Research carried out at Sains University in 2018 assessed the effects of propolis alone or combined with insulin on maternal status, pregnancy outcomes, and placental oxidative stress in diabetic rats. The experimental design included forty female rats randomly assigned into five groups; non-diabetic, diabetic, diabetic given propolis, diabetic given insulin, and diabetic given insulin and propolis groups. Propolis and insulin were administered at 300 mg/kg/day orally and 5.0 IU/kg/day subcutaneously, respectively, for four weeks. The results demonstrated significant improvements in fasting blood glucose, conception period, implantation losses, and placental oxidative stress markers of groups treated with propolis and also with propolis and insulin.
The scientists proposed a regular propolis intake during pregnancy.

Reference: Usman, UZ et al. "Propolis improves pregnancy outcomes and placental oxidative stress status in streptozotocin-induced diabetic rats." BMC Complementary and Alternative Medicine 18.1 (2018): 324.