Unhealthy lifestyles and gestational diabetesBMJ 2014; 349 doi: http://dx.doi.org/10.1136/bmj.g5549 (Published 30 September 2014) Cite this as: BMJ 2014;349:g5549
- Sara J Meltzer, associate professor of medicine and obstetrics and gynecology
- Correspondence to:
Gestational diabetes mellitus is a growing problem in developed and developing countries.1 2 In a linked paper, Zhang and colleagues (doi:10.1136/bmj.g5450) report important information to help women protect themselves before and during pregnancy and reduce the enduring harm to both mothers and babies associated with gestational diabetes.3
The true incidence of gestational diabetes is difficult to know. There are wide regional and ethnic variations, and the criteria for diagnosis have been highly variable.4 This inconsistency has led WHO to reassess the diagnostic criteria for gestational diabetes. In 2013, WHO recommended screening for gestational diabetes (universally when possible) with the 75 g oral glucose tolerance test, with threshold values for diagnosis recommended initially by the IADPSG (International Association of the Diabetes and Pregnancy Study Groups): fasting plasma glucose concentration of ≤5.1 mmol/L, 10.0 mmol/L one hour postload, and 8.5 mmol/L two hours postload.5 Any one value at or above the threshold values would indicate gestational diabetes.
It would considerably improve evaluation of therapeutic interventions and long term outcomes if all investigators and studies used the same diagnostic thresholds, recognizing that there might be different country specific criteria used in a screening step before the diagnostic test. Some commentators have expressed concern that using the new thresholds would lead to a surge of diagnoses and that health systems would struggle to cope with the inevitable increase in case load and costs.6
We know that treatment for gestational diabetes works. In studies using WHO 1999 criteria, treatment reduced the risk of macrosomia by up to 52%.7 A recent study from Spain of cohorts of women before and after adoption of the WHO/IADPSG criteria for diagnosis found an increase in prevalence (from 10.5% to 35.5%).8 Despite treatment of larger numbers of women with diet, monitoring, and insulin in the approximately 20% of women not adequately controlled with diet, there were enough perinatal complications avoided to provide a cost advantage.8 It seems clear that, when possible, we should be screening, diagnosing, and treating women with gestational diabetes.
Evidence suggests that women with gestational diabetes have a dramatically increased risk of subsequently developing type 2 diabetes (relative risk 7.4) compared with women without gestational diabetes9 and that the lag time between the index pregnancy and type 2 diabetes seems to be shortening.10 Importantly, the offspring of affected mothers also seem to be at greater risk for obesity, metabolic syndrome, future gestational diabetes, and future type 2 diabetes than the offspring of unaffected mothers.11
Clearly, if there are modifiable risk factors that can decrease the proportion of women getting gestational diabetes and the need for treatment, this would be the best possible scenario. Such modification could also reduce or delay the maternal long term risks for type 2 diabetes and possibly avert similar risks in their offspring. Both these outcomes would be cost saving for health systems.12 Identification of behaviors and habits that could protect women from gestational diabetes would be an important step towards reducing the burden of this condition and surely preferable, for both women and healthcare providers, to treating abnormal glucose concentrations once diagnosed.
Zhang and colleagues analyzed data collected prospectively from the beginning of the Nurses’ Health Study in 1989 until 2001, when most of the nurse participants had passed reproductive age (70% were aged >40).3 Women who had a diet rich in cereal grains and healthy fats (based on an “Alternative Health Eating Index 2010” diet score in the top two fifths), regularly exercised moderately vigorously for least 150 minutes a week, and did not smoke were 41% less likely to develop gestational diabetes compared with other pregnant women. This figure rose to 52% if they began their pregnancy at normal weight. Importantly though, not smoking, eating well, and exercising were associated with substantial benefit even for women who were overweight or obese before pregnancy. Unfortunately, even in this motivated group of health professionals, just 16% of women reported all four lifestyle factors associated with low risk.
Zhang and colleagues found a 43% increase in risk of gestational diabetes among current smokers but no increased risk among former smokers—another good reason to encourage women planning pregnancy not to smoke.3 Perhaps not surprisingly, the greatest increase in risk was associated with pre-existing overweight or obesity, such that women with a BMI above 33 were over four times more likely to develop gestational diabetes than women who had a normal BMI before pregnancy.
A well recognized limitation of this cohort is that participants are predominantly white and all nurses. It is important for future research to determine if the apparent effect of lifestyle is the same in other ethnic groups or in populations that are less well educated about health. In the absence of a large randomized controlled trial evaluating adjustments in lifestyle before pregnancy, which might or might not be conclusive, the observational work by Zhang and colleagues provides us with valuable information.
The next big question is do we encourage all women planning pregnancy to adopt these healthier lifestyles or do we limit our attempts to those presently at higher risk? It is likely that a population health initiative strongly encouraging all women planning a pregnancy, including those at high risk, to eat better, stop smoking, and take more exercise would provide the world’s population with the largest effect for effort. Lifestyle modification is notoriously difficult, but not impossible. When combined with aggressive screening, diagnosis, and treatment, perhaps we can help to slow or even reverse current trends in obesity, metabolic disease, and cardiovascular risk that continue to rise steadily as part of a cycle.13 Although successful modification of diet, exercise, body weight, and smoking habits are not easy for anyone, the findings of Zhang and colleagues should give health professionals and women planning a pregnancy the encouragement they need to try even harder.
Cite this as: BMJ 2014;349:g5549
- Competing interests: I have read and understood the BMJ Group policy on declaration of interests and declare that I have received fees for speaking engagements and for organizing educational events. I have participated in advisory boards with companies using insulin pump technology and continuous blood glucose monitoring.
- Provenance and peer review: Commissioned; not externally peer reviewed.