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Effect of Treatment of Gestational Diabetes Mellitus on Pregnancy Outcomes

Background: Gestational diabetes mellitus is commonly associated with serious maternal and perinatal complications, however screening and treatment of glucose intolerance of pregnancy is highly controversial due to the unknown benefits associated with management of gestational diabetes.

Objective: This study was designed to determine if screening and treatment of gestational diabetes through dietary advice, blood glucose monitoring, and insulin treatment could improve the outcomes of mothers and infants compared to mothers receiving routine care without universal screening standards for gestational diabetes.

Methods: This represented a randomized, placebo controlled, parallel group study. One thousand women were assigned to the study between September 1993 and June 2003. To be included in the study, women had to be between 16 and 30 weeks gestation of a singleton or twin pregnancy, attended antenatal clinics at the collaborating hospitals, and had one or more risk factors for gestational diabetes or a positive 50-g oral glucose challenge test and had a 75-g oral glucose tolerance test at 24 to 34 weeks that was less than 7.8 mmol/L after an overnight fast and between 7.8 and 11.0 mmol/L at two hours. Women were excluded if they had more severe glucose impairment, were previously treated for gestational diabetes, or had active chronic systemic disease other than essential hypertension. Subjects were randomized to either the intervention group or the routine care group. Four hundred ninety women in the intervention group received a slip indicating a diagnosis of glucose intolerance of pregnancy and their plan for intervention. Each woman received individualized dietary advice from a dietician, self monitored their blood glucose levels on a scheduled basis, and received insulin therapy as needed. Five hundred ten women in the routine care group received a slip stating that they did not have gestational diabetes. This group represented clinical care in which screening for gestational diabetes is not available. The primary outcomes for infants was a composite measure of serious perinatal complications (death, shoulder dystocia, bone fracture, nerve palsy), admission to the neonatal nursery, and jaundice requiring phototherapy. For mothers, primary outcomes included the need for induction of labor or cesarean section. Maternal health status assessed by the Medical Outcomes Study 36-Item Short Form General Health survey, and maternal psychological outcomes such as anxiety, depression, and health related quality of life were assessed by means of a questionnaire mailed to patients six weeks after enrollment and 3 months post partum. Secondary measures included the components of the composite primary outcome, gestational age at birth, birth weight, and other measures of health for the infant. Secondary measures for the mother were number of prenatal visits to health care providers, mode of birth, weight gain during pregnancy, number of antenatal admissions, and absence of pregnancy-induced hypertension. The intention to treat principle was conducted for the primary analysis. A log binomial regression was used to calculate relative risk with a 95% confidence interval. Continuous variables were analyzed by means of analysis of variance if they were normally distributed and nonparamentric tests were used if the distribution was not normal. Step-down Sidak adjustments were made for analyses involving multiple primary clinical end points. Power of the study was reported at 80% with 1000 subjects enrolled.

Results: One thousand women and 1030 infants completed the study, however only 682 women completed the questionnaires six weeks after enrollment and 573 completed the questionnaires 3 months post partum. The rate of serious perinatal outcomes was significantly lower in the intervention group compared to the routine care group (1% and 4% respectively P=0.01; with a relative risk of 0.32 (95% CI 0.14-0.73 P=0.04)). The number needed to treat to prevent a serious outcome in an infant was 34 (95% CI 20-103). A higher percentage of infants born in the invention group compared to the routine care group were admitted to the neonatal nursery (71% and 61% respectively; adjusted P=0.01; with a relative risk of 1.15 (95% CI 1.05 –1.26 P=0.002)). Length of stay in the nursery, jaundice requiring phototherapy, and rate of cesarean delivery did not differ between the groups (P=0.81, P=0.72, P=0.73 respectively). Induction of labor was more significant in the intervention group (P<0.001; with a relative risk of 1.31 (95% CI 1.10-1.56)). For the questionnaires related to maternal health and psychological status, the intervention group scored significantly better in the physical functioning, general health, overall physical component, and in postnatal depression scores. All P-values and CI can be seen in table 3. No perinatal deaths were reported in the intervention group, but five deaths were reported in the routine care group. In the intervention group, lower birth weights were seen (P<0.001), infants were born at an earlier gestational age, fewer were large for gestational age (P<0.001), and fewer had macrosomia (P<0.001; 95%). In the intervention group, there were fewer antenatal clinic visits (P<0.001), but more visits to the physician (P<0.001) and to a dietician and a diabetes educator (P<0.001). One hundred women (20%) in the intervention group received insulin therapy, compared to 17 (3%) in the routine care group. The authors concluded that treatment of gestational diabetes in the form of dietary advice, blood glucose monitoring, and insulin therapy as required for glycemic control reduced the rate of serious perinatal complications.

Strengths: No conflicts of interest existed between the authors and the study support. None of the funding bodies were involved in any part of the design or analysis of the study. A power of 80% was sufficient in most parts of the study, with the exception of the questionnaires. The statistical tests were used appropriately. There were no significant differences at baseline among the women entering the study.

Weaknesses: Women were recruited over a ten-year period from 1993 to 2003. This is a long period of time to try and standardize all women to the same care. In addition, not all women would be seeing the same doctor, dietician, and diabetes educator over this time span and standards of care in general could have changed. This could have created variability within the intervention and routine care group. Specific guidelines or results on insulin use, duration, type, and the blood glucose levels of the women were not given within the study. There is no way of determining if the use of insulin was effective and how to apply these results in a clinical setting. There was no data indicating the interventions reduced the patients blood glucose levels or it improvement in blood glucose levels contributed to the improvement in outcomes. The actual improvement in perinatal outcomes in the intervention group could have been due to the doctors’ knowledge of the risk for gestational diabetes and enhanced caution used because of this knowledge, rather than the actual interventions used in the study. Compliance was also not addressed. Ethical issues were raised concerning the lack of knowledge the women had about their diagnosis of gestational diabetes.

Conclusion: The study did not present a strong correlation between the intervention group and a reduction in serious complications among the mother and child. Statistically significant results were present, however the reason behind the improved outcomes was unclear. Further studies need to address the difference between actual interventions in women compared to knowledge by the physician of the mothers’ glucose intolerance.

Crowther CA, Hiller JE, Moss JR, McPhee AJ, Jeffries WS, Robinson JS. Effect of treatment of gestational diabetes mellitus on pregnancy outcomes. N Engl J Med 2005;352:2477-86.

Emily DeVault, Pharm.D. Candidate