Bariatric surgery can offer a variety of benefits to mothers and improve neonatal outcomes but also offers substantial risk, according to a systematic literature review.

“Bariatric surgery, with patients matched for presurgery body mass index [BMI], resulted in a reduction in gestational diabetes mellitus, large-for-gestational-age infants, large babies (composite of large for gestational age and macrosomia), gestational hypertension, all hypertensive disorders, postpartum hemorrhage, and cesarean delivery rates,” wrote Wilson Kwong, MD, of the University of Toronto, and his colleagues. “However, there was an increase in small-for-gestational age infants, intrauterine growth restriction, small babies (composite of small for gestational age and intrauterine growth restriction), and preterm deliveries.”

Dr. Kwong and his research team developed this study to investigate the benefits and risks of bariatric surgery on neonatal outcomes. They designed a systematic review that involved a literature search of 2,616 abstracts using MEDLINE, Embase, Cochrane, Web of Science, and PubMed. They searched all from initiation of the databases to Dec. 12, 2016. Ultimately, this yielded 20 cohort studies and approximately 2.8 million subjects for review and meta-analysis. From this data, pooled odds ratios were estimated, as well as the number needed to benefit (NNTB) and the number need to harm (NNTH) to display the pooled absolute risk difference.

The results of the primary analysis, in which BMIs were similar between control subjects and the presurgery BMIs of women receiving treatment, yielded positives for mothers who underwent bariatric surgery and their newborns. As stated by Dr. Kwong and his research team, newborns were less likely to be large-for-gestational-age babies or deal with macrosomia (odds ratio, 0.36; 95% confidence interval, 0.20-0.66; NNTB, 7) and mothers were less likely to experience hypertensive disorders (OR, 0.38; 95% CI, 0.27-0.53, NNTB, 8) and postpartum hemorrhage (OR, 0.32; 95% CI, 0.08-1.37; NNTB, 9).

Despite the positives, the risk for harm was higher in a number of outcomes. Babies were more likely to be small for gestational age, have intrauterine growth restriction (OR, 2.16; 95% CI, 1.34-3.48; NNTH, 21) ,and be delivered preterm (OR, 1.35; 95% CI, 1.02-1.79; NNTH, 35).

A secondary analysis revealed that malabsorptive surgeries resulted in a significantly greater decrease (P = .012) in large babies (OR, 0.28; 95% CI, 0.22-0.36), compared with restrictive surgeries (OR, 0.50; 95% CI, 0.35-0.73). This analysis also revealed that malabsorptive bariatric surgeries corresponded to an increase in the number of small babies (OR, 2.39; 95% CI, 1.94-2.94; P = .023).

The increased risk of smaller babies may be caused by micronutrient deficiencies in pregnancy, according to Dr. Kwong. Nutritional deficiencies are reported in up to 80% of bariatric surgery patients, malabsorptive patients in particular.

“Common nutrient deficiencies after bariatric surgery include protein, B vitamins, fat-soluble vitamins, essential fatty acids, and minerals (zinc and copper), which may persist throughout pregnancy,” wrote Dr. Kwong and his colleagues.

Similar nutrient deficiencies have been identified in a case study of a woman who underwent a duodenal switch published in the Journal of Obstetrics & Gynaecology Canada. After several failed pregnancies from complications from malnutrition, the patient presented herself to physicians 10 weeks into her next pregnancy and was found to be deficient in vitamins A, D, E, and K, and minerals iron and zinc. After supplementation with a daily nutritional drink containing vitamins and protein, her vitamin levels were near normal at week 24. She eventually delivered a healthy newborn with normal-appearing features. The researchers from this study recommended that patients seeking bariatric surgery should avoid malabsorptive surgeries and defer to less extreme surgical methods.

A strength of the systematic review was the matching of studies based on presurgery and prepregnancy BMI. This was a departure from previous studies that combined all studies. Additionally, this study compared the outcomes based on the type of data source that was used. Despite these strengths, the design and results of the studies in the analysis limited the results of the review. None of the included studies were randomized; instead, they consisted of observational cohort studies, which are prone for confounding by indication.

“In counseling patients of childbearing potential who are interested in pursuing bariatric surgery, a discussion of both possible benefits and risks on pregnancy outcomes must take place,” cautioned Dr. Kwong and his associates. “Future studies should explore the causes of these potential adverse pregnancy outcomes and develop strategies that may prevent them.”

All authors affiliated with the study had no relevant financial conflicts of interest to report.

SOURCE: Kwong W et al. Am J Obstet Gynecol. 2018 Feb 15. doi: 10.1016/j.ajog.2018.02.003 .


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