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Pregnancy following Gastric Bypass Surgery Study Protocol

Key points

  • Obesity is associated with significant maternal and fetal complications during pregnancy and birth.
  • Gastric bypass surgery is being increasingly undertaken by women of reproductive age, resulting in increased numbers of pregnancies following gastric bypass surgery.
  • Guidelines for optimal management of pregnancy following gastric bypass surgery have not yet been established.

Surveillance Period

1st April 2014 – 31st March 2016


The prevalence of maternal obesity is dramatically rising in the UK, with approximately 5% of women having a BMI of 35 or over at any point in pregnancy. The adverse consequences of obesity on maternal and perinatal health are well established1.

Gastric bypass surgery is an effective procedure used to achieve weight loss in people with morbid obesity. The most commonly performed surgery is a Roux-en-Y gastric bypass, which can be an open or laparoscopic procedure. It involves creating a small pouch from the stomach and reconnecting this to a section of the small intestine, bypassing the larger, remaining stomach. These anatomic changes reduce food intake and absorption, thereby inducing weight loss. The increase in gastric bypass surgery amongst women of reproductive age has resulted in an increasing number of pregnancies following bypass surgery.

Several studies and reviews2, 3, 4 have analysed pregnancy outcomes following bariatric surgery. Studies demonstrate a reduction in obesity-related gestational complications such as gestational diabetes and maternal hypertension. There appear to be conflicting results regarding the incidence of intrauterine growth restriction and mode of delivery following bariatric surgery3, 4, 5, 6. Complications such as intestinal hernias, nutritional deficiencies4, 5 and increase in birth defects6 in pregnancies following gastric bypass surgery have also been cited. Studies conducted thus far emphasise the importance of appropriate monitoring and effective nutritional control, although this is not currently defined.

There is a need for robust evidence regarding how long to delay pregnancy following bariatric surgery. Due to the potential nutritional deficiencies and concomitant complications associated with rapid weight loss, current advice is to delay pregnancy for 1 year after bypass surgery2, 7. However, studies have shown similar maternal and neonatal outcomes between patients who conceived during the first post-operative year, and those who conceived after2, 8.


To use the UK Obstetric Surveillance System (UKOSS) to describe the epidemiology, management and outcomes of pregnancy following gastric bypass surgery in the UK and to assess current practice and develop further guidelines for optimal management.

Research questions

  • What is the current incidence of previous gastric bypass surgery in pregnancy in the UK?
  • What is current practice with regards the management of pregnant women following gastric bypass?
  • Is gastric bypass surgery associated with any adverse maternal or fetal complications?
  • What is the incidence of obesity-related gestational complications following gastric bypass surgery?
  • Are there differences in outcomes with time period between bypass surgery and becoming pregnancy (more than/less than one year)?

Case definition

Any woman with a confirmed ongoing pregnancy following gastric bypass surgery. Please include all types of surgery (Roux-en-Y, Duodenal switch, Gastric sleeve or other).
Exclude: Any woman who had a gastric band.


This study is funded by North Bristol NHS Trust.

Ethics committee approval

This study has been approved by the NRES Committee London – City Road & Hampstead
(study reference 14/LO/0491).

Lead Investigator

Katie Cornthwaite, Dimitrios Siassakos, Judith Hyde, Tim Draycott, Andrew Johnson, Southmead Hospital, Bristol


  1. ^ Usha Kiran, T.S., et al., Outcome of pregnancy in a woman with an increased body mass index. BJOG, 2005. 112(6): p768-72
  2. ^ a, b, c National Obesity Observatory. Bariatric surgery for obesity: Department of Health; 2010. Available at
  3. ^ a, b Josefsson A, Blomberg M, Bladh M, et al. Bariatric surgery in a national cohort of women: sociodeomgraphics and obstetric outcomes. Am J Obstet Gynecol 2011; 205:206.el-8
  4. ^ a, b, c Guelinckx I, Devlieger R, Vansant G. Reproductive outcome after bariatric surgery: a critical review. Hum Reprod Update 2009; 15: 189-201
  5. ^ a, b Kjaer MM, Lauenborg J, Breum BM, et al. The risk of adverse pregnancy outcome after bariatric surgeryL a nationwide register-based matched cohort study. Am J Obstet Gynecol 2013; 208: x-ex-x-ex
  6. ^ a, b Kjaer MM, Nilas L. Pregnancy after bariatric surgery – a review of beefits and risks. Acta Obstet gynecol Scand 2013; 92:264-271
  7. ^ Dalfra MG et al. Prengancy and foetal outcome after bariatirc surgery: a review of recent studies. Journal of Mternal-Fetal and Neonatal Medicien, 2012;25(9): 1537-1543
  8. ^ Sheiner E, Edri A, Balaban E, et al. Pregnancy outcome of patient who conceive during or after the first year following bariatric surgery. Amn J Obstet Gynecol 2011; 204:50.el-6

Updated: Friday, 09 October 2020 10:27 (v6)