Obesity, defined as a body mass index (BMI) of 30 kg/m² or greater, is a growing epidemic. In the United States, 35% of adults and 17% of children are obese.¹ Obesity is associated with multiple medical morbidities, including type 2 diabetes mellitus, hypertension, heart disease, stroke, cancers, and obstructive sleep apnea. Obese women are at higher risk of adverse pregnancy outcomes when compared to women with a normal BMI.² Complications in pregnancy include gestational diabetes, gestational hypertension, preeclampsia, macrosomia, fetal anomalies, and need for cesarean section.

Weight loss can reduce the risks and complications of these medical conditions. Unfortunately, behavioral modifications and medical management prove to be unsuccessful in many individuals. Surgical therapy performed to manage obesity is the only effective and proven therapy for patients with severe obesity (BMI ≥ 35 kg/m²).³

Bariatric operations are some of the most commonly performed surgeries. In 2011, over 340,000 bariatric procedures were performed worldwide, with more than 120,000 procedures performed in North America.⁴ The majority of these surgeries are performed in reproductive-aged women.⁵ In addition, the use of bariatric surgery in the adolescent population is rising.⁶ This poses significant implications for women prior to and during pregnancy. Clinicians caring for reproductive-aged women need to be familiar with the various types of bariatric surgeries, the recommendations for management in pregnancy, and the associated complications and risks to both the patient and her fetus.

Current indications for bariatric surgery include a BMI of 40 kg/m² or greater or a BMI of 35 kg/m² or greater with comorbid medical conditions.⁷ Individuals meeting criteria should also have attempted and failed other weight loss treatments. In addition, patients are expected to be psychologically stable.

Weight loss from bariatric surgery occurs through two general mechanisms: restriction of intake or malabsorption of ingested food. Procedures may have a combination of both malabsorptive and restrictive components. The Roux-en-Y gastric bypass, which is a mixed malabsorptive-restrictive surgery, is the most commonly performed surgery for weight loss in the United States. It involves creation of a small gastric pouch that is directly connected to a portion of the jejunum known as the “Roux limb,” thereby bypassing the rest of the stomach and duodenum. The Roux limb is then linked to the remaining segment of intestine in a Y-shaped enteroenterostomy. The adjustable gastric band is another common procedure that is entirely restrictive in nature. It involves placement of a fluid-filled band around the fundus of the stomach, reducing its functional volume. Depending on the type of procedure performed, patients may be at risk for micronutrient deficiencies, decreased absorption of medications, dumping syndrome, and gastric ulcers. It is important for medical providers to consider these potential complications in pregnant women with a history of bariatric surgery.

Weight loss after bariatric surgery can restore the normal hormonal milieu, thereby improving ovulatory dysfunction and infertility.^8,9,10,11 It is important to counsel women on the improvement in fertility and to discuss options for contraception. Due to the malabsorptive nature of some of the surgical procedures, there is an increased risk of oral contraceptive failure.¹² Alternative nonoral forms of hormonal contraception should therefore be considered.¹⁰ Despite improved fertility rates after weight loss, bariatric surgery should not be used as a primary treatment for infertility.

The current recommendation is for women to wait 12–18 months after bariatric surgery prior to pursuing pregnancy. This is due to the potential concern that rapid postoperative weight loss and subsequent nutrient deficiencies may result in adverse effects on the pregnancy.¹³ Although the recommendation is to delay conception for at least 12 months following bariatric surgery, data suggest that pregnancy outcomes tend to be favorable among patients who conceive within 1 year. Observational studies did not note any significant differences in obstetric and neonatal complications, including fetal growth restriction, preterm delivery, preterm premature rupture of membranes, preeclampsia, gestational diabetes, cesarean delivery, or congenital anomalies, among postsurgical patients conceiving prior to or after the 12- to 18-month window.¹⁴ Limited data also suggest that the length of time to conception following surgery does not affect total postoperative weight loss.¹⁵

Weight loss in obese women prior to pregnancy generally results in more favorable outcomes for both the mother and the neonate.¹⁶ Despite bariatric surgery, most women remain obese at the start of pregnancy.¹⁷ Interpreting pregnancy outcomes in women after bariatric surgery can be challenging due to the different control groups, which include obese women without bariatric surgery, the same women prior to their bariatric surgery, or the general obstetric population. In general, pregnancy outcomes in women following bariatric surgery are more favorable than when compared to obese women who have not undergone a weight loss procedure.

Bariatric surgery leads to higher rates of diabetes remission when compared to other weight loss methods.¹⁸ The return to normal blood glucose levels and discontinuation of diabetes-related medications occurs soon after surgery.^19,20 Pregnancy outcomes are improved as these women enter pregnancy in a euglycemic state and avoid the pregnancy complications associated with pregestational diabetes.²¹ Observational studies have also demonstrated a reduction in the incidence of gestational diabetes mellitus among pregnant women who have undergone bariatric surgery.^22,23,24 Although the risk of gestational diabetes in these women is lower than in obese women who have not had surgery, the risk is still higher than the baseline risk.^25,26,27 Studies comparing pre– and post–bariatric procedure pregnancy outcomes also demonstrated a significant reduction in the risk of gestational diabetes.^28,29 Outside pregnancy, the most common procedures, including gastric bypass, sleeve gastrectomy, and gastric banding, all lead to an improvement in diabetes.³⁰ It is not certain if the type of surgical procedure affects the rate and outcome of gestational diabetes in pregnancy.

In addition to diabetes, bariatric surgery improves other cardiovascular risk factors, such as hypertension and dyslipidemia.³¹ These women are at lower risk for developing hypertensive complications in a future pregnancy. Observational studies have demonstrated that the incidence of preeclampsia is reduced in women after weight loss surgery when compared to both obese women and pregnancies in the same women prior to bariatric surgery.^23,26,32

Obesity is a definite risk factor for cesarean section, with the magnitude of risk correlated to the degree of obesity.³³ The risk of cesarean section persists in patients post–bariatric surgery, the majority of whom remain obese after surgery, when compared to nonobese pregnant patients.^25,34 Cesarean section rates are not higher in pregnant women after bariatric surgery than in their obese nonsurgical counterparts.^34,35

Medically indicated preterm deliveries are more common among obese women due to obesity-related comorbidities, such as hypertension and diabetes.³⁶ Pregnancy after bariatric surgery is associated with a reduction in these iatrogenic preterm births.²³ The association between obesity and spontaneous preterm deliveries is less clear. Earlier studies demonstrated that obesity is not associated with an increased risk of spontaneous preterm birth,³⁶ but more recent, larger studies suggested that the risk is increased, particularly for preterm deliveries prior to 28 weeks.³⁷ The data regarding preterm delivery after bariatric surgery are also mixed. Prior studies did not show an increased risk of postsurgical preterm birth,^17,25 although a more recent, larger study found that women after bariatric surgery are at higher risk of both indicated and spontaneous preterm deliveries.³⁸

Maternal obesity is a significant risk factor for macrosomia, infants who are large for gestational age, and later offspring obesity.³⁹ The risk is greatest for women with class III obesity (BMI ≥ 40 kg/m²).⁴⁰ Pregnancies following bariatric surgery result in lower mean birth weights and a reduction in the incidence of macrosomia.^22,23,26 Meanwhile, postsurgical infants have also been shown to have an increased risk of being born small for gestational age (SGA) when compared to babies born to both nonobese and obese women.^{22,24,27,38,41} The risk for SGA may be highest with malabsorptive procedures, including gastric bypass.³⁵