Which of the following trace element cannot be completely supplemented by diet in pregnancy –

The demand of iron during pregnancy is markedly increased. This is mostly limited to the second half of pregnancy specially to the last 12 weeks. An adequate balanced diet provides about 18 - 20 mg of iron. The amount of iron absorbed from the diet and that mobilized from the store are inadequate to meet the demand. Note that this is so despite the fact that absorption of iron through the gut is enhanced during pregnancy. This also explains the need for iron supplementation and also why it is limited mostly to the second half.