What is the issue?
Up to a quarter of pregnant women develop gestational diabetes mellitus (GDM) depending on their ethnicity and the diagnostic criteria used. GDM is evident as high blood sugar levels (hyperglycaemia) during pregnancy and is associated with an increased risk of developing high blood pressure (hypertension) and protein in the urine during pregnancy (pre-eclampsia). These women are more likely to have a caesarean birth, develop type 2 diabetes, postnatal depression, and cardiovascular disease later on in life. The high blood sugar levels that are associated with GDM often return to normal as soon as the baby is born, but women with GDM are at risk of again developing GDM in future pregnancies. Babies whose mothers have been diagnosed with GDM are at an increased risk of having a birthweight greater than 4000 g, increased risk of birth trauma because of their size and developing breathing difficulties after birth. The babies are also at risk of future obesity and type 2 diabetes.
Why is this important?
Women with GDM are treated with the aims of controlling high maternal blood sugar levels and reducing the risks of GDM for the mother and the baby. Blood sugar control is monitored by measuring blood sugar concentrations to ensure they are maintained within a pre-defined level or range. The blood sugar results are usually obtained by the mother using a finger prick to collect a drop of her blood on a test strip, which is inserted into a small machine (a glucometer) that reads the sugar level of the blood on the test strip. The glucometer reading alerts the pregnant woman to her current blood sugar level and is used to guide her treatment. For example, how many units of insulin she requires before eating. However, it is currently unclear how to advise pregnant women with newly diagnosed GDM what is the most effective blood sugar range to aim for and guide treatment.
What evidence did we find?
We searched for evidence on 31 January 2016 and found one small randomised controlled trial (abstract only) that was of poor quality and involved 180 women from Canada.The trial compared two blood sugar ranges, one strict the other more liberal, and reported a very few health outcomes for the pregnant woman and her baby.
The trial did not provide any data for this review's main outcomes. For the woman, these related to the development of high blood pressure and protein in the urine during pregnancy, developing type 2 diabetes. For the baby, these outcomes related to death of the baby, increased birthweight, increased risk of birth trauma because of their size, and disability.
More women were on insulin in the strictly controlled group (but this result is based on very low quality evidence). No clear differences were reported for caesarian section rates. No other secondary outcome data for women with GDM relevant to this review were reported. No differences were reported for the number of babies that had a birthweight greater than 4000 g or were small-for-gestational age. No other secondary outcomes for the babies relevant to this review were reported.The study did not report on adverse events.
What does this mean?
This review found that there is not yet enough evidence from randomised controlled trials to determine the best blood sugar range for improving health for pregnant women with GDM and their babies. Four studies are ongoing but not yet complete. More high-quality studies are needed that compare different targets for blood sugar levels and assess both short-term and long-term health outcomes for women and their babies to guide treatment. Studies should include women's experiences and assess health services costs.
This review is based on a single study (involving 180 women) with an unclear risk of bias. The trial (which was only reported in a conference abstract) did not provide data for any of this review's primary outcomes but did provide data for a limited number of our secondary outcomes. There is insufficient evidence to guide clinical practice for targets for glycaemic control for women with GDM to minimise adverse effects on maternal and fetal health. Glycaemic target recommendations from international professional organisations for maternal glycaemic control vary widely and are reliant on consensus given the lack of high-quality evidence.
Further high-quality trials are needed, and these should compare different glycaemic targets for guiding treatment of women with GDM, assess both short-term and long-term health outcomes for women and their babies, include women's experiences and assess health services costs. Four studies are ongoing.
Gestational diabetes mellitus (GDM) has major short- and long-term implications for both the mother and her baby. GDM is defined as a carbohydrate intolerance resulting in hyperglycaemia or any degree of glucose intolerance with onset or first recognition during pregnancy from 24 weeks' gestation onwards and which resolves following the birth of the baby. Rates for GDM can be as high as 25% depending on the population and diagnostic criteria used and rates are increasing globally. Risk factors associated with GDM include advanced maternal age, obesity, ethnicity, family history of diabetes, and a previous history of GDM, macrosomia or unexplained stillbirth. There is wide variation internationally in glycaemic treatment target recommendations for women with GDM that are based on consensus rather than high-quality trials.
To assess the effect of different intensities of glycaemic control in pregnant women with GDM on maternal and infant health outcomes.
We included one randomised controlled trial. Cluster-randomised and quasi-randomised controlled trials were eligible for inclusion.
We used the methods described in the Cochrane Handbook for Systematic Reviews of Interventions for carrying out data collection, assessing study quality and analysing results. Two review authors independently assessed trial eligibility for inclusion, evaluated methodological quality and extracted data for the one included study. We sought additional information from one trial author but had no response. We assessed the quality of evidence for selected outcomes using the GRADE approach.
We included one Canadian trial of 180 women, recruited between 20 to 32 weeks' gestation, who had been diagnosed with GDM. Data from 171 of the 180 women were published as a conference abstract and no full report has been identified. The overall risk of bias of the single included study was judged to be unclear.
The included trial did not report on any of this review's primary outcomes. For the mother, these were hypertension disorders of pregnancy or subsequent development of type 2 diabetes. For the infant, our primary outcomes were (perinatal (fetal and neonatal) mortality; large-for-gestational age; composite of death or severe morbidity or later childhood neurosensory disability).
The trial did report data relating to some of this review's secondary outcomes. There was no clear difference in caesarean section rates for women assigned to using strict glycaemic targets (pre-prandial 5.0 mmol/L (90 mg/L) and at one-hour postprandial 6.7 mmol/L (120 mg/dL)) (28/85, 33%) when compared with women assigned to using liberal glycaemic targets (pre-prandial 5.8 mmol/L (103 mg/dL) and at one-hour postprandial 7.8 mmol/L (140 mg/dL)) (21/86, 24%) (risk ratio (RR) 1.35, 95% confidence interval (CI) 0.83 to 2.18, one trial, 171 women; very low quality). Using the GRADE approach, we found the quality of the evidence to be very low for caesarean section due to poor reporting of risk of bias, imprecision and publication bias. Strict glycaemic targets were associated with an increase in the use of pharmacological therapy (identified as the use of insulin in this study) (33/85; 39%) compared with liberal glycaemic targets (18/86; 21%) (RR 1.85, 95% CI 1.14 to 3.03; one trial, 171 women). CIs are wide suggesting imprecision and caution is required when interpreting the data. No other secondary maternal outcome data relevant to this review were reported. For the infant, there were no clear differences between the groups of women receiving strict and liberal glycaemic targets for macrosomia (birthweight greater than 4000 g) (RR 1.35, 95% CI 0.31 to 5.85, one trial, 171 babies); small-for-gestational age (RR 1.12, 95% CI 0.48 to 2.63, one trial, 171 babies); birthweight (mean difference (MD) -92.00 g, 95% CI -241.97 to 57.97, one trial, 171 babies) or gestational age (MD -0.30 weeks, 95% CI -0.73 to 0.13, one trial, 171 babies). Adverse effects data were not reported. No other secondary neonatal outcomes relevant to this review were reported.