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Pregnancy after bariatric surgery reduced risk of poor outcomes

Women who had bariatric surgery and became pregnant had reduced risk of poor outcomes such as pre-eclampsia or gestational diabetes, compared with pregnant women who did not have the surgery. However, those who had surgery also had a greater chance their baby would be born small, according to a study, ‘Perinatal Outcomes After Bariatric Surgery Compared With a Matched Control Group’, published in Obstetrics & Gynecology, by researchers from Kaiser Permanente.

“Our study offers support for the safety of pregnancy after bariatric surgery,” said senior author, Dr Monique Hedderson, a research scientist with the Kaiser Permanente Division of Research. “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 foetal growth.”


We conducted a retrospective cohort study that evaluated perinatal outcomes in pregnant patients after bariatric surgery from January 2012 through December 2018. History of bariatric surgery was identified by using International Classification of Diseases codes and a clinical database. Primary outcomes were preterm birth (PTB), gestational hypertension, preeclampsia, impaired glucose tolerance or gestational diabetes, a large-for-gestational-age (LGA) or small-for-gestational-age (SGA) neonates, and caesarean birth.


Propensity scores were estimated by using logistic regression that accounted for age at delivery, pre-pregnancy body mass index, year of delivery, parity, neighbourhood deprivation index, race and ethnicity, insurance status, initiation of prenatal visit in the first trimester, smoking during pregnancy, chronic hypertension, and pre-existing diabetes. Five patients in the control group were matched to each patient in the case group on linear propensity score, and modified Poisson regression was used to adjust for covariates. Sensitivity analyses by timing and type of surgery were performed.


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 among those who had 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 caesarean delivery.


The results are relevant for patients who are planning pregnancy or bariatric surgery, said lead author Dr Marie Boller, an obstetrician/gynaecologist 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. 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.”

The finding about increased risk of small-for-gestational-age babies emphasises the importance of these patients working closely with their care team.


“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,” added Boller. 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, Dr Mara Greenberg, a maternal-foetal 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. “

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 as living with obesity.


“It seems there may be something beneficial about having had bariatric surgery even if you are obese at the start of your pregnancy,” said Hedderson. 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,” said Greenberg.

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 programme.

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