Effect of exercise on glycaemic control and pregnancy outcomes in women with gestational diabetes mellitus: A review

INTRODUCTION

During pregnancy, a significant number of women suffer from gestational or pre-existing type 1 or type 2 diabetes.^[1-3] Of these three types, gestational diabetes mellitus (GDM) is the most common, with a worldwide prevalence rate of 16.4%, and is constantly on the rise.^[4] GDM is defined as ‘carbohydrate intolerance resulting in hyperglycaemia of variable severity with onset or first recognition during pregnancy.’^[5] The recent World Health Organization report^[6] suggests that the diagnosis of GDM should be considered positive if the pregnant women have either a plasma glucose level between 5.1 and 6.9 mmol/L under fasting conditions, or more than 10.0 mmol/L 1 h after 75 g glucose intake, or between 8.5 and 11.0 mmol/L 2 h after glucose intake.

Pregnancies with GDM are usually high risk and the condition can trigger many adverse outcomes for the mother as well as the neonate.^[7] Some of the most common are pre-eclampsia, perineal trauma, pregnancy-induced hypertension, and increased chances of caesarean section.^[8-10] In addition, it is expected that almost half of the mothers with GDM will eventually develop diabetes mellitus type 2 later in their lives.^[11] Further, possible neonatal complications include macrosomia, shoulder dystocia, birth trauma, hypoglycaemia, hyperbilirubinemia, polycythaemia, respiratory distress syndrome, and jaundice.^[12,13] Despite its severe repercussions, GDM is preventable, and if detected at an early stage, it can be reversed through appropriate interventions, and consequently, the majority of the associated risks can be avoided.^[14-16]

The management of GDM varies depending upon the resources available. In daily practice, physicians use various medical and non-medical (or combination of both) interventions to treat GDM. The most common medical interventions include oral hypoglycaemic drugs and insulin therapy.^[17] Although insulin therapy is the preferred pharmacological treatment modality, it has its own challenges.^[18] For this reason, non-pharmacological intervention should be recommended as the first- line treatment option. This involves adopting lifestyle modifications such as diet control and exercise.^[19] Women with GDM are usually advised to first try controlling their glucose levels through diet control alone or in combination with physical exercise.^[20] The literature suggests that over 75% of GDM cases achieve glycaemic control with lifestyle modifications alone.^[15,21]

Exercise is defined as ‘physical activities consisting of planned and repetitive body movements to improve physical fitness.’^[22] Physical exercise is considered essential to maintain a healthy lifestyle during pregnancy.^[23] Most gynecological and obstetrical guidelines recommend 25–30 min of mild to moderate exercise per day during pregnancy.^[24,25]

Exercises which are considered safe and acceptable during an uncomplicated pregnancy are: Walking, running or jogging, swimming, stationary cycling, low-intensity aerobics, modified Pilates, yoga, resistance training, and stretching exercises.^[24] Exercise in cases of uncomplicated pregnancies has been known to be beneficial and may have long- term positive effects on maternal health.^[26] The potential benefits include reduced stress and depression, improved cardiorespiratory fitness, reduced likelihood of urinary incontinence and lumbar pain, less gestational weight gain, better glycaemic control, and minimal risk of diabetes during pregnancy.^[26-28] However, these reported that the benefits of exercise might not be generalizable to pregnant women with GDM.

Although it is well known that exercise is beneficial during an uncomplicated pregnancy, certain challenges exist that might restrict women from exercising. The known barriers are fatigue, nausea, inactivity prior to pregnancy, and/or restricted mechanical movements at a later stage of pregnancy.^[29] In addition, the support of a qualified physical trainer may not be readily available at all antenatal centres, and the attending physician may recommend exercises that are neither based on evidence nor on standard guidelines.^[30,31] In women with diabetes, it is usually recommended to take certain precautions because of the differences in physiology and possible interaction with anti- diabetic drugs taken during pregnancy. This complicated and sensitive condition demands the application of evidence- based exercise guidelines to improve maternal and neonatal health outcomes.^[32]

To realize the optimal benefits of exercise without any complications or risks, it is essential to understand which type of exercise should be used, and with what regularity, duration, and intensity.^[32,33] Several interventional studies have sought to clarify the impact of exercise on GDM and its effects on pregnancy outcomes. However, due to the disparity in reported results, there is currently no consensus on recommendations for the type, duration, and intensity of the known exercises. Therefore, this review aims to consolidate the evidence in the literature concerning the various exercise interventions used so far by women with GDM and their possible effects on glycaemic control and pregnancy outcomes.

MATERIALS AND METHODS

To achieve the objectives of this study, a literature search was performed using Medline, PubMed, Web of Science, Cochrane Library, and Scopus. All the peer-reviewed articles published in the past 10 years (2009–2019) were retrieved and their abstracts screened. Abstracts were screened by using the following inclusion criteria: (1) The study should be randomized controlled trials (RCTs) involving human female subjects with GDM in both exercise and control group (CG), (2) the trial should be aiming to assess the impact of different exercise interventions, (3) the study should report any maternal or newborn outcome, (4) the article should be written in English, and (5) the article should be published in a peer-reviewed journal and within the decided timeframe (2009–2019). This timeline was selected because the objective of this review study was to give a literature update on what has been reported in the past decade while exploring the effect of exercise on glycaemic control and pregnancy outcomes. Those articles in which other medical or non-medical interventions were studied in combination with physical exercise were excluded from the study. Furthermore, excluded were studies which were not randomized. Papers written in languages other than English were also excluded from the study. The keywords used when exploring the literature included ‘non- pharmacological strategies,’ ‘non-medical strategies,’ ‘non- medical treatment,’ ‘pregnancy,’ ‘gestational diabetes,’ ‘GDM,’ ‘exercise,’ ‘glycaemic control,’ ‘pregnancy outcomes,’ ‘maternal outcomes,’ and ‘neonatal outcomes.’

RESULTS

A total of 11 studies were identified, all of which met the inclusion criteria for this review [Table 1].^[34-44] In all the extracted articles, standard antenatal care was given to all the patients in the intervention group, in addition to performing different physical exercises; whereas, only standard antenatal care was given to the CG during the trial.

DISCUSSION

GDM is a metabolic problem with known negative effects on maternal and neonatal health. In this review, the researcher aimed to consolidate the literature reporting the effect of exercise on glycaemic control and pregnancy outcomes. The findings suggest that exercise is safe for women with GDM and that it may offer almost similar fitness benefits to suffering individuals as it does to those without diabetes. Furthermore, exercising women with GDM acquire better glucose control than non-exercising women. It can also be derived from the findings in the literature that an exercise intervention during pregnancy can surely help to avoid or at least delay the necessity for insulin.^[38,42] Studies also suggest exercise alone can reverse GDM and reduce the chances of developing diabetes mellitus type 2 in the long term.^[11,32]

While the current literature offers reassurance that exercising women with GDM might not experience hypoglycaemia, the possibility of its occurrence cannot be ignored as it is seriously harmful to both the mother and the foetus. Therefore, women with GDM should seek the professional support of a certified trainer, or at least avoid exercising without supervision.^[45] In addition, workout measuring devices (ActiGraph and Omron) with known reliability and validity for use in pregnancy can be worn to keep physical activities in check.^[46] Nowadays, many commercial companies offer wearable activity trackers and smart watches, which can help to monitor calorie consumption. These smart watches are also known as a source of motivation and commitment to exercise goals.^[47]

After critically analysing the reported interventional studies, it can be concluded that an exercise of 15–30 min in low to moderate intensity is ideal in women with GDM. This is in line with the Canadian guidelines for physical activity throughout pregnancy,^[48] and the recommendations of the American Diabetes Association.^[49] GDM is typically diagnosed between 24 and 28 weeks of gestation, which offers an exercise window of 12–16 weeks duration. Between different types of exercises, it is up to the patient to choose according to her preference and practical options. However, certain high risk or high-intensity exercises raise safety concerns, and therefore these should be avoided, that is, skiing, road cycling, surfing, football, hockey, boxing, hot yoga, scuba diving, sky diving, and non-modified Pilates.^[24]

It should be noted that the available evidence on which these recommendations have been based is limited. Moreover, few studies have evaluated the effect of exercise on pregnancy outcomes, which further restricts our understanding of the topic under discussion. Future researchers should convene longitudinal clinical trials at various gestational time points as a way to investigate in detail the effects of different exercise interventions on pregnancy outcomes. Another interesting factor would be to investigate the impact of emerging technologies, such as fitness trackers and smart watches, when monitoring glycaemic control among exercising women with GDM.

Certain limitations of this review need to be reported. In this study, the literature from the past 10 years has been reviewed and trials reported before 2009 have been excluded from the study. This review focuses on the effect of exercise in pregnant women with gestational diabetes only and does not include type 1 and 2 diabetes. A further limitation is that studies reporting the effect of exercise interventions only were included in the study. Trials involving mixed interventions (diet control and exercise), with or without pharmacological support, were not included in the study. Although all the reviewed articles were RCTs, assessment of the risk of bias was not performed, as it went beyond the objectives of this review.

CONCLUSION

For women with GDM, exercise is beneficial as a means of achieving better glycaemic control, thereby improving maternal and neonatal outcomes. It is recommended that pregnant women should exercise for 15–30 min from GDM diagnosis until the end of the gestational period. Patients can choose the type of exercise intervention they prefer, considering factors such as comfort, available resources, and providing the exercise chosen is of light to moderate intensity.