Gestational Diabetes

Gestational diabetes mellitus (GDM) is a pregnancy complication defined as impaired blood sugar regulation beginning in pregnancy, and is no longer present after delivery. Although prevalence varies, a recent study by the CDC reports that as many as 9.2% of pregnancies are affected by gestational diabetes.^[1] Symptoms of gestational diabetes are similar to that of type 2 diabetes and include polydipsia (excessive thirst), polyuria (excessive urination), hunger and fatigue.^[2] However, the majority of cases of gestational diabetes are discovered through routine prenatal screening performed between week 24 and 28 of pregnancy.^[2] Milder degrees of impaired glucose tolerance (IGT) which do not meet diagnostic criteria for GDM are also important to identify, as they may predispose to similar risks.

Risk factors for developing GDM include having gestational diabetes in a previous pregnancy, obesity (body mass index greater than 30 kg/m2), a previous baby weighing more than 4.5kg, race (Asian, Middle-eastern, and African-American), and having a first degree relative with diabetes.^[3] Additionally, new research is showing that many women who develop GDM seem have altered glucose metabolism prior to conception, which is unmasked later in pregnancy.^[4] Gestational diabetes is important to identify and manage due to the potential for complications during pregnancy and neonatal outcomes, as well as long term health risks for both the mother and offspring. For the mother, GDM predisposes to increased risk of pre-eclampsia (and therefore seizure and stroke during labour and delivery), need for caesarian section, and developing type 2 diabetes later in life.^[3] For the baby, risks include macrosomia (large birth weight), hypoglycemia after birth, and increased risk of obesity and glucose intolerance later in life.^[5] Once diagnosed, typical treatment plans vary depending on the severity of the condition. Blood glucose levels are carefully monitored while fasting and 1 and 2 hours after a meal (postprandial). Hemoglobin A1C may also be monitored in some cases, and is a long-term measurement of glucose control over the past 3 months. Nutrition and lifestyle factors are inarguably the cornerstone of treatment and may often be sufficient to manage GDM, however research and specific recommendations are limited. This article aims to identify specifics diet and lifestyle factors to prevent and treat gestational diabetes mellitus.

DIET

Studies investigating various diets and specific recommendations for gestational diabetes are conflicting, and often so too are recommendations from a woman’s healthcare providers. Although experts agree a generally ‘healthy’ diet is beneficial in GDM, what exactly this entails is controversial, and diet requirements for maintaining blood glucose may vary between women. Due to the fluid and individualized nature of pregnancy as well as progression of GDM, it is important to continually re-evaluate blood glucose levels and efficacy of specific dietary measures in each individual person. A recent study investigated the incidence of gestational diabetes in association with adherence to the Mediterranean diet, which emphasizes whole vegetables and fruits, beans and legumes, fibre, and healthy fats such as olive oil.^[6] It was found that women who had higher adherence to a Mediterranean diet had a 38% lower incidence of gestational diabetes than those with poor adherence. Although this is an important study and provides guidance, specific recommendations are still lacking. Dietary protein is an important element to regulating blood glucose levels, especially in those with impaired glucose tolerance, however very few studies are available that focus on specific types of protein in association with GDM. A large prospective study of prepregnancy dietary protein intake was conducted to determine the strength of the association between protein intake and GDM, particularly type of protein consumed.^[4] It was found that higher consumption of animal protein prepregnancy, especially red meat, was associated with a significantly greater risk of GDM later in pregnancy. Conversely, those with higher intakes of vegetable proteins, particularly nuts, had significantly lower risk of GDM. They concluded that replacing one serving of red meat protein for an alternate healthy protein was significantly associated with reduced risk of GDM (29% for poultry, 33% for legumes, and 51% for nuts).

Research on dietary fat consumption has been controversial, mainly due to many studies investigating effects of total fat consumption, while not differentiating types of fats. In those that have made the important distinction, higher consumption of foods containing polyunsaturated fats, what most people know as ‘good fats’ such as nuts and seeds, olive oil, and fish, have been shown to reduce risk of GDM.^[7] Meanwhile, foods containing saturated fats, or ‘bad fats’ such as fatty cuts of meat, dairy, butter impairs glucose tolerance and is linked to the development of GDM. This has been shown to be true even when total fat intake is equal, indicating that it is the quality of fat, not quantity that is most important. Fibre is also an important component to managing any type of diabetes, and GDM is no different. Sources of fibre include fruits and vegetables, legumes, and whole grains such as brown rice and quinoa, and it is recommended to aim for about 30 grams of fibre per day. High fiber consumption prior to pregnancy is significantly associated with reduced risk of GDM development.^[8] In fact, it has been shown that each 5g/day increase in fruit fiber (about the amount in one medium sized apple with skin) leads to a 26% decreased risk of GDM. 

EXERCISE

It is well known that physical activity is of great importance in treatment of all types of impaired glucose regulation, however pregnancy presents a unique challenge for specific recommendations regarding previous activity level, type of exercise, and safety. The American College of Obstetricians and Gynecologists currently recommends 30 minutes of moderate-vigorous exercise, 5 times per week for healthy, pregnancy women, including both aerobic exercise and resistance training.^[9] Women who were previously sedentary are recommended to gradually work up to such guidelines. These recommendations are for uncomplicated, healthy pregnancies, and guidelines specifically for those with gestational diabetes have not been established. A controlled study to assess overall effect of maternal physical activity in pregnancy was conducted beginning at 6 to 8 weeks gestation.^[10] The exercise intervention consisted of 30 minutes of aerobic exercise performed at moderate intensity, plus warm and cool down, 3 times per week. The control group did not participate in regular physical activity. Frequency of developing GDM in the exercise group was 1.8%, vs 8.3% in the group with no physical activity, a statistically significant difference. Additionally, risk of macrosomia, a significant complication of GDM was measured to be reduced by half the exercise group vs the control group. In a recent randomized trial, women with GDM were instructed simply to perform 20 minutes of brisk walking per day.^[11] When compared to women who did not exercise daily, this simple exercise program resulted in significant reductions in postprandial blood glucose, HbA1c, and even other factors such as triglycerides. This study demonstrates that although specific guidelines and recommendations have yet to be established, a very simple, easy to follow exercise program can yield significant results.

OTHER LIFESTYLE FACTORS

Other lifestyle factors important in GDM include body weight prior to pregnancy measure by Body Mass Index (BMI), and smoking during pregnancy. To study the combined effect of a number of modifiable risk factors, a large study published in 2014 measured four factors and their relation to gestational diabetes.^[12] Risk factors studied included body weight, healthy diet, regular exercise, and not smoking. Healthy body weight prior to pregnancy was classified as BMI <25, which is generally recommended for all individuals for optimal health. Healthy diet was measured using the Alternate Healthy Eating Index which takes into account 12 components of healthy diet such as fruit and vegetable intake, total and saturated fasts, as well as variety in diet.^[13] Regular exercise was defined as 30 minutes of moderate to vigorous exercise per day, 5 days of the week. All factors were significantly and independently associated with a reduced risk of development of gestational diabetes. Being a non-smoker, engaging in healthy eating, and participating in required physical activity produced a 41% lower risk of gestational diabetes compared to other pregnancies. However when all four favourable risk factors were combined (adding healthy body weight), an even greater protection against GDM was observed, more than 80% reduced incidence of gestational diabetes, compared to those who adhered to none. While it’s clear that more research is needed concerning diet and lifestyle with respect to gestational diabetes, there are a number of recommendations that yield significant results both for prevention and management of the condition. Eating a generally Mediterranean-type diet that is high in vegetables and fruit, vegetarian protein and fish, fibre, and healthy fats significantly reduces the risk of developing GDM, and improves the condition once diagnosed. Any type of exercise during pregnancy is beneficial, however it is ideal to include both aerobic and resistance exercise at moderate intensity for 30 minutes, three to five times per week. Establishing a healthy weight prior to pregnancy as well as not smoking both lower the risk of GDM.