A significant difference in frequency of cesarean deliveries was noted between the before and after groups, even among patients not diagnosed with gestational diabetes (Table 2). However, there was no significant difference in the adjusted odds of cesarean deliveries resulting from arrest disorders between the two groups. Table 3 shows that the odds of having a primary cesarean delivery were significantly greater in the after group. However, no significant difference was noted in the odds of having LGA (greater than the 90th percentile for age and sex) between the before and after groups. In contrast, a statistically significant difference in LGA neonates, macrosomia, and primary cesarean delivery was noted between patients with different BMIs at the first prenatal visit (Table 4).
In our study cohort, the use of the one-step IADPSG protocol for gestational diabetes screening instead of the two-step approach using the Carpenter-Coustan criteria cutoffs was associated with an increase in the rate of gestational diabetes from 17% to 27%. However, the IADPSG approach was not associated with a lower rate of LGA neonates, macrosomia, neonatal intensive care unit admissions, preterm births, preeclampsia, shoulder dystocia, or hyperbilirubinemia.
In contrast, a number of studies have noted that treating patients with glucose intolerance below the Carpenter-Coustan criteria can reduce the number of LGA fetuses. Bonomo et al and Bevier et al showed that treating women with an elevated 50-g glucose challenge test but a normal 100-g glucose tolerance test resulted in fewer LGA neonates.14,15 Crowther et al16 showed that treating women diagnosed with gestational diabetes by a 50- g oral glucose challenge test followed by a 75-g oral glucose tolerance test decreased serious perinatal complications. The IADPSG extrapolated from these studies that expanding the number of patients diagnosed with and treated for gestational diabetes would result in fewer LGA neonates. However, the current study does not support that hypothesis. The cutoffs chosen by the IADPSG, based on the results of the Hyperglycemia and Adverse Pregnancy Outcomes study,17,18 may be too low and thus result in too many patients being treated as having gestational diabetes. Different cutoff values need to be evaluated and more attention needs to be focused on controlling prepregnancy BMI.
Interestingly, this study reaffirmed other studies that found a high correlation between BMI and proportion of LGA neonates.8,19,20 Black et al followed women who were found to have IADPSG-defined gestational diabetes but who were not treated. They found that prepregnancy maternal obesity had a greater effect on the proportion of LGA neonates than did untreated gestational diabetes.19 Di Benedetto et al20 evaluated nondiabetic women and found that those who were obese and overweight had a significantly greater percentage of macrocosmic neonates than women who were not obese and not diabetic. Pettitt et al1 in evaluating gestational diabetes in Pima Indians noted that maternal weight, maternal age, and third-trimester glucose values were so closely related that it was difficult to discern which had the greatest effect. These studies taken together with the current one suggest that a renewed focus on reducing prepregnancy overweight and obesity rates may result in a smaller proportion of LGA neonates.
A strength of this study is that the same physicians treated patients who came from the same community using the same treatment for gestational diabetes for both the before and after time periods. However, this strength may limit the generalizability of the results. The population studied had a majority Hispanic and Pacific Islander and Asian ethnicity. For this population, the rate of gestational diabetes by either testing criteria is higher than what has been reported in other studies with more diverse populations.21 Furthermore, as a retrospective analysis, this study has inherent limitations. Changes in practice patterns do occur over time as noted by the increase in cesarean deliveries even in patients who did not have gestational diabetes. However, the increase in total cesarean deliveries between the before and after groups was even greater. The difference between the increase that can be accounted for by changes in practice pattern and the total increase suggests that changing the testing criteria contributed to the increase in cesarean deliveries. This study grouped patients with prediabetes with those who developed gestational diabetes in the late second trimester. These two groups may be intrinsically different and may require a different treatment approach. A study evaluating the differences between these two groups and how they respond to treatment may result in a smaller proportion of LGA neonates and possibly even cesarean deliveries.
In summary, in this study, the IADPSG screening method for gestational diabetes was not associated with a reduction in LGA newborns or cesarean deliveries but was associated with a higher rate of gestational diabetes.
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