Some Vitamin A, like calcium, Vitamin D, magnesium and Vitamin K, is necessary for healthy bones, but regular overdosing on the amount of vitamin A consumption has been associated with adverse skeletal effects.
Vitamin A in large doses is believed to inhibit osteoblasts, which are the cells that actually form new bone by laying the matrix of bone down. Overdosing on Vitamin A can also interfere with vitamin D activity and thus could inhibit proper calcium absorption, and stimulate osteoblast bone cells, which wear bone away in the normal process of remodeling. The net effect is increased bone resorption for a net thinning of bone and an increased fracture risk.
Be sure the amounts of vitamin A, retinol, and beta-carotene do not exceed the recommended doses. Remember that not all vitamin and mineral supplements have been through the intense approval process that drugs have, and you do have to be careful with what sources of vitamins you consume as well. And check with your gyno on your overall nutrition status and what she would like you to take after calculating what you have in your typical daily food intake.