Is Mom's Bariatric Surgery Linked With Birth Defects?

F. Perry Wilson, MD, MSCE


October 16, 2019

Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I'm Dr F. Perry Wilson.

This week, Sweden.

Ah, Sweden. Birthplace of Bjorn Borg, harvesters of delicious gummy fish, and inventors of the dowel, I assume.

This Scandinavian paradise offers more than just meatballs. They have what may be the most comprehensive medical database of any country in the world. Sure, sure, Big Brother and all that, but the power of having detailed medical data from birth to death on an entire population is an epidemiologist's dream. And this week, a Swedish study appearing in JAMA[1] gives us an answer to a question that we really couldn't get any other way: Does bariatric surgery increase the risk of the patient's child having birth defects?

It's an important question. There are ample data to suggest that gastric bypass surgery can lead to folate deficiency, and in theory, that could increase the risk for neural tube defects. There are other malabsorptive syndromes as well that may have untold fetal effects. On the other hand, better control of metabolic syndrome, hyperinsulinemia, and blood glucose might actually reduce the risk for birth defects.

And here's why you need Swedish data. Let's concede that no one is going to take obese pregnant women and randomize them to bariatric surgery or usual care while they are pregnant. You could potentially randomize people to surgery before they become pregnant, but that’s a pretty huge trial to ensure that you'd capture enough pregnancies to say anything.

So we're left with observational data. But this is tricky. Women who undergo bariatric surgery are different from women who don't, making finding a control group really difficult. With Swedish data, though—well, check it out.

Researchers led by Dr Martin Neovius identified all live births in Sweden from 2007 to 2014 and linked them to a registry of all women who had Roux-en-Y gastric bypass surgery in that time period—because they could.

They then searched all other women who had given birth for potential controls, matching on BMI, diabetes, delivery year, age, smoking, substance abuse, parity, psychiatric drugs, and number of prescription drugs. I'm so jealous.

What they found was pretty clear. Women who underwent bariatric surgery before becoming pregnant had a lower risk of giving birth to a child with birth defects.


This association held when examining just the first births after surgery and after excluding births with chromosomal abnormalities. Importantly, there were zero cases of neural tube defects in the surgery group and 20 in the control group.

In fact, the overall rate of major birth defects in the surgery group (3.5%) was basically the same as in the general population.

Now, we have to be a bit careful here. This study only examined live births. You could posit that surgery may have increased the rate of fetal loss, perhaps putting some selective pressure on "healthier" babies, but this feels like a stretch to me. Also, remember that this study only looked at Roux-en-Y bypass; it doesn't say anything about gastric banding or sleeves.

But basically, I think we have once again seen that bariatric surgery carries substantial benefit. Though it is essentially the riskiest weight loss option, it may also be the most effective—for the patient and their children.

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and director of Yale's Program of Applied Translational Research. Dr Wilson's lab focuses on interventional data science, and he holds multiple grants to study ways in which real-time data can be leveraged to improve patient outcomes. He has an extensive body of peer-reviewed literature and has published in The Lancet, JAMA Internal Medicine, the Journal of the American Society of Nephrology, PLOS One, PLOS Medicine, and the Journal of Clinical Investigation. He is committed to helping clinicians and the lay public understand the medical literature and its nuances, foibles, and successes. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. He tweets @methodsmanmd and hosts a repository of his communication work at

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