Pregnancies complicated by preexisting maternal diabetes mellitus are associated with a higher risk of birth defects in infants, known as diabetic embryopathy. The common defects seen in the central nervous system result from failure of neural tube closure. The formation of neural tube defects (NTDs) is associated with excessive programmed cell death (apoptosis) in the neuroepithelium under hyperglycemia induced intracellular stress conditions. The early cellular response to hyperglycemia remains to be identified. We hypothesize that hyperglycemia may disturb intracellular calcium (Ca2+) homeostasis, which perturbs organelle function and apoptotic regulation, resulting in increased apoptosis and embryonic NTDs. In an animal model of diabetic embryopathy, we performed Ca2+ imaging and observed significant increases in intracellular Ca2+ ([Ca2+](i)) in the embryonic neural epithelium. Blocking T-type Ca2+ channels with mibefradil, but not L-type with verapamil, significantly blunted the increases in [Ca2+](i), implicating an involvement of channel type-dependent Ca2+ influx in hyperglycemia-perturbed Ca2+ homeostasis. Treatment of diabetic pregnant mice with mibefradil during neurulation significantly reduced NTD rates in the embryos. This effect was associated with decreases in apoptosis, alleviation of endoplasmic reticulum stress, and increases of anti-apoptotic factors. Taken together, our data suggest an important role of Ca2+ influx in hyperglycemia-induced NTDs and of T-type Ca2+ channels as a potential target to prevent birth defects in diabetic pregnancies. (C) 2019 Elsevier Inc. All rights reserved.