Blood alcohol concentration: a critical factor for producing fetal alcohol effects.

A dose of 6.6 g/kg of alcohol, delivered in 12 equally-spaced fractions each 24 hours via an artificial rearing procedure during postnatal days 4-10, produced mean blood alcohol concentrations (BACs) that were low (46.6 mg/dl), but stable with time. This relatively constant alcohol exposure did not limit brain growth in neonatal rats when measured on postnatal day 10. The same daily dose concentrated into 6 fractions over 12 hours (with 6 alcohol-free fractions the remaining 12 hours) resulted in cyclic BACs having high peaks (270.2 mg/dl). The cyclic regimen produced a significant reduction in brain growth. Thus, the peak blood alcohol concentration is a critical factor in determining the minimum dose for producing microencephaly and must be considered when estimating the relative teratogenic risks of alcohol intake during pregnancy.