outcomes after bariatric surgery: nationwide population based matched cohort study

Women with a history of obesity surgery are at increased risk of giving birth to preterm or small-for-gestational age babies and should be regarded as an at-risk group, a paper published on bmj.com today suggests.

In 2008, an estimated 0.5 billion people were obese globally. Obesity is estimated to result in a 2-4 year shorter life span which increases to 8-10 years in those morbidly obese. Obesity is a risk factor for adverse pregnancy and perinatal outcomes (relating to the time immediately before and after birth).

Weight reduction is imperative to improve maternal health and bariatric surgery (the branch of medicine that deals with the causes, prevention, and treatment of obesity) is currently the most effective method. Its use has increased rapidly since the 1990s.

Researchers from the Karolinska Institute in Sweden therefore conducted a population-based study to evaluate the association between bariatric surgery and perinatal outcomes between 1992 and 2009. They used data from the Swedish Medical Birth Register, the National Patient Register and the Education Register. Women who had undergone bariatric surgery were compared with matched control births of fertile women without such history.

Data were retrieved on maternal age, early pregnancy BMI, smoking, delivery year, diabetes and pre-pregnancy hypertension. BMI was categorized as underweight (less than 18.5), normal weight (18.5-24.9), overweight (25.0-29.9) and obesity class I, II or III (30.0-34.9, 35.0-39.9, more than or equal to 40.0).

From 1992 to 2009, the number of births following bariatric surgery increased from 83 to 266. The average surgery to delivery time was 5.2 years.

Women with bariatric surgery history were older, more often obese, had lower education and were more often smokers. Following the matching of the control group, the researchers were left with 2534 post-bariatric surgery births compared with 12,468 control births of similar age, parity, early pregnancy BMI, smoking status, education level and delivery year.

Preterm birth was observed in 243 out of 2511 (nearly 10%) post-surgery births compared with 6.1% in the control group. The risk of having a small-for-gestational age baby was also higher in women with bariatric surgery (5% versus 3%). The opposite was true for large-for-gestational age babies.

The highest risk of preterm birth was observed in women with both bariatric surgery history and an early pregnancy BMI of equal to or less than 30 (overweight), followed by BMI 30-34.9 (obesity class I). There was no increased risk observed in women with BMI over or equal to 35.

The researchers conclude that pregnant women with bariatric surgery history "should be regarded as a risk group and be counselled regarding the increased risk of preterm birth". They suggest that further studies should investigate the causes behind the increased risk of small-for-gestational age births.

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