Infants of women who have had weight loss surgery are more likely to be born premature and small in size for their gestational age, compared with babies born to women who have not had weight loss surgery. This is according to a study published in the BMJ.

Researchers from the Karolinska Institutet in Sweden say their findings show that pregnancies for women who have undergone weight loss (bariatric) surgery should be treated as high-risk pregnancies and that these women should receive more attentive prenatal care.

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Researchers say that infants of women who have had weight loss surgery are more likely to be born premature, and these type of pregnancies should be classed as ‘high risk.’

A 2010 study from the University of Texas Southwestern Medical Center in Dallas revealed that there are approximately 113,000 cases of bariatric surgery in the US every year. According to the researchers, most of these operations are performed on women, meaning that the number of babies who are born to women who have had weight loss procedures is also on the rise.

For their study, the investigators analyzed 2,500 babies who were born between 1992 and 2009. All of these infants were born to women who had undergone bariatric surgery. These were compared with 12,500 babies of mothers who had not had bariatric surgery.

The researchers matched the pregnancies individually, meaning that in each group, the mothers’ body mass index (BMI), age, educational background, smoking habits and previous births were comparable.

The findings revealed that 5.2% of babies born to women who underwent bariatric surgery were small for gestational age, compared with 3% of babies who were born to mothers who did not have bariatric surgery.

It was found that 4.2% of infants born to mothers who had bariatric surgery were large for gestational age, compared with 7.3% of babies in the control group.

Furthermore, 9.7% of infants were born prematurely (before the 37th week) to mothers who had weight loss surgery, compared with 6.1% in the control group.

The investigators found no difference between the groups regarding stillbirth or neonatal death within the first 27 days after birth.

Explaining the findings, Dr. Olof Stephansson, of the Clinical Epidemiology Unit at Karolinska Institutet, says:

Mothers with the same BMI gave birth to babies of varying weights depending on whether or not they had undergone bariatric surgery, so there is some kind of association between the two.

The mechanism behind how surgery influences fetal growth we don’t yet know, but we do know that people who have bariatric surgery are at increased risk of micronutrient deficiencies.”

The investigators believe their findings indicate that women who have a history of bariatric surgery should be told about the risks that may arise as a result of their surgery, and they should be considered as a risk group when pregnant.

They note that care providers should pay close attention to these particular pregnancies, and the women should undergo additional ultrasounds to check fetal growth and be given special dietary supplement recommendations, if needed.

However, the researchers emphasize that aside from their findings, weight loss surgery also provides many benefits for mothers. Obesity is a known risk factor for both the baby and its mother during pregnancy, and bariatric surgery may reduce the risk of diabetes, cardiovascular disease, cancer and stroke.

Earlier this year Medical News Today reported on a study that suggested women who have had bariatric surgery should wait at least 1 year before becoming pregnant.