Bariatric Surgery: Does It Affect Pregnancy Outcomes?
Abstract & Commentary
By Rebecca H. Allen, MD, MPH
Assistant Professor, Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Women and Infants Hospital, Providence, RI
Dr. Allen reports no financial relationships relevant to this field of study.
Synopsis: In this large, retrospective cohort study, women with a history of bariatric surgery were at a small increased risk of both spontaneous and medically indicated preterm birth and small for gestational age births. However, this was only true among women with an early pregnancy body mass index < 35 kg/m2.
Source: Roos N, et al. Perinatal outcomes after bariatric surgery:
Nationwide population based matched cohort study. BMJ 2013:347:f6460 [Epub ahead of print].
This is a population-based, retrospective cohort study from swe-
den that evaluated the association between bariatric surgery and perinatal outcomes. The authors identified subjects through the national medical birth register (includes 98% of all births in Sweden) and the national patient register (includes information on hospital admissions and surgeries) by using each person's Swedish personal identity number. They were able to access data on weight at first prenatal visit, smoking, education level, age, parity, gestational diabetes, and pre-pregnancy hypertension. Bariatric surgeries were classified into gastric bypass, vertical banded gastroplasty, and gastric banding. Subjects were matched to controls with no history of bariatric surgery on age, parity, body mass index (BMI) in early pregnancy, smoking status, education level, and delivery year in a 5:1 ratio.
A total of 1,742,702 births were analyzed, of which 2562 occurred after bariatric surgery for the treatment of obesity. Type of surgery was divided approximately into one-third vertical banded gastroplasty, one-third gastric bypass, and one-third gastric banding. The surgery to delivery interval was < 1 year in 2.4%, 1-2 years in 16%, 2-5 years in 39%, and ≥ 5 years in 42% (median 4.2 years). Overall, 9.7% of births in the bariatric surgery group were preterm (< 37 weeks) compared to 6.1% in the matched controls (risk difference, 3.6%; 95% confidence interval [CI], 2.4-4.9%; P < 0.001). Of these, 4.5% in the bariatric group compared to 2.5% in the matched control group were medically indicated (P < 0.001) and 5.2% compared to 3.6% were spontaneous preterm births (P < 0.001). The risk of delivering a small for gestational age infant was higher in the bariatric group (5.2% vs 3.0%; risk difference, 2.2%; 95% CI, 1.3-3.2%; P < 0.001). Effect modification was seen with BMI level where the highest risk of preterm birth was in women who had bariatric surgery and a BMI < 35 kg/m2, but no increased risk was seen in women with a BMI of ≥ 35 kg/m2. Neither the type of bariatric surgery nor the interval between the bariatric surgery and the delivery affected the results. When the bariatric group was compared to a group of controls who would have been eligible for bariatric surgery based on their weight, the excess risk of preterm birth was attenuated but still increased (9.5% vs 7.2%; risk difference, 2.4%; 95% CI, 1.1-3.6%; P < 0.001).
COMMENTARY
Obesity in pregnancy is a major problem in the United States with more than one-half of pregnant women being overweight or obese.1 We know that overweight and obese pregnant women are at higher risk of pregnancy complications including miscarriage, stillbirth, gestational diabetes, hypertensive disorders including preeclampsia, and cesarean delivery.2 One of the most effective treatments for obesity is bariatric surgery, which is presently recommended for a BMI of ≥ 40 kg/m2 or a BMI of ≥ 35 kg/m2 with significant medical comorbidities. The number of reproductive-aged women who are choosing bariatric surgery to treat their obesity is increasing.1 Whether women who undergo bariatric surgery to lose weight and then get pregnant are still at increased risk of pregnancy complications is unclear. Before this study, one meta-analysis of three cohort studies suggested that after bariatric surgery, women were at no higher risk of preterm birth or fetal growth restriction compared to the general population or obese controls.3 However, other smaller studies indicated a concern regarding nutritional levels after bariatric surgery influencing fetal growth.
Some experts recommend delaying conception for 12-24 months after bypass surgery. This is to allow the period of rapid weight loss to occur without any risk of compromising fetal growth from poor nutrition in the mother.4 Because fertility often increases after bariatric surgery, women who want to delay pregnancy need to be placed on a reliable contraceptive method. All contraceptive methods are options for women after bariatric surgery except for oral contraceptives in women who have had a malabsorptive procedure (Roux-en Y gastric bypass or biliopancreatic diversion). Depending on the type of bariatric surgery performed, women should be evaluated antenatally for vitamin and mineral deficiencies such as iron, vitamin B12, folate, vitamin D, and calcium.4 Consultation with a nutritionist and surveillance of fetal growth with ultrasound may also be indicated depending on their pre-pregnancy weight.
This Swedish study is a well-done, matched, population cohort study that took advantage of national databases to ensure a representative sample. However, this study also falls victim to the inherent limitations of observational epidemiology.5 One, the absolute risk differences are small but carry statistical significance because of the large sample size. Two, there was no relationship between the time interval of surgery to delivery and pregnancy outcomes, which does not seem to make clinical sense. One would expect worse outcomes in women who get pregnant within 1-2 years of bariatric surgery during the period of rapid weight loss. Three, the BMI level in early pregnancy influenced the results but not in the direction one would anticipate. Women with a BMI of < 35 kg/m2 had the highest risk of preterm birth, not women with a BMI ≥ 35 kg/m2. The authors don't have any explanations for these findings. Even though this study used matched controls, there can still be unmeasured confounders present that could influence the results. In addition, the authors did not have access to pre-surgery weight and degree of weight loss between surgery and pregnancy. Although this study received press attention, I don't think it definitively answers the question about the risks of pregnancy after bariatric surgery. Certainly, as clinicians we want to encourage women to have a healthy weight prior to pregnancy. Given all the factors that influence pregnancy outcomes, it will be difficult to isolate the effect of bariatric surgery itself. In the meantime, women who become pregnant after bariatric surgery should be carefully monitored for fetal growth. If the patient is still obese, it may be necessary to use ultrasound rather than fundal heights as the measurement tool.
References
- ACOG Committee Opinion Number 549. Obesity in pregnancy. Obset Gynecol 2013;121:213-217.
- Weiss JL, et al. Obesity, obstetric complications and cesarean delivery rate — a population-based screening study. Am J Obstet Gynecol 2004;190:1091-1097.
- Maggard MA, et al. Pregnancy and fertility following bariatric surgery. JAMA 2008;300:2286-2296.
- ACOG Practice Bulletin Number 105. Bariatric surgery and pregnancy. Obstet Gynecol 2009;113:1405-1413.
- Grimes DA, Schulz KF. False alarms and pseudo-epidemics: The limitations of observational epidemiology. Obstet Gynecol 2012;120:920-927.
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