Gestational diabetes mellitus (GDM) affects a significant number of women each year and is associated with a wide range of adverse outcomes for women and their babies. It is defined as glucose intolerance or high blood glucose concentration (hyperglycaemia) that starts or is first recognized during pregnancy. Hyperglycemia is associated with an elevated risk of hypertensive disorders during pregnancy, as well as preterm labor, cesarean delivery, and later metabolic disorders.1 Gestational diabetes mellitus is also a strong predictor that a woman will later develop type 2 diabetes2 and associated with an elevated risk of cardiovascular disease, particularly if the woman has a family history of type 2 diabetes.3

Gestational diabetes mellitus also raises the risk of adverse clinical consequences in the fetus. Macrosomia (birth weight >= 4000 g), large size for gestational age (LGA), and respiratory distress syndrome are linked to GDM.4 Infants who are LGA face a significantly elevated risk of injury at the time of vaginal birth, and cesarean delivery, the preferred route for the LGA infant, increases the risk of trauma to the mother, compared with the vaginal route.5 Respiratory distress syndrome, which is common among premature infants, also affects many infants born to women who have GDM, even near-term infants, with hyperglycemia associated with delay in fetal lung maturity.6

Exposure to maternal hyperglycemia also increases a child's risk of long-term complications. Children born to mothers with GDM have nearly twice the risk of childhood obesity and metabolic syndrome, compared with children born to mothers who do not have GDM.7,8

The evidence on the need to manage GDM is compelling, and dietary counseling is the main strategy for managing women with GDM.9 It is not clear, however, which dietary therapy is related to the best outcome.

OBJECTIVE

The objective of this review was to assess the effects of different types of dietary advice for women with GDM on pregnancy outcomes.

INTERVENTION/METHODS

The authors searched the Cochrane Pregnancy and Childbirth Group's Trials Register (May 17, 2012) and the WOMBAT Perinatal Trials Registry (April 17, 2012) for randomized controlled trials and cluster-randomized controlled trials assessing the effects of different types of dietary advice for women with GDM on pregnancy outcomes. The intention of the review was to compare 2 or more forms of the same type of dietary advice against each other (ie, standard dietary advice compared with individualized dietary advice, individual dietary education sessions compared with group dietary education sessions) and to compare different intensities of dietary intervention with each other (ie, single dietary counseling session compared with multiple dietary counseling sessions). Two review authors independently assessed study eligibility, extracted data, and assessed risk of bias of the included studies. Data extracted were checked for accuracy.

RESULTS

Nine trials involving 429 women (436 babies) were included in the review. All trials had small sample sizes and variation in levels of risk of bias. A total of 11 different types of dietary advice were assessed under 6 different comparisons.

* In the low-moderate GI food versus moderate-high GI food comparison, no significant differences were seen for macrosomia (risk ratio [RR], 0.45; 95% confidence interval [CI], 0.10-2.08) or LGA (RR, 0.95; 95% CI, 0.27-3.36) (2 trials, 89 babies) or caesarean section (RR, 0.66; 95% CI, 0.29-1.47; 1 trial, 63 women).

* In the low-GI diet versus high-fiber moderate-GI diet comparison, no significant differences were seen for macrosomia (RR, 0.32; 95% CI, 0.03-2.96) or LGA (RR, 2.87; 95% CI, 0.61-13.50) (1 trial, 92 babies) or caesarean section (RR, 1.80; 95% CI, 0.66-4.94; 1 trial, 88 women).

* In the energy-restricted versus energy-unrestricted diet comparison, no significant differences were seen for macrosomia (RR, 1.56; 95% CI, 0.61-3.94; 1 trial, 122 babies), LGA (RR, 1.17; 95% CI, 0.65-2.12; 1 trial, 123 babies), or caesarean section (RR, 1.18; 95% CI, 0.74-1.89; 1 trial, 121 women).

* In the low- versus high-carbohydrate diet comparison, none of the 30 babies in a single trial were macrosomic, and no significant differences in caesarean section rates were seen (RR, 1.40; 95% CI, 0.57-3.43; 1 trial, 30 women).

* In the high-monounsaturated fat versus high-carbohydrate diet comparison, neither macrosomia (RR, 0.65; 95% CI, 0.91-2.18) nor LGA (RR, 0.54; 95% CI, 0.21-1.37) (1 trial, 27 babies) showed significant differences.

* Perinatal mortality was reported in only 1 trial, which recorded no fetal deaths in either the energy-restricted or energy-unrestricted diet group.

CONCLUSIONS

Data for most comparisons were only available from single studies, and they were too small for reliable conclusions to be drawn. There was lack of reporting on prespecified primary outcomes, and limited data were reported on the prespecified outcomes for each of the 6 comparisons. Only 1 trial reported early postnatal outcomes. No trial reported long-term health outcomes for women and their babies. No data were reported on health service cost or women's quality of life.

On the basis of the current available evidence, the review did not report any significant benefits of the diets investigated. Further larger trials with sufficient power to assess the effects of different diets for women with GDM on maternal and infant health outcomes and the inclusion of outcomes such as longer-term health outcomes for women and their babies, women's quality of life, and health service cost are needed.

IMPLICATIONS FOR PRACTICE

Although the evidence on the most effective dietary advice for women with GDM remains unclear, the evidence for the need to manage GDM as effectively as possible and reduce and avoid negative clinical outcomes is strong. To this effect, all nurses can play a role in promoting a healthy and balanced diet for women during pregnancy. Most guidelines and original studies on the care of women with GDM do not describe the role of the nurse as an active one. The role of the general practitioner, endocrinologist, or dietitian is generally specified. The roles of the nurse practitioner, clinical nurse specialist, diabetes nurse, and direct care nurse appear to be overlooked resources in the field. Advanced practice nurses and diabetes nurses may offer a pathway for the assessment and management of more complex care situations. However, identifying gestational diabetes as early as possible and providing ongoing support with dietary change are important roles for all nurses, regardless of specialty or setting. In planning future trials to assess the effectiveness of dietary advice for women with GDM, researchers and clinicians are encouraged to collaborate with nurses, not only to promote the intervention but also to actively support women to implement change on a day-to-day basis.

References