A Finnish research study by Hypponen and colleagues followed children up for 31 years from 1966 to 1997. In those who were given 2000iu of colecaciferol (vitamin D3) in early life there was an 80% reduction in the incidence of type 1 diabetes.
Women who are having children in their 30’s have been told by health professionals virtually all their lives to avoid the sun and therefore not produce the vitamin naturally through exposure of the skin. The further north you live the less ability there is to get the correct UVB wavelength for vitamin D production. Many will be deficient in vitamin D throughout the pregnancy. The UK government has suggested a dose of 400iu. I believe that is too low.
The Canadian Paediatric Authoroties suggest 2000iu in pregnancy and breastfeeding