The sample initially included 10,459 women, of whom 2,516 (24.1%) met the IADPSG criteria for GDM. We excluded 624 women who received treatment for hyperglycemia in pregnancy per institutional standards (6.0% of the population; 24.8% of all women with IADPSG-defined GDM). The remaining cohort of 9,835 untreated women had a mean age of 28.9 ± 6.0 years; 74.7% were Hispanic, and 31.7% were overweight and 27.8% obese. Of the 1,892 women (19.3%) with IADPSG-defined GDM, 32.9% were also overweight and 43.3% obese. Overall, overweight and obese women were of greater parity, more likely to be Hispanic or black, and had a higher prevalence of GDM than normal-weight women (). Moreover, the average BMI within each BMI group tended to be higher for women with GDM compared with their non-GDM counterparts ().
Maternal characteristics by prepregnancy BMI and GDM status
Although overweight and obese women had, on average, less absolute weight gain during pregnancy than their normal-weight counterparts, they were more likely to exceed the upper limit of weight gain for their BMI recommended by the IOM (22
) (). Mean prepregnancy BMI and absolute gestational weight gain, as well as the proportion of women exceeding weight gain limits set by the IOM, were significantly higher for obese women with GDM compared with their non-GDM counterparts (). Among women who did not develop GDM, those who were overweight had significantly higher mean fasting, 1-h, and 2-h OGTT glucose levels than normal-weight women; those who were obese had significantly higher fasting and 1-h levels than overweight women (). Among women who developed GDM, those who were overweight did not have significantly higher OGTT glucose values than normal-weight women. However, obese women with GDM had significantly higher mean fasting and 1-h glucose than normal-weight women, and significantly higher mean fasting glucose than overweight women with GDM ().
The prevalence of most adverse obstetrical and neonatal outcomes tended to increase with increasing BMI among women with and without GDM (Supplementary Table 1
). Among women without GDM, the proportion of LGA infants born to overweight women was significantly higher than the proportion born to those of normal weight (P
< 0.001) (). Likewise, the prevalence of LGA was higher in infants born to obese women without GDM than to their overweight (P
= 0.050) or normal-weight (P
< 0.001) counterparts (). A similar trend in increasing prevalence of LGA by increasing prepregnancy BMI was observed for women with GDM, with obese GDM women having a significantly higher proportion of LGA infants than either overweight (P
= 0.005) or normal-weight (P
< 0.001) women with GDM (). A similar relationship between increasing prepregnancy BMI and increasing mean ponderal index, for women with and without GDM, was also observed (Supplementary Fig. 1
Prevalence of LGA infants for each prepregnancy BMI/GDM group. White bars, no GDM; black bars, GDM.
The adjusted odds of having an LGA infant increased with increasing BMI among women who did not develop GDM. After controlling for all demographic and clinical confounders, including total gestational weight gain, overweight women without GDM were 1.65 times as likely (95% CI 1.36–2.01), and obese women without GDM were 2.63 times as likely (2.13–3.24), to have an LGA infant as their normal-weight counterparts (). These increases in adjusted odds of having an LGA infant due to overweight and obesity are concomitant with substantial population-attributable risk. Among women without GDM, prepregnancy overweight and obesity each accounted for 8.8 and 12.8% of LGA infants, respectively (). Thus, among women who did not develop GDM, ~21.6% of LGA was attributable to maternal overweight and obesity combined.
AORs and partial PAF for LGA infants
In the absence of overweight or obesity, GDM was associated with higher odds of having an LGA infant. After accounting for demographic and clinical confounders, as well as total gestational weight gain, normal-weight women with GDM were 1.96 times as likely (95% CI 1.43–2.68) to have an LGA infant as their non-GDM counterparts (). Thus, among normal-weight women, those who developed GDM were nearly twice as likely to have an LGA infant as those who did not. However, due to the somewhat small proportion of normal-weight women who develop GDM, only 2.9% of LGA was attributable to GDM among these women.
Women who were overweight or obese prior to pregnancy and developed GDM had substantially higher odds of having an LGA infant than overweight or obese women without GDM, compared with normal-weight, non-GDM women. Overweight women with GDM were 2.77 times as likely (95% CI 2.12–3.63), and obese women with GDM were 5.47 times as likely (4.34–6.90), to have an LGA infant as normal-weight women without GDM (). Among women with GDM, 6.2% of LGA cases were attributable to prepregnancy overweight and 17.1% to obesity. Thus, the combination of being overweight or obese prior to pregnancy and having GDM accounted for ~23.3% of LGA infants ().
To determine the extent to which gestational weight gain may differentially contribute to LGA prevalence among the six groups, we examined the proportion of LGA infants born to women in each of the six prepregnancy BMI/GDM groups per 10 pounds of weight gain (). Within each group, there was a monotonic increasing trend for higher prevalence of LGA with increasing gestational weight gain. The prevalence of LGA was highest for obese women with GDM compared with the other groups of women, at all levels of weight gain (). Although the prevalence of LGA was similar for overweight and normal-weight women with GDM at levels of gestational weight gain <40 pounds, a significantly higher proportion of LGA infants were born to overweight GDM women who gained ≥40 pounds of weight during pregnancy compared with normal-weight women with GDM who gained the same amount (36.8 vs. 22.0%; P = 0.013). Among women without GDM, there were no significant differences in the proportion of LGA infants born to overweight versus normal-weight women, at any level of weight gain. Because overweight and obese women who developed GDM delivered, on average, a few days earlier than women without GDM, we also examined the proportion of LGA with respect to the rate of weight gain (average pounds per week). The trends in average weight gain per week of gestation among the six BMI/GDM groups were similar to those of absolute weight gain shown in (data not shown).
Prevalence of LGA infants among each prepregnancy BMI/GDM group, per 10 pounds of gestational weight gain. White triangles, no GDM; black circles, GDM; solid lines, normal weight; dashed lines, overweight; dotted lines, obese.