The approach to a pregnancy after bariatric surgery

Abstract

With a rising worldwide incidence of obesity, particularly in the young, bariatric surgery offers an effective method of meaningful and sustained weight loss. At present, most bariatric procedures are carried out in women and increasingly in younger age groups. In line with the fertility benefits associated with weight loss, pregnancy after bariatric surgery is now a very common scenario. Although there is limited evidence to support optimal care in this group, most women appear to have good pregnancy outcomes, with reduced rates of pre-eclampsia and gestational diabetes (GDM). However, rates of stillbirth and small-for-gestational-age (SGA) babies are increased, suggesting that screening and supplementation of micronutrients is likely to be very important in this cohort. The risks and benefits that bariatric surgery may pose to pregnancy outcomes, both maternal and fetal, are largely dependent upon the degree of weight loss, weight stability upon entering pregnancy, surgical complications and the time interval between bariatric surgery and pregnancy. Ideally, preconception care would be more widely available, helping to assess and address micronutrient deficiencies and support preparation for pregnancy.

Key points:

• 1.A history of bariatric surgery is increasingly common in women of reproductive age and is associated with improved fertility and reduced incidence of pre-eclampsia and gestational diabetes in pregnancy.
• 2.However, pregnancy after bariatric surgery also carries higher risks of small-for-gestational-age (SGA) babies and stillbirth; it is unclear why these occur.
• 3.Ideally, preconception planning would encourage a delay in conception until at least 12 months post-surgery and provide an opportunity to assess and address micronutrient status.
• 4.Screening for gestational diabetes is important but challenging, since the oral glucose tolerance test (OGTT) is not recommended for most women after bariatric surgery.
• 5.Post-operative complications such as postprandial hyperinsulinaemic hypoglycaemia (dumping syndrome) may also cause additional challenges in pregnancy.

Introduction

Obesity is a global pandemic affecting nearly one billion people.¹ In 2023, 58.6% of women in the UK were obese.² Young women with obesity are at high risk of fertility problems and obesity-related metabolic complications such as prediabetes, type 2 diabetes mellitus (T2DM) and polycystic ovary syndrome. Pregnancy for these women carries a higher risk of complications ante- and postnatally. Bariatric surgery offers the most effective method of attaining sustained weight loss of ≥ 20% over 10 years and remission of obesity-related complications.³ Over the past 20 years, surgical procedures have evolved, offering personalised options with varying risks and benefits. Weight loss is achieved through restrictive or malabsorptive effects, with associated neurohormonal metabolic adaptations.³ The vast knowledge gained from bariatric surgery has advanced understanding of obesity’s complex metabolic and neurohormonal pathophysiological pathways, aiding the development of newer anti-obesity medications.

Bariatric surgery in the UK

Patients with class III obesity (BMI ≥ 40 kg/m²) or class II obesity (BMI 35–39 kg/m²) with obesity-related comorbidities qualify for bariatric surgery in the NHS.⁴ For ethnic minorities, a lower BMI threshold (reduced by 2.5 kg/m²) should be considered.⁴ In the UK and internationally, bariatric surgery is widely available privately.

In the UK, common bariatric procedures (Table 1) include the Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), with adjustable gastric banding (AGB) now less commonly used.⁵ RYGB creates a small gastric pouch (restrictive) and two anastomotic limbs, one bypassing the pylorus and duodenum draining into the jejunum and the second connecting the pouch to the other limb (malabsorptive). VSG, the most common procedure, forms a smaller ‘sleeve’ stomach (restrictive). Both procedures induce weight loss by increasing levels of glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY) and altering bile acid metabolism, while VSG reduces ghrelin.^3,6 AGB involves placing an adjustable/removable silicone ring around the stomach (restrictive) with minimal neurohormonal changes.^3,6

Table 1.

Types of bariatric surgeries.

Restrictive

Adjustable gastric banding

Vertical sleeve gastrectomy

Malabsorptive

Biliopancreatic diversion

Biliopancreatic diversion with duodenal switch

Combined procedures

One anastomosis gastric bypass (mini bypass)

Roux-en-Y gastric bypass

Single anastomosis duodenal-ileal bypass with sleeve gastrectomy

Other procedures approved by the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) include biliopancreatic diversion with duodenal switch, one anastomosis gastric bypass (mini bypass), single anastomosis duodenal-ileal bypass with sleeve gastrectomy, and biliopancreatic diversion.⁷

Review of bariatric guidelines in pregnancy

According to the IFSO global registry, 81% of bariatric surgeries worldwide are performed on women.⁷ Bariatric surgery significantly reduces maternal and fetal risks associated with obesity, including T2DM, cardiovascular disease, pregnancy-associated hypertensive disorders (eg pre-eclampsia), caesarean sections, instrumental deliveries and large-for-gestational-age (LGA) babies.⁸ Women of childbearing age require preconception and nutritional counselling post-bariatric surgery.⁹ Rapid weight loss after bariatric surgery improves fertility rates by resuming ovulation, making periods more regular and alleviating features of polycystic ovary syndrome. However, bariatric surgery carries risks of complications such as malabsorption, dumping syndrome, surgical complications and nutrient deficiencies.¹⁰ Restrictive surgical procedures may have better perinatal outcomes, fewer postoperative complications and nutritional deficits compared to malabsorptive procedures, though further research is needed.^8,10

Pregnancy shortly after bariatric surgery is linked to micro- and macronutrient deficiencies, increasing the risk of prematurity, small-for-gestational-age (SGA) babies, intrauterine growth restriction, neural tube defects and increased neonatal intensive care admissions.⁸ Hence, women are advised to wait 12–24 months post-surgery before planning pregnancy to ensure weight stability, metabolic homeostasis and management of complications, thereby optimising outcomes for mother and child.⁹

In 2017, a multidisciplinary meeting of international experts established consensus guidelines (Table 2) for pregnancy after bariatric surgery.⁹ These guidelines covered contraception, nutritional advice, surgical complications, postprandial dumping syndrome, mental health, diabetes screening and ultrasound monitoring during pregnancy. Regardless, considerable knowledge gaps remain, underscoring the need for further research in this area.

Table 2.

Guidelines for pregnancy after bariatric surgery.

Guideline	Recommendation
Timing to pregnancy	1) 12–24 months post-surgery, after adequate counselling of nutrient supplementation, weight maintenance methods during pregnancy and recognition of possible complications.
Contraception	1) Women should be counselled on the importance of effective contraception, even if previously having difficulty conceiving. 2) Oral contraceptive pills are not effective due to gastrointestinal anatomical changes post-surgery leading to malabsorption, vomiting and diarrhoea. 3) Long-acting reversible contraception such as copper intrauterine device, intrauterine systems and progestogen implants do not appear to be affected by bariatric surgery. 4) Barrier methods (male condoms) can also be used; however, female diaphragms are less reliable due to the frequent size change with rapid weight loss.
Surgical complications	1) Women should be counselled on the risks of surgical complications, especially with RYGB (internal herniation) and AGB (band slipping). 2) Increased risk of preterm delivery, as severe abdominal pain may trigger uterine contractions. 3) The most common presenting feature is abdominal pain – this should be taken seriously. It is important to rule out possible abdominal obstruction due to internal herniation, which may recur several times during the same pregnancy.
Postprandial dumping syndrome	1) Early (60 min post-food; ‘early dumping’) – most common, leading to symptoms of dizziness, flushing and palpitation. 2) Late postprandial symptomatic hypoglycaemia (60–180 min post-food; ‘late dumping’) – less common. Evidenced by Whipple’s triad: a. Neuroglycopenic symptoms (anxiety, sweating, confusion) b. Biochemical evidence of hypoglycaemia c. Resolution of symptoms on ingestions of carbohydrates 3) Nutritional advice is helpful in avoiding or limiting these effects. a. Early: Avoid rapidly absorbed carbohydrates b. Late: Low glycaemic index carbohydrates, mixing carbohydrates with protein, small frequent meals and may need medical management.
Nutritional monitoring and supplementation	1) Monitor FBC, haematinics, micronutrients, liver and kidney function 2) Multivitamins, minerals and folic acid supplementation advised pre-, during and post-pregnancy
Diabetes screening	1) Women planning pregnancy should be screened for T2DM by fasting plasma glucose or HbA1c levels. 2) OGTT is not recommended, as it may precipitate dumping syndrome and results are not validated. 3) Women should be screened in pregnancy for gestational diabetes – typically with self-monitoring of blood glucose. 4) Continuous glucose monitoring may be useful.
Mental health screening	1) Should be done regularly before and after conception. 2) Screen for anxiety, depression and substance abuse.
Breastfeeding	1) Recommended with continuous monitoring of micronutrients during pregnancy. 2) Multivitamins are recommended with nutritional advice.

Adapted from Shawe et al.⁹

Nutritional deficiencies and management

All bariatric surgeries carry a risk of nutritional deficiencies, with a lower risk in restrictive procedures like AGB and gastric sleeve, and a higher risk in more malabsorptive surgeries such as gastric bypass, duodenal switch and older procedures. Thus, specialist dietitian input is essential from preconception to postpartum. Dietitians assist with weight management, promote a healthy balanced diet and optimise micronutrient supplementation to ensure woman and fetal health.^9,11,12 Unfortunately, there is limited evidence on the optimal diet, ideal nutritional monitoring and supplementation for this population. Consequently, guidance relies on a combination of dietary advice given post-surgery and during pregnancy.⁹

Weight

Weight stability should be achieved preconception and weight monitored throughout pregnancy to prevent complications from insufficient or excessive weight gain. In the absence of specific weight targets for women post-surgery, the Institute of Medicine¹³ recommendations for pregnant women are followed. Insufficient gestational weight gain requires close fetal growth monitoring and management of under-nutrition based on local nutrition protocols. Excessive gestational weight gain requires limiting energy-dense foods. In women with AGB, adjustments are made according to the gestational weight gain and fetal growth.^9,11 Importantly, long-term weight loss from bariatric surgery is not impacted by pregnancy, but post-birth weight management support remains crucial.⁹

Healthy balanced diet

A healthy, balanced diet post-surgery involves different food group choices and smaller meal portions with emphasis on lean protein, followed by vegetables and low glycaemic index starchy carbohydrates.⁹ High glycaemic index foods should be avoided to reduce the risk of dumping syndrome. Energy and protein requirements are tailored to individual pre-pregnancy BMI, gestational weight gain and physical activity, with a minimum of 60 g per day of protein recommended for all.¹³

Micronutrient deficiencies are reported in pregnant women after bariatric surgery, but evidence on neonatal outcomes is inconclusive.¹² Therefore, increased nutritional monitoring (Table 3) in each trimester and appropriate supplementation are advised.^9,12 There is insufficient evidence regarding the optimal nutritional monitoring and interpretation of micronutrient profiles following bariatric surgery. During pregnancy, it is important to use pregnancy-specific reference ranges. In most cases, supplementation with a complete multivitamin and mineral formula should be adequate, containing at least the following amounts: copper (2 mg), zinc (15 mg), selenium (50 µg), folic acid (5 mg), iron (45–60 mg or >18 mg after after AGB), thiamine (>12 mg), vitamin E (15 mg), vitamin K (90 µg), and beta-carotene (vitamin A, 5,000 IU).¹⁴ Additionally, managing nausea and vomiting, common in the first trimester, is crucial as these can worsen deficiencies, alongside addressing dumping syndrome and gestational diabetes, all requiring careful dietary management and support.⁹

Table 3.

Guidance on screening and supplementation of micronutrients.^9,11,12

Guideline	Recommendation
Blood tests (related to nutritional deficiencies)	1) Blood tests to be repeated every trimester should include: haematinics, calcium, vitamin D, phosphate, PTH, magnesium, vitamin A 2) Monitor vitamin E, zinc, copper and selenium in the first trimester 3) Vitamin K and E levels in women who had long-limb bypass or BPD/DS surgeries
Multivitamin	1) After all bariatric surgery procedures, a daily complete multivitamin and mineral supplement needs to be taken, which needs to continue throughout preconception and pregnancy and should include:  a. thiamine, iron, zinc, copper and selenium, folic acid, thiamine, vitamin B12, vitamin D, vitamin E and vitamin A in the form beta-carotene.  b. pregnancy-specific micronutrient supplements are needed in pregnancy.
Vitamin A	1) Vitamin A in the form of retinol needs to be avoided during pregnancy, due to its teratogenicity risk. 2) Replace this with beta-carotene, included within the multivitamin.
Folic acid	1) Women should start 0.4 mg folic acid preconception and throughout the first trimester to reduce the risk of neural tube defects. 2) Women who have a BMI of >30 kg/m2 or with pre-existing diabetes will need 5 mg folic acid.
Thiamine and vitamin B	1) If there is prolonged vomiting, there is risk of thiamine deficiency. 2) Prescribe 200–300 mg thiamine with vitamin B complex. 3) Intravenous replacement may be needed in severe cases, typically in the form of Pabrinex.

All other micronutrients need to be monitored and supplemented according to need.

Gestational diabetes screening

Although the risk for developing T2DM and gestational diabetes is reduced in women after bariatric surgery, it remains higher than in women post-bariatric surgery compared with the general population.¹⁵ Screening for GDM is typically done at 24–28 weeks, but women with a history of GDM, suspected undiagnosed or pre-existing T2DM may be tested at booking or earlier with fasting glucose or HbA_1c to rule out overt diabetes. Post-bariatric surgery, altered glucose transit through the gut leads to common but short-lived postprandial glucose spikes. The definition of hyperglycaemia in pregnancy in the context of bariatric surgery has yet to be clearly defined.

OGTT are often poorly tolerated by women who have undergone procedures like RYGB, VSG and BPD/DS as these can trigger dumping syndrome.¹⁶ The HbA_1c test has limited accuracy during pregnancy, and a more sensitive test should be employed to identify women with GDM.¹⁷ For these women, two alternative strategies have been proposed; home monitoring of fasting, pre-meal and 1 or 2 h postprandial blood sugars for 1 week is appropriate between 24 and 28 weeks.¹⁸ Similar to recommendations for women with a previous history of GDM, capillary blood glucose monitoring may begin early at 14–16 weeks and continue throughout pregnancy.¹⁹ Glucose targets for gestational diabetes are <5.3 mmol/L fasting, <7.8 mmol/L 1 h, and <6.4 mmol/L 2 h post-meal. Persistent glucose elevations warrant treatment. Dumping syndrome is less common in women with purely restrictive procedures like AGB,²⁰ allowing them to follow standard GDM testing guidelines. If diet and lifestyle intervention are inadequate, pharmacotherapy is indicated. Malabsorptive procedures may impact the absorption of oral hypoglycaemic agents like metformin,²¹ but, if necessary, rapid release formulations are preferred over modified-release ones. Insulin can be used, but careful risk–benefit assessment is necessary due to the risk of hyperinsulinaemic hypoglycaemia, which is difficult to treat. High glycaemic index foods may worsen or perpetuate hypoglycaemia. Given the low rates of pre-eclampsia and LGA babies in this population, the benefits of pharmacological treatment of mild hyperglycaemia are unclear.

Pregnancy outcomes (Table 4)

Table 4.

Implications of bariatric surgery on pregnancy outcomes.

Benefits	Disadvantages
Excessive gestational weight gain ↓	Inadequate gestational weight gain ↑
Pre-eclampsia ↓	Anaemia ↑
Gestational diabetes ↓	Surgical complications ↑
Pregnancy-related hypertensive disorders↓	Anxiety and depression ↑
LGA baby↓	SGA baby ↑

LGA, large-for-gestational-age baby; SGA, small-for-gestational-age baby; ↓, reduced frequency; ↑, increased frequency.

Fetal outcomes

Fetal growth monitoring should occur monthly from viability, with increased frequency if insufficient gestational weight gain. In practice, monthly fetal growth monitoring often commences in the third trimester, as scans performed later in pregnancy are more reliable for predicting growth deviations.²² Inadequate maternal weight gain is associated with lower birth weight, lower gestational age, and higher rates of very preterm births. This is more frequent in pregnancies occurring less than 12 months after bariatric surgery,²³ reported in 75% of such cases.⁶ Data suggest a trend towards increased frequency of SGA babies following bariatric surgery, relative to BMI-matched controls,²⁴ with a reported SGA baby prevalence of 23%, which is more than twice that expected (<10th centile).²³ Highest SGA baby incidence is in pregnancies less than 12 months after bariatric surgery (31%).²³ AGB deflation is recommended if fetal growth is compromised.⁹ A reduction in macrosomia (>90th centile) is reported after AGB, in comparison to women with obesity⁹ despite lower mean gestational weight gain. LGA occurred in 21% of pregnancies post-AGB, relative to 5% post-VSG/RYGB. Preterm birth was higher (13%) with AGB, relative to VSG/RYGB (8%).²⁵

Maternal outcomes

Pregnancy following bariatric surgery is linked to lower gestational weight gain,⁹ reduced pre-eclampsia and GDM.¹⁵ Monitoring for GDM should occur as previously outlined. AGB is associated with the lowest postoperative GDM risk (7%).²⁵ RYGB presents the greatest risk of surgical complications during pregnancy,²⁵ with internal herniation occurring in 8%, typically presenting with abdominal pain.⁹ Risk of gastric band slippage is 12%, relative to 3–5% outside pregnancy, and commonly presenting with vomiting.²⁶ Deflation can mitigate this risk.⁹ Anaemia during pregnancy is more common after bariatric surgery,¹⁵ particularly after RYGB (39%), and less frequent after AGB (16%).²⁵ Bariatric surgery is associated with a higher prevalence of mental health disorders and substance abuse, necessitating screening during pregnancy.⁹

Postpartum care

Pregnancy does not affect long-term maternal weight after bariatric surgery.⁹ Breastmilk is not compromised after bariatric surgery, but maternal micronutrient monitoring during lactation is recommended.⁹

Conclusion

As bariatric surgery becomes more common for treating obesity, many young women with severe obesity will experience a pregnancy after bariatric surgery. To ensure a healthy pregnancy post-surgery, women should be advised to delay pregnancy until they achieve weight stabilisation, nutritional optimisation, and are taking regular micronutrient supplementation. Managing pre-existing obesity-related complications such as hypertension, diabetes and mental health issues is also crucial. During pregnancy, screening for gestational diabetes, monitoring for dumping syndrome and watching for surgical complications like internal herniation and band slippage are important. Additionally, postnatal support for breastfeeding should be provided.

CRediT authorship contribution statement

Harriet D Morgan: Writing – review & editing, Writing – original draft, Project administration, Conceptualization. Amy E Morrison: Writing – original draft. Malak Hamza: Writing – original draft. Cathy Jones: Writing – original draft. Caroline Borg Cassar: Writing – original draft. Claire L Meek: Writing – review & editing, Supervision, Conceptualization.

Declaration of Competing Interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.