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Pregnancy after bariatric surgery results in good birth outcomes

Kaiser Permanente research offers reassurance to people who want to have weight loss surgery before starting a pregnancy

People who had bariatric surgery to address obesity and later became pregnant had less risk of poor outcomes such as preeclampsia or gestational diabetes, in comparison with similar pregnant patients who did not have the surgery. However, those who had weight loss surgery also had a greater chance their baby would be born small, according to Kaiser Permanente research published in Obstetrics & Gynecology.

Monique Hedderson, PhD

The study adds to growing evidence of the safety of giving birth after weight loss surgery, while emphasizing the importance of nutritional guidance during pregnancy for these patients, said senior author Monique Hedderson, PhD, a research scientist with the Kaiser Permanente Division of Research.

“Our study offers support for the safety of pregnancy after bariatric surgery,” Hedderson said. “And it points to the fact that these pregnancies need to be monitored closely to make sure the women are getting adequate nutrition to ensure fetal growth.”

The study compared 1,591 pregnancies in patients who had weight loss surgery with 7,955 pregnancies for patients who had not had the procedures; the two groups were demographically and medically similar and had similar body mass index (BMI) when their pregnancies began. They included patients who had different types of bariatric surgery, such as Roux-en-Y, sleeve gastrectomy, and laparoscopic adjustable gastric banding.

The analysis found less risk of preeclampsia (a dangerous condition of high blood pressure in pregnancy) among those who’d had the surgery (7.5% vs. 10.2%), as well as less risk of gestational diabetes (23.5% vs. 35%) and large for gestational age baby (10.6% vs. 19.9%).

There were no differences between the groups in preterm birth, gestational hypertension, or cesarean delivery.

Marie Boller, MD

The results are relevant for patients who are planning pregnancy or bariatric surgery, said lead author Marie Boller, MD, an obstetrician/gynecologist with The Permanente Medical Group.

“Our study findings can inform conversations between clinicians and patients who are planning pregnancy or are pregnant after bariatric surgery,” she said. “Bariatric surgery is an effective and safe intervention that has been proven to help people lose weight and maintain that weight loss when other strategies haven’t worked. It can also improve or even resolve comorbid conditions such as diabetes.”

Post-surgery nutrition

The finding about increased risk of small-for-gestational-age babies emphasizes the importance of these patients working closely with their care team, Boller said. “Because bariatric surgery alters the way our bodies process the food we eat, people can develop nutritional deficiencies after surgery, and careful attention to supplementation of micronutrients is important,” she said. She noted that pregnant patients of Kaiser Permanente Northern California (KPNC) have access to a multidisciplinary care team —including doctors, nurses, and registered dieticians — with KPNC’s Regional Perinatal Service Center.

At the same time, the findings about infant size were nuanced, said co-author Mara Greenberg, MD, a maternal-fetal medicine specialist who co-directs the Regional Perinatal Service Center. She noted that while small babies were more likely in the surgery group, that rate (10%) was similar to that seen in the average population, while the comparison group’s rate of 6% was relatively low. “That’s a bit more reassuring,” she said.

Mara Greenberg, MD, maternal-fetal medicine specialist, The Permanente Medical Group.

One study insight that warrants further exploration came from the fact that BMIs were similar between study subjects who had surgery and those who did not, suggesting weight was not the only or most important factor in determining birth outcomes. The average BMI of all study subjects was 34, considered “obese.”

“It seems there may be something beneficial about having had bariatric surgery even if you are obese at the start of your pregnancy,” Hedderson said. Many factors other than BMI relate to metabolic health, including hormones, metabolism, lifestyle, and genetics, she noted.

Greenberg noted that there could be additional factors about patients who choose bariatric surgery that drive good outcomes, factors that could not be measured in the study.

Ultimately, she said, the study offers useful guidance for severely obese patients weighing their care options. “It will be helpful for patients and their medical teams to know that bringing one’s weight or BMI down to a certain level prior to pregnancy, via bariatric surgery, is likely to result in good pregnancy outcomes, even if one retains a degree of obesity after the surgery,” Greenberg said.

The study’s overall findings are similar to those from a study group at Kaiser Permanente Southern California, who reported in 2021 they had also found lower risk of preeclampsia, gestational diabetes, and neonatal intensive care unit referral in pregnancies after bariatric surgery.

This study was funded by The Permanente Medical Group Delivery Science & Applied Research program.

Additional co-authors were Fei Xu, MS, Catherine Lee, PhD, MS, and Sneha Sridhar, MPH, of the Division of Research.

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About the Kaiser Permanente Division of Research

The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit or follow us @KPDOR.

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