Response to Comment on Ooi and Wong. Twin Pregnancy With Gestational Diabetes Mellitus: A Double Whammy? Diabetes Care 2018;41:e15–e16

We appreciate the interest and comments from McGrath et al. (1) relating to our recent article (2). Although singleton pregnancies complicated by gestational diabetes mellitus (GDM) and non-GDM twin pregnancies had been extensively studied, evidence on how GDM twin pregnancies should be optimally managed is still lacking.

We concur with McGrath et al. (1) that the current approach in managing women with GDM twin pregnancies may not confer harm and the risk of macrosomia is very low. However, the concern is more on the risk of small-for-gestational-age (SGA) babies (birth weight below 10th percentile). Although our rate of SGA babies for our GDM twins was not different from that of babies born from non-GDM twin pregnancies, the risk was significantly higher than that for GDM singletons (23.2% vs. 13.6%, P < 0.001) (2). There is some suggestion that GDM twin pregnancies could be overtreated. Guillén et al. (3) suggested that mild maternal hyperglycemia could be beneficial for twin pregnancies due to increased metabolic demands (3), and hence the current glucose targets for GDM may not be appropriate for twin pregnancies. A small study on GDM twin pregnancies referenced by McGrath et al. raised the concern that women with better glycemic control were more likely to have SGA babies (4). It is possible that medical nutritional therapy recommended for singleton pregnancies may not provide adequate caloric requirement for twin pregnancies. Tighter glycemic control was also not associated with a lower rate of preeclampsia in that study (4).

Because the prevalence of twin pregnancy is low (1.5% of all pregnancies in Australia), most of the studies on twin GDM pregnancies had small sample sizes and were underpowered to adequately evaluate pregnancy outcomes. We agree with McGrath et al. (1) that a multicenter prospective study would be necessary to properly evaluate the appropriate glucose targets and the nutritional needs for this group of women. The goals of therapy for women with twin GDM pregnancies would need to be better defined.