Globally, an estimated one in five women aged 20 years or older is obese, defined as a body mass index (BMI) ≥30 kg/m2 (Ng et al, 2014). It is becoming increasingly common for pregnant women to have undergone bariatric surgery before conceiving. Bariatric surgery has been associated with a decreased risk of gestational diabetes and excessive fetal growth; shorter gestation, and an increased risk of small-for-gestationalage fetuses (Johansson et al, 2015). Gestational diabetes mellitus (GDM) is defined as the onset of glucose intolerance in pregnancy and is increasing in prevalence due to a number of factors, including the rising incidence of obesity (Catalano and Shankar, 2017). In the UK, GDM affects between 3% and 5% of all pregnancies (Ryan et al, 2018). GDM is now recognised as one of the most common complications of pregnancy, and has increased by more than 30% worldwide within the past 20 years (Zhu and Zhang, 2016). Gestational diabetes can lead to adverse maternal and fetal outcomes and it is therefore important that GDM is diagnosed and managed appropriately in pregnancy (Monteiro et al, 2016). The World Health Organization (WHO) (2016) recommends diagnosing GDM if any of the following criteria are met:
However, the WHO criteria for diagnosing diabetes is not used within the UK, and instead Diabetes UK (2018) recommends:
In many clinical environments, the diagnosis of GDM involves taking a woman's fasting blood glucose level, and then asking her to consume a 75g glucose drink over a 5-minute period. The woman is then required to remain sedentary and further blood glucose levels are taken at 1 and 2 hours after ingestion of the glucose drink (WHO, 2016). Some women have reported side effects from the oral glucose tolerance test (OGTT) in the form of sweating, headaches, light-headedness and stomach pain (American Diabetes Association, 2015). These are commonly caused by hypoglycaemia and often subside after the test is completed; however, if a woman has history of sleeve gastrectomy, she may not be able to undertake the OGTT, due to the risk of dumping syndrome. Dumping syndrome, or rapid gastric emptying, occurs when foods, particularly those high in sugar, pass rapidly from the stomach to the duodenum. It causes an initial rise in blood glucose level and a rapid increase in insulin secretion, which leads to rebound hypoglycaemia, producing symptoms that may include vomiting, diarrhoea, abdominal pain, irregular heart rate and dizziness (Feichtinger et al, 2017).
There is limited research on the effects of weight loss surgery on the pregnancy OGTT, despite there being a recent increase in women of childbearing age undergoing bariatric weight loss surgery (Carreau et al, 2017). This has seen a review of obstetric guidelines in relation to diagnostic tools used for these women, particularly in relation to testing for GDM. Conducting an OGTT on a woman who has had either a Rouxen-Y gastric bypass or a sleeve gastrectomy may be an inadequate form of diagnosing GDM and may lead to further health issues for the woman and fetus, as well as poor neonatal outcomes.
A Roux-en-Y gastric bypass is a bariatric weight loss surgery that involves the creation of a small pouch from the stomach, which is then connected to the small intestine. Following this procedure, swallowed food travels through the newly created pouch of stomach and then directly into the small intestine. This procedure can increase the risk of iron deficiency anaemia, as the amount of iron-rich foods the new stomach can accommodate is greatly reduced and meat is often no longer tolerated (Salgado et al, 2014). However, no studies have revealed any adverse effects on obstetric outcomes, including intrauterine growth restriction (IUGR) of the fetus (Crusell et al, 2016).
A sleeve gastrectomy involves reducing the stomach to approximately 15% of its original size, changing it from a pouch to a thin, vertical sleeve using a stapling device. The gastric sleeve typically can accommodate between 50–150 ml and is approximately the size and shape of a banana. The prognosis of pregnancy following bariatric surgery has been deemed as good with no excess risk of congenital malformations (Dabi et al, 2017).
The most significant issue for women who have had bariatric weight loss surgery and are undertaking an OGTT is the risk of rebound hypoglycaemia. There have been several documented studies on postprandial hypoglycaemia in women who have had a gastric bypass or sleeve gastrectomy (Jiménez et al, 2015; Lee et al, 2015). A Roux-en-Y gastric bypass has the most significant links with hypoglycaemia, as the secretion of postprandial glucagon-like peptide-1 (GLP-1) leads to a hyperinsulinaemia response and causes hypoglycaemia between 1 and 3 hours post-meal (Shantavasinkul et al, 2016).
Bonis et al (2016) suggest that due to an early postmeal continuous subcutaneous interstitial glucose peak, undertaking a 75g OGTT may be a substandard diagnostic tool for GDM in women who have undergone a Roux-en-Y gastric bypass. This is because the 2-hour level will likely be below the limit for a diagnosis of GDM and will therefore rely on the 1-hour level, before the peak has occurred.
Therefore, the importance of post-surgery dietary restrictions, including the limitation of carbohydrate-rich foods and avoidance of simple sugars, supports the argument that postprandial hypoglycaemia will affect pregnant women post-bariatric surgery. Pregnant women may require personalised dietary education to fully understand the mechanisms of postprandial hypoglycaemia and the risks posed to them and the fetus if they experience frequent hypoglycaemic episodes.
If a woman feels she is unable to undertake an OGTT due to previously bariatric weight loss surgery, she may be instructed to monitor her capillary blood glucose levels. A recent study investigated the use of capillary blood glucose monitoring simultaneous to venous blood glucose monitoring during a 75g OGTT (Bhavadharini et al, 2016). The findings suggested that there was a similarity of up to 92.5% in results; therefore advocating that capillary glucose monitoring may be an effective alternative to an OGTT with venous monitoring. Capillary blood glucose monitoring is a cost-effective method of measuring glucose intolerance in pregnancy; however, it does require the woman's compliance with monitoring to remain accurate. Women may be more inclined to be compliant with the monitoring as a capillary blood draw is less invasive than a venous blood draw; although the frequency and duration of capillary blood glucose monitoring may be inconvenient and less likely to be maintained for the period required to diagnose GDM.
The complications of post-bariatric surgery hypoglycaemia in a pregnant woman include general malaise, shaking, headaches, confusion and drowsiness, with more severe complications including seizures and syncope (temporary loss of consciousness caused by a fall in blood pressure) (Lee et al, 2015). Women may also experience heart palpitations during hypoglycaemic episodes. A recent study revealed that hypoglycaemia in type 2 diabetes can trigger ventricular arrhythmias, particularly ventricular tachycardia (Pistrosch et al, 2015). This has the potential to increase morbidity to pregnant women, particularly if they have pre-existing cardiac conditions that may have been triggered by obesity.
Fetal risks of maternal hypoglycaemia are generally associated with intrauterine growth restriction (IUGR). Complications related to IUGR are the leading cause of perinatal mortality with no congenital abnormalities (Nolan and Kent, 2014). IUGR will most often lead to the neonate being born small for gestational age, and more likely to experience morbidity in the form of breathing difficulties, including asphyxia, hypothermia and hypoglycaemia (Melamed et al, 2016). There is also the potential for fetal morbidity and mortality due to maternal risks such as seizures, syncope or mechanical injury leading to oxygen deprivation or placental abruption.
Whyte et al (2016) recruited 120 midwives specialising in providing care for women with diabetes, based in 164 obstetric units to analyse their practice on diagnosing GDM in women who had a history of bariatric surgery. Midwives stated that their workplaces had policies in place specific to women who had a history of weight loss surgery, and the majority said they regularly performed an OGTT as per hospital screening procedures. This suggests that clinical trials need to be implemented to address the effectiveness of the OGTT in women with a history of bariatric surgery, and will assist in developing universal guidelines for the management of post bariatric surgery pregnant women. When managing these women, it is important to include a multidisciplinary team approach, including guidance from a dietician, where screening for gestational diabetes and evaluating any gastrointestinal complaints is a focus of care provided (Kominiarek, 2011).
This article has focused on early pregnancy testing for GDM; however, GDM is a risk throughout pregnancy, especially in the second and third trimesters,. Testing is therefore required at intervals; not only when pregnancy is confirmed. Preconception counselling may also be useful for women who have undergone bariatric weight loss surgery. Obesity is a contemporary issue in maternity environments, and has led to increased exposure to pregnant women who have undergone bariatric weight loss surgery. Complications of GDM have the potential to cause severe morbidity and mortality to the woman, fetus, and neonate; therefore, it is important that women continue to be screened. The OGTT may not be well tolerated by these women and alternative guidelines need to be developed on how to accurately diagnose and manage GDM in this cohort. The incidence of postprandial hypoglycaemia can have negative consequences for the woman and neonate, including IUGR, seizures, syncope and mechanical injury in relation to these. A cost-effective alternative to the OGTT is to monitor pre-and post-meal blood glucose levels; however, more research is required to determine the period, duration and effectiveness of this method. BJM