Beta carotene vs Retinol
Vitamin A is sourced from Retinol (preformed) or Carotene (provitamin A) in foods.
The recommended Vit A during pregnancy is 1000 RE (retinol equivalents)/day 
=3,300 IU (1000 micro gram) as retinol or
=19,800 IU (6000 micro gram) as beta carotene 
this is the combined amount; food + supplemental forms.
Pregnant women 19 years old or older should not consume more than 3,000 microgram RAE a day. This is 10,000 international units.
The average American diet contains 7,000-8,000 IU of Vit A derived from different sources.
The risk of birth defects owing to excess vitamin A (25,000 IU) in the form of retinol has been documented.
Beta carotene has not been associated with toxicity and is therefore the recommended source of vitamin A for women in their reproductive years.
(for food sources containing retinol click here)
(for food sources containing beta carotene click here)
Ensure the vitamin A in your prenatal vitamins (if containing Vitamin A) is in the form of beta carotene an not retinol.
 Teratology society position paper: Recommendations for Vit A use during pregnancy.