Teratogenicity of vitamin A was firstly detected in experimental animals in 
1953. Nearly 30 years later, teratogenicity of vitamin A analogue-isotretinoin 
was reported in humans. Isotretinoin induces serious birth defects of 
craniofacial and central nervous system, cardiovascular system and thymic 
malformations--in about 25% of babies exposed during the first trimester of 
their prenatal development. The biological interconversion of isotretinoin to 
vitamin A is known. That is why later epidemiological studies focused on high 
vitamin A intake in pregnant woman: Women who use daily vitamin A supplements 
during early pregnancy have approximately a two-fold increased risk of giving 
birth to a malformed baby. On the basis of these data, replacement of vitamin A 
has been recommended with its natural precursor B-carotene which is supposed to 
be more safe for pregnant woman due to its limited absorption from intestine. 
Aim of the present paper was to test a possible direct embryotoxic effect (i.e. 
lethality + teratogenicity) of B-carotene in chick embryos and to compare these 
results with known embryotoxicity of vitamin A in the same experimental model. 
Single subgerminal or intaamniotic injection of vitamin A or B-carotene within 
day 2-5 of incubation was used for estimation of the beginning of the 
embryotoxicity range determining the minimal embryotoxic doses. Vitamin A 
started to affect development between doses 0.3-0.3 microm [corrected] per 
embryo. Malformations of head, extremities and heart were detected similarly 
like in laboratory mammals and in man. B-carotene exhibited such an effect 
neither after injection of the highest tested doses-100 microm [corrected] per 
embryo. The results documented the strong difference in embryotoxicity between 
vitamin A and B-carotene. After theoretical extrapolation of the results 
achieved in the chick embryo, the minimal embryotoxic doses of vitamin A in 
mammals were estimated to be between 0.1-1 mg/kg of maternal weight and those of 
B-carotene to be more than 1000 mg/kg of maternal weight. Human epidemiological 
studies have proved teratogenicity of vitamin A after daily doses 25,000 
i.u.-8.3 mg (0.13 mg/kg)- and reduction of its maximum intake has been 
recommended to 10,000 i.u. per day (0.05 mg/kg). The results about 
teratogenicity of vitamin A achieved in the chick embryo are in agreement with 
such a recommendation. Intake of vitamin A in the food is sufficient for 
pregnant woman in common Czech population. Therefore, an artificial 
supplementation of vitamin A brings risk of overdosage. If supplementation by 
vitamin A is unavoidable during pregnancy, B-carotene should be preferred.