How does diabetes cause birth defects?

Metabolism: Diabetes is not a simple disease. It wrecks energy metabollism and has an effect on all our cells. During pregnancy this can affect the fetus since mom feeds baby and the excess sugar has its effect in both mom and baby. That is why good control is essential.

Oxidative stress.: Uncontrolled diabetes mellitus at the time of conception and the first trimester showers the conceptus with free oxygen radicals (excess oxidative stress). This usually has an all-or-nothing effect <5 weeks (meaning miscarriage vs, no effect at all), however at later gestational age (6-10 weeks) it can cause several anatomical defects such as vsd, caudal regression, spinal defects etc.