Preterm delivery commonly causes neonatal morbidities and mortality. Prematurely born neonates are susceptible to various serious medical complications both early and later in life, including respiratory distress, bronchopulmonary dysplasia, pneumothorax, pneumonia, sepsis, patent ductus arteriosus, necrotizing enterocolitis, intraventricular hemorrhage and cerebral palsy. [1–3] Therefore, understanding the nature of the condition and associated risks might help in better prevention of preterm delivery and improving pregnancy outcomes.
While mean GA at delivery was comparable between the 2 groups, incidence of spontaneous preterm delivery in this study was significantly higher in GDM comparing to non-GDM group (15.8% vs. 7.1%, p = 0.004) and multivariate analysis showed that GDM independently increased the risk of preterm birth by 2.15 times (95% CI 1.20–3.84). The findings were similar to other previous studies. [9–11] Another study showed similar risk of preterm birth between those with and without GDM. [13] Variations in the results between studies might partly due to differences in population characteristics, GDM screening and risks, risks of preterm and associated management scheme. Some previous studies also reported increased risk of preterm delivery as well as other adverse outcomes among GDM that was detected early in pregnancy, despite treatment. [14, 15] This could possibly be related to the higher severity of hyperglycemia among this specific group of women. Higher risk of preterm birth was also observed in women with insulin-treated GDM than those with diet-treated GDM in a previous study. [11] However, the number of insulin-treated cases in this study was too small to evaluate such relationship with valid and reliable results that further studies might be needed. The exact mechanism for the observed association was still not known. Further biologic explanations on possible relationship between GDM and spontaneous preterm delivery are to be explored.
Similar to current knowledge and many previous studies [1–3, 16, 17], the results of this study showed that previous preterm birth was the other strong independent associated factor for preterm birth (adjusted OR 2.56). Progesterone has been demonstrated to be effective in decreasing the risk of preterm birth among these at-risk population. [18–20] As of institutional guideline, all women at high risk for preterm delivery were offered progesterone treatment for prevention of preterm birth, either vaginal, oral, or intramuscular route. However, GDM is not currently included as one of the risks for preterm delivery. If, in the future, evidence on association between GDM and preterm birth is documented, administration of progesterone might have some roles in preterm prevention among this group of women.
Other pregnancy outcomes related to GDM were as expected and have been repeatedly reported. [6] Lower gestational weight gain among GDM has been consistently reported from the same institution. [21, 22] This was probably due to the effect of intensive individual counseling in each GDM woman as well as close monitoring. Increased in LGA as well as macrosomia among GDM was also similar to previous studies. [21–23] Clinical risks associated with GDM were similar to what has been reported from many previous studies, including increasing age and BMI, and previous GDM. [24, 25]
The strength of this study may include diagnosis of GDM was uniform, under the same institutional guideline. Samples were randomly selected from the same population. Selection bias should be minimal as shown by the rate of preterm delivery among non-GDM women was relatively similar to those of other low-risk women in the same hospital. Some limitations should be mentioned. Data were from a tertiary care hospital that generalizability of the results might be limited. In addition, there were variations on GDM screening strategy as well as preterm management between settings that the results might not be applicable. There were too small number of cases in some subgroup of GDM (insulin-treated group or early GDM group) to further evaluate the differences in rates of preterm births with valid and reliable results.
Whether GDM and preterm birth are strongly related needs to be confirmed by future studies. Possible biologic explanations should also be explored. If more strong evidence can be demonstrated in the future, prevention program among this group of women should be developed in order to minimize neonatal morbidities and mortality associated with preterm birth.
In conclusion, women with GDM significantly increased the risk of spontaneous preterm delivery. The other significant risk factor was previous preterm birth. GDM also increased the risk of some adverse outcomes, including LGA, macrosomia, and neonatal hypoglycemia.