Retrospective Cohort Analysis of Perinatal Outcomes Following Bariatric Surgery

By Maria F. Gallo, PhD

Professor and Associate Dean of Research, College of Public Health, Division of Epidemiology, The Ohio State University, Columbus

SYNOPSIS: In a retrospective study of a racially and ethnically diverse cohort in 2012-2018, patients with a live birth after bariatric surgery had a lower risk of preeclampsia, gestational diabetes or impaired fasting glucose, and having a large-for-gestational-age infant — but a higher risk of having a small-for-gestational-age infant — relative to matched controls who did not have bariatric surgery before their live birth.

SOURCE: Boller MJ, Xu F, Lee C, et al. Perinatal outcomes after bariatric surgery compared with a matched control group. Obstet Gynecol 2023;141:583-591.

Obesity has increased dramatically in recent decades. By 2021, one-third of adult women of child-bearing age in the United States were obese.¹ Obesity in pregnancy is a concern because it increases health risks for both the gestational parent and the infant. These include increased risk of gestational diabetes, hypertension, preeclampsia, cesarean delivery, pre- and post-term delivery, infants of small- and large-for-gestational-age, and infant death. Future risks to the offspring also include metabolic syndrome and childhood obesity.

Bariatric surgery is the most effective treatment for weight loss for severely obese people who have not been able to lose weight with diet and exercise.² Compared with nonsurgical treatments, bariatric surgery also appears to lead to better control of hypertension and diabetes. It could, though, have adverse effects on a future pregnancy. These might differ by the type of bariatric surgery. Sleeve gastrectomy, which restricts the capacity of the stomach, is the most common type performed in the United States today.

The second most common, accounting for a much smaller fraction of cases, is Roux-en-Y gastric bypass. By bypassing the small intestine, this type can interfere with the absorption of micronutrients. The best timing of pregnancy after bariatric surgery is not known; however, most recommendations are to wait at least 12 to 24 months to conceive. This delay is to avoid getting pregnant during the period immediately after bariatric surgery when most people have rapid weight loss and have not yet reached their target weight.

Boller and colleagues carried out a retrospective cohort study to compare the perinatal outcomes of live births that occurred among people who had undergone bariatric surgery with those of matched controls without this surgery history. To do this, the authors used electronic health records from a large integrated healthcare system in 14 counties in Northern California that had 16 delivery hospitals and more than 40 outpatient clinics. There were 270,476 live births in these records for the study period of 2012-2018. Of these, 1,591 were singleton pregnancies resulting in a live birth that occurred among the 1,362 patients with a history of bariatric surgery.

The authors used propensity scores to match each case to five control pregnancies that resulted in a live birth among patients without a history of bariatric surgery. This yielded 7,955 control pregnancies from 7,814 patients. The control pregnancies were matched on propensity scores based on age at delivery, prepregnancy body mass index (BMI), delivery year, parity, neighborhood deprivation index, race and ethnicity, insurance status, initiation of prenatal visit in the first trimester, smoking during pregnancy, chronic hypertension, and prepregnancy diabetes. The study data came from the electronic health records, which included records of diagnostic or procedural codes, supplemented when possible by other clinical data, such as the internal bariatric surgery dashboard.

The authors had seven primary outcomes for perinatal health: preterm birth, gestational hypertension, preeclampsia, glucose tolerance status, infants of small- and large-for-gestational-age, and cesarean birth. Preterm birth was defined as those occurring before 37 weeks of gestation. Those without prepregnancy diabetes, and thus at risk of gestational diabetes mellitus, were assessed using a standard oral glucose tolerance test. This test, though, often is not well tolerated after bariatric surgery.³ Thus, the authors also used alternative test results based on abnormal fasting glucose levels. Small- and large-for-gestational-age were defined as being at or below the 10th percentile or at or above the 90th percentile, respectively, using sex and gestational age-specific distributions. They used modified Poisson regression to calculate unadjusted and adjusted relative risks (aRR) to compare pregnancies following bariatric surgery to control pregnancies, accounting for the factors included in the propensity score calculations and the fact that some patients had multiple pregnancies included in the analysis.

The patients who had undergone bariatric surgery had an average age of 34 years, had an average BMI at pregnancy onset of 34, and represented a diverse range of racial and ethnic groups. The propensity score matching resulted in the two groups — those with and without a history of bariatric surgery — being well-matched. In the adjusted analyses, pregnancy after bariatric surgery was linked with a lower risk of preeclampsia (aRR, 0.72; 95% confidence interval [CI], 0.60-0.86), gestational diabetes or impaired fasting glucose (aRR, 0.73; 95% CI, 0.66-0.80), and large-for-gestational age (aRR, 0.56; 95% CI, 0.48-0.65). However, pregnancy after bariatric surgery was associated with a higher risk of small-for-gestational-age (aRR, 1.51; 95% CI, 1.28-1.78). No differences between the groups were found for the other primary outcomes of preterm birth, gestational hypertension, and cesarean delivery. The findings still were observed when assessed separately by type of bariatric surgery (sleeve gastrectomy and Roux-en-Y gastric bypass) and time since surgery (more than two years and two or fewer years).

COMMENTARY

A meta-analysis published in 2019 compared perinatal outcomes among those who had undergone bariatric surgery with those without this surgery history.⁴ By pooling the data from 33 studies, the authors found that pregnancy after bariatric surgery was linked with higher occurrence of perinatal mortality, preterm birth, and congenital anomalies. Boller and colleagues did not evaluate perinatal death and congenital anomalies. The choice of outcomes to include in a study is important. Ideally, analyses on this topic would include a full range of positive and negative outcomes to help people weigh their various risks and benefits.

The meta-analysis also found that those who had a bariatric surgery type that interferes with absorption were more likely to have a small infant and were less likely to have a large infant.⁴ These differences in infant size, though, were not seen for those who used a restrictive bariatric surgery type. Boller and colleagues also found that pregnancies following bariatric surgery were more likely to have a small-for-gestational-age and less likely to have a large-for-gestational-age infant. However, their findings held regardless of whether the person had Roux-en-Y gastric bypass (i.e., surgery that interferes with absorption) or sleeve gastrectomy (i.e., surgery that limits stomach capacity). Their findings, though, were limited in that they only had data on bariatric surgery (type and time between bariatric surgery and pregnancy) for the 51% of patients with bariatric surgery who had this performed within the study health system. It is important for future studies to collect more complete data on the bariatric surgery. The findings by Boller and colleagues did not differ by whether the pregnancy was within two years after the surgery vs. more than two years. However, it could be that assessing by two years is too crude of a division to find differences by time since surgery. It also could be that weight stabilization — and not time since bariatric surgery — is the important factor to consider.

Boller and colleagues studied perinatal outcomes from live births that occurred among those who had bariatric surgery compared to matched controls who did not. It is important to note that they did not try to determine the perinatal outcomes that would have occurred to someone had the person never undergone bariatric surgery. That is, they did not set out to answer the question of whether someone should have bariatric surgery before becoming pregnant. In this case, without having bariatric surgery, the person likely would have entered pregnancy at a higher weight and, thus, would be expected to have worse outcomes.

Instead, the authors wanted to better understand the effect of a history of bariatric surgery on perinatal outcomes. To do this, they performed propensity score matching, using a wide range of factors, including pre-pregnancy weight, to compare patients who had undergone bariatric surgery with their counterparts without a history of this surgery. This approach is a key strength of the analysis. By using propensity score matching to try to make the two groups comparable except for the history of bariatric surgery, the authors attempted to isolate the effect of having a history of bariatric surgery on the pregnancy. Despite this, though, the two groups still might not have been comparable. It is entirely possible that the patients who had undergone bariatric surgery differed in some fundamental ways from the patients without this history and that these unmeasured differences could affect perinatal outcomes.

Overall, these findings suggest that regardless of the type of bariatric surgery used, patients who become pregnant afterward should be carefully counseled regarding diet and nutrition. At the same time, providers must ensure that their care of pregnancy patients following bariatric surgery does not contribute to stigma about body weight, which remains a prevalent issue in our healthcare system.

REFERENCES

1. March of Dimes Peristats. Behavioral Risk Factor Surveillance System, Centers for Disease Control and Prevention. www.marchofdimes.org/peristats
2. Arterburn DE, Telem DA, Kushner RF, Courcoulas AP. Benefits and risks of bariatric surgery in adults: A review. JAMA 2020;324:879-887.
3. Benhalima K, Minschart C, Ceulemans D, et al. Screening and management of gestational diabetes mellitus after bariatric surgery. Nutrients 2018;10:1479.
4. Akhter Z, Rankin J, Ceulemans D, et al. Pregnancy after bariatric surgery and adverse perinatal outcomes: A systematic review and meta-analysis. PLoS Med 2019;16:e1002866.