The Relationship Between Maternal Glycemia and Perinatal Outcome

Fetal macrosomia and shoulder dystocia in women with gestational diabetes: risks amenable to treatment?

Fetal macrosomia and maternal diabetes are independent risk factors for shoulder dystocia, an obstetrical emergency that may cause permanent neonatal injury. Randomized trials of glycemic control in pregnancies complicated by gestational diabetes reveal decreased rates of macrosomia and shoulder dystocia among those treated. However, definitions of gestational diabetes vary and a specific glycemic threshold for clinically significant risk reduction remains to be delineated. This review discusses risks associated with gestational diabetes including macrosomia (birth weight above 4000-4500 g) and delivery-related morbidity, specifically, shoulder dystocia. Subsequently, we will review recent randomized trials assessing the impact of glycemic control on these delivery-related morbidities. Finally, we will examine a large observational study that found associations with delivery-related morbidity and hyperglycemia below current diabetic thresholds, observations which may suggest reexamination of current diagnosis guidelines for gestational diabetes.

Mild gestational diabetes: towards a redefined threshold?

Gestational diabetes mellitus (GDM), the most common medical complication of pregnancy, is defined as carbohydrate intolerance resulting in hyperglycemia of variable severity with onset or first recognition during pregnancy. In reality, gestational diabetes mellitus is a spectrum of maternal hyperglycemia caused or exacerbated by pregnancy, in which blood glucose levels lie along a continuum, associated with a wide spectrum of metabolic abnormalities and conferring varying degrees of pregnancy-related risk. In recent years, the WHO diagnostic thresholds in current use have been called into question, as increasing evidence mounts that 'mild gestational diabetes' confers increased maternal and fetal risk, despite glucose levels falling below current thresholds. This review summarizes the existing evidence, unanswered questions and health service implications related to women with so-called 'mild' gestational diabetes.

The effect of race/ethnicity on adverse perinatal outcomes among patients with gestational diabetes mellitus

OBJECTIVE

The purpose of this study was to determine racial/ethnic differences in perinatal outcomes among women with gestational diabetes mellitus.

STUDY DESIGN

We conducted a retrospective cohort study of 32,193 singleton births among women with gestational diabetes mellitus in California from 2006, using Vital Statistics Birth and Death Certificate and Patient Discharge Data. Data were divided by race/ethnicity: white, black, Hispanic, or Asian. Multivariable logistic regression was used to analyze associations between race/ethnicity and adverse outcomes that were controlled for potential confounders. Outcomes included primary cesarean delivery, preeclampsia, neonatal hypoglycemia, preterm delivery, macrosomia, fetal anomaly, and respiratory distress syndrome.

RESULTS

Compared with women in other races, black women had higher odds of preeclampsia (adjusted odds ratio [aOR], 1.57; 95% confidence interval [CI], 1.47-1.95), neonatal hypoglycemia (aOR, 1.79; 95% CI, 1.07-3.00), and preterm delivery <37 weeks' gestation (aOR, 1.56; 95% CI, 1.33-1.83). Asian women had the lowest odds of primary cesarean delivery (aOR, 0.75; 95% CI, 0.69-0.82), large-for-gestational-age infants (aOR, 0.40; 95% CI, 0.33-0.48), and neonatal respiratory distress syndrome (aOR, 0.54; 95% CI, 0.40-0.73).

CONCLUSION

Perinatal outcomes among women with gestational diabetes mellitus differ by race/ethnicity and may be attributed to inherent sociocultural differences that may impact glycemic control, the development of chronic comorbidities, genetic variability, and variation in access to prenatal care, and quantity and quality of prenatal care.

Association of genetic variants of melatonin receptor 1B with gestational plasma glucose level and risk of glucose intolerance in pregnant Chinese women

Background

This study aimed to explore the association of MTNR1B genetic variants with gestational plasma glucose homeostasis in pregnant Chinese women.

Methods

A total of 1,985 pregnant Han Chinese women were recruited and evaluated for gestational glucose tolerance status with a two-step approach. The four MTNR1B variants rs10830963, rs1387153, rs1447352, and rs2166706 which had been reported to associate with glucose levels in general non-pregnant populations, were genotyped in these women. Using an additive model adjusted for age and body mass index (BMI), association of these variants with gestational fasting and postprandial plasma glucose (FPG and PPG) levels were analyzed by multiple linear regression; relative risk of developing gestational glucose intolerance was calculated by logistic regression. Hardy-Weinberg Equilibrium was tested by Chi-square and linkage disequilibrium (LD) between these variants was estimated by measures of D′ and r².

Results

In the pregnant Chinese women, the MTNR1B variant rs10830963, rs1387153, rs2166706 and rs1447352 were shown to be associated with the increased 1 hour PPG level (p = 8.04×10⁻¹⁰, 5.49×10⁻⁶, 1.89×10⁻⁵ and 0.02, respectively). The alleles were also shown to be associated with gestational glucose intolerance with odds ratios (OR) of 1.64 (p = 8.03×10⁻¹¹), 1.43 (p = 1.94×10⁻⁶), 1.38 (p = 1.63×10⁻⁵) and 1.24 (p = 0.007), respectively. MTNR1B rs1387153, rs2166706 were shown to be associated with gestational FPG levels (p = 0.04). Our data also suggested that, the LD pattern of these variants in the studied women conformed to that in the general populations: rs1387153 and rs2166706 were in high LD, they linked moderately with rs10830963, but might not linked with rs1447352;rs10830963 might not link with rs1447352, either. In addition, the MTNR1B variants were not found to be associated with any other traits tested.

Conclusions

The MTNR1B is likely to be involved in the regulation of glucose homeostasis during pregnancy.

Maternal BMI, glucose tolerance, and adverse pregnancy outcomes

OBJECTIVE

The purpose of this study was to estimate the association of pregravid body mass index (BMI), independent of 3-hour oral glucose tolerance test (OGTT) results, with pregnancy outcome.

STUDY DESIGN

In this secondary analysis of a cohort of women with untreated mild gestational glucose intolerance, which was defined as a 50-g glucose loading test between 135 and 199 mg/dL and fasting glucose level of <95 mg/dL, we modeled the association between pregravid BMI, OGTT results, and both pregnancy complications and neonatal adiposity.

RESULTS

Among 1250 participants, both pregravid BMI and glucose at hour 3 of the OGTT were associated with increased risk of gestational hypertension. Maternal pregravid BMI also was associated positively with large-for-gestational-age infants; both maternal BMI and fasting glucose were associated with birthweight z-score and neonatal fat mass.

CONCLUSION

Among women with untreated mild gestational glucose intolerance, pregravid BMI is associated with increased gestational hypertension, birthweight, and neonatal fat mass, independent of OGTT values.

The hyperglycemia and adverse pregnancy outcome study: associations of GDM and obesity with pregnancy outcomes

OBJECTIVE

To determine associations of gestational diabetes mellitus (GDM) and obesity with adverse pregnancy outcomes in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study.

RESEARCH DESIGN AND METHODS

Participants underwent a 75-g oral glucose tolerance test (OGTT) between 24 and 32 weeks. GDM was diagnosed post hoc using International Association of Diabetes and Pregnancy Study Groups criteria. Neonatal anthropometrics and cord serum C-peptide were measured. Adverse pregnancy outcomes included birth weight, newborn percent body fat, and cord C-peptide >90th percentiles, primary cesarean delivery, preeclampsia, and shoulder dystocia/birth injury. BMI was determined at the OGTT. Multiple logistic regression was used to examine associations of GDM and obesity with outcomes.

RESULTS

Mean maternal BMI was 27.7, 13.7% were obese (BMI ≥33.0 kg/m(2)), and GDM was diagnosed in 16.1%. Relative to non-GDM and nonobese women, odds ratio for birth weight >90th percentile for GDM alone was 2.19 (1.93-2.47), for obesity alone 1.73 (1.50-2.00), and for both GDM and obesity 3.62 (3.04-4.32). Results for primary cesarean delivery and preeclampsia and for cord C-peptide and newborn percent body fat >90th percentiles were similar. Odds for birth weight >90th percentile were progressively greater with both higher OGTT glucose and higher maternal BMI. There was a 339-g difference in birth weight for babies of obese GDM women, compared with babies of normal/underweight women (64.2% of all women) with normal glucose based on a composite OGTT measure of fasting plasma glucose and 1- and 2-h plasma glucose values (61.8% of all women).

CONCLUSIONS

Both maternal GDM and obesity are independently associated with adverse pregnancy outcomes. Their combination has a greater impact than either one alone.

Screening for gestational diabetes mellitus: are the criteria proposed by the international association of the Diabetes and Pregnancy Study Groups cost-effective?

OBJECTIVE

The International Association of the Diabetes and Pregnancy Study Groups (IADPSG) recently recommended new criteria for diagnosing gestational diabetes mellitus (GDM). This study was undertaken to determine whether adopting the IADPSG criteria would be cost-effective, compared with the current standard of care.

RESEARCH DESIGN AND METHODS

We developed a decision analysis model comparing the cost-utility of three strategies to identify GDM: 1) no screening, 2) current screening practice (1-h 50-g glucose challenge test between 24 and 28 weeks followed by 3-h 100-g glucose tolerance test when indicated), or 3) screening practice proposed by the IADPSG. Assumptions included that 1) women diagnosed with GDM received additional prenatal monitoring, mitigating the risks of preeclampsia, shoulder dystocia, and birth injury; and 2) GDM women had opportunity for intensive postdelivery counseling and behavior modification to reduce future diabetes risks. The primary outcome measure was the incremental cost-effectiveness ratio (ICER).

RESULTS

Our model demonstrates that the IADPSG recommendations are cost-effective only when postdelivery care reduces diabetes incidence. For every 100,000 women screened, 6,178 quality-adjusted life-years (QALYs) are gained, at a cost of $125,633,826. The ICER for the IADPSG strategy compared with the current standard was $20,336 per QALY gained. When postdelivery care was not accomplished, the IADPSG strategy was no longer cost-effective. These results were robust in sensitivity analyses.

CONCLUSIONS

The IADPSG recommendation for glucose screening in pregnancy is cost-effective. The model is most sensitive to the likelihood of preventing future diabetes in patients identified with GDM using postdelivery counseling and intervention.

Diagnosing gestational diabetes: can expert opinions replace scientific evidence?

Preventive medical interventions should be based on the highest level of scientific evidence. Actual criteria for diagnosing gestational diabetes mellitus (GDM) are neither uniform nor based on pregnancy outcomes. An expert panel from the International Association of Diabetes in Pregnancy Study Groups recently proposed that all pregnant women undergo a one-step 75 g OGTT, and defined new lower cut-off points to diagnose GDM (Metzger BE et al. Diabetes Care 33: 676-682). These criteria will double the prevalence of GDM, as 18% of all pregnant women will be labelled as abnormal. A recent article in Diabetologia (Ryan EA 54:480-486) claimed that maternal glucose is a weak predictor of big babies, that a single OGTT is poorly reproducible, and that expected benefits from intervention would be, at best, modest. This Commentary discusses other objections and argues that guidelines on any new GDM diagnostic strategy should be based on the results of randomised controlled trials rather than on disputable expert opinions.