Pregnancy Outcomes Mixed After Bariatric Surgery

Factors Affecting Follow-Up in Women With Gestational Diabetes
Factors Affecting Follow-Up in Women With Gestational Diabetes
Bariatric surgery was associated with lower risks for some pregnancy complications and outcomes, but higher risks for others.

When compared with matched controls, pregnant women with a history of bariatric surgery had lower rates of gestational diabetes and excessive fetal growth, but were at increased risk for small-for-gestational age infants and shorter gestation.

There was also a trend toward a higher rate of stillbirth or neonatal death in women who had previously undergone bariatric surgery.

Results of the nationwide, prospective cohort study were published recently in the New England Journal of Medicine.

In all, researchers identified 627,693 singleton pregnancies between 2006 and 2011 from the Swedish Medical Birth Register. Of these pregnancies, 670 occurred in women who had previously undergone bariatric surgery and had pre-surgery weight recorded.

Each pregnancy in women who underwent bariatric surgery was matched with up to five control pregnancies in terms of pre-surgery BMI (early-pregnancy BMI was used in controls), age, parity, smoking history, educational level and year of delivery.

“The effects of bariatric surgery on health outcomes such as diabetes and cardiovascular disease have been studied, but less is known about the effects on pregnancy and perinatal outcomes,” lead study author, Kari Johansson, PhD, from the Department of Medicine in Solna, said in a press release.

“Therefore we wanted to investigate if the surgery influenced in any way the risk of gestational diabetes, preterm birth, stillbirth, if the baby was small or large for its gestational age, congenital malformations and neonatal death.”

Compared with matched controls, women who had pregnancies after bariatric surgery were at lower risk for gestational diabetes (1.9% vs. 6.8%; OR=0.25; 95% CI, 0.13-0.47) and large-for-gestational-age infants (8.6% vs. 22.4%; OR=0.33; 95% CI, 0.24-0.44).

However, pregnancies after bariatric surgery were also associated with higher risks for small-for-gestational-age infants (15.6% vs. 7.6%; OR=2.20; 95% CI, 1.64-2.95) and shorter gestation (273 vs. 277.5 days; mean difference, –4.5 days; 95% CI, −2.9 to −6.0). Despite this, the rate of preterm birth did not significantly differ between groups (bariatric surgery, 10% vs. control, 7.5%; OR=1.28; 95% CI, 0.92-1.78).

Furthermore, there was also a trend toward a higher rate of stillbirth or neonatal death in the bariatric surgery arm (1.7% vs. 0.7%; OR=2.39; 95% CI, 0.98-5.85), whereas the rate of congenital malformations was comparable between groups. 

“Since bariatric surgery followed by pregnancy has both positive and negative effects, these women, when expecting, should be regarded as risk pregnancies,” Dr. Johansson said. “They ought to be given special care from the maternal health services, such as extra ultrasound scans to monitor fetal growth, detailed dietary advice that includes checking the intake of the necessary post-surgery supplements.”

The researchers noted, however, that several potential study limitations exist, including selection bias; the observational nature of the study, which made it impossible to determine cause and effect; and the Swedish population enrolled, which was mostly white and thus the results may not be generalizable to other races.

In an accompanying editorial, Aaron B. Caughey, MD, PhD, from the department of obstetrics and gynecology at the Oregon Health and Science University, Portland, wrote that obstetricians will most likely be seeing an increasing number of women who have undergone bariatric surgery before pregnancy.

“According to American College of Obstetricians and Gynecologists (ACOG) recommendations, such women should be advised to delay conceiving until 12 to 24 months after surgery, the period when the most rapid weight loss occurs,” he wrote. “Once women who have undergone bariatric surgery are pregnant, we need to know which type of surgery they had. In particular, those who have undergone the traditional Roux-en-Y gastric bypass surgery are at increased risk for protein, iron, vitamin B12, vitamin D and calcium deficiencies; screening for these deficiencies is recommended by the ACOG.”

Dr. Caughey added that the current study underscores that bariatric surgery has the potential to reduce the risks for gestational diabetes and large-for-gestational-age neonates, but is also associated with some risks in pregnancy.

“Decisions regarding bariatric surgery in women of reproductive age should take into account the benefits and risks associated with this not inconsequential procedure, in terms of both pregnancy and long-term health,” he wrote.


  1. Johansson K et al. N Engl J Med. 2015;372(9):877-878.
  2. Caughey AB et al. N Engl J Med. 2015;372(9):814-824.