Your baby's skeleton began forming at the end of the first trimester, but the majority of your calcium is transferred to the baby from your body in the third trimester. This happens regardless of your calcium intake. If a mother-to-be's diet is low in calcium, it will be taken from the reservoir in her bones, which can affect her bone density.
The recommended amount of calcium in pregnancy is 1000 mg daily. Calcium needs to be accompanied by vitamin D in order to be absorbed by the body.
Dairy products are a rich source of calcium, and some, such as margarine and low-fat spreads, are often fortified with vitamin D. Vegetarian sources of calcium include tofu, leafy green vegetables, dried fruit, seeds, and nuts.