Impact of hyperglycemia on early embryo development and embryopathy: in vitro experiments using a mouse model

The aim of this study is to model the processes of early embryopathy seen in human pregnancy complicated by maternal hyperglycemia secondary to maternal diabetes using a mouse embryo culture system.

Female mice were superovulated and mated in pairs. Two-cell embryos were harvested from the oviducts and cultured in vitro in KSOM medium (synthetic oviductal medium enriched with potassium) supplemented with 0.2, 5.56, 15.56 or 25.56 mM d-glucose. Cell proliferation, differentiation and apoptosis were assessed. Experiments were performed in constant, embryos exposed to a particular concentration of glucose (0.2, 5.56, 15.56 or 25.56 mM) from harvest to either Day 5 post fertilization (pf) or Day 8 pf, and fluctuating, embryos exposed to alternate high 25.56 mM and normal 5.56 mM concentrations of glucose between harvest and Day 5 pf, glycemic culture.

Expected levels of blastocyst formation and hatching were seen at 0.2 and 5.56 mM concentrations of glucose but both were impaired at higher concentrations (chi(2), P < 0.005; P < 0.001). Total cell numbers (P < 0.002) and cell allocation to the inner cell mass (P < 0.01) were reduced, but with no evidence of enhanced apoptosis in the hyperglycemic cultures. Variation in hyperglycemic exposure of the embryos on Days 2, 3 and 4 showed no adverse effects of hyperglycemia up to 24 h, but 48 and 72 h exposures were equally embryopathic (P < 0.01).

Hyperglycemic exposure for >24 h is toxic to early embryo development. These findings may explain the lower than expected implantation rates and higher than expected rates of congenital abnormality and early pregnancy loss seen in patients with diabetes, particularly those with poor diabetic control.