Vitamin A is fat soluble vitamin that is stored in the liver and used when required. It can be in preformed that is form which is directly use by our body. Preformed vitamin A is obtained from non vegetarian diet by consuming the liver, meat, eggs, dairy products and by supplements. Other way to get vitamin A is by eating vegetables and fruits that contain carotene. But this is not preformed means our body convert beta carotene to useable vitamin A. The vegetarian source are carrots, sweet potatoes, spinach, broccoli, lettuce, etc.
Vitamin A is necessary for vision and also for growth and development of baby during pregnancy. But it does not mean that being pregnant or while planning to get pregnant mother should take it without considering how much of it she is taking on daily basis because since it is fat soluble and hence too much of it can be dangerous.
Vitamin A requirement for pregnant woman is 770 microgram or 2565 IU and for breastfeeding mother it is 1330 microgram or 4330 IU. For mother to be it is necessary that when taking supplements she read the labels and calculate how much vitamin A is in her daily diet.
Also when having good diet she would also getting it from her food. Some topical creams also contain it which may get into blood stream from pores on skin. So she gets vitamin a from many sources.
Therefore she should be careful that in any case the amount of daily vitamin A consumption not to exceed 10,000 IU because in studies it is observed that it may result into birth defects in developing baby.
So be careful while taking vitamin supplements and if have any doubt clear that by discussing that with your gynaecologist.