Gupta, S., Seth, A.K., Gupta, A., and A.G. Gavane. Transplacental passage of fluorides. J Pediatr. 1993 Jul;123(1):139-41.
Transplacental passage of fluorides was studied in 25 randomly selected neonates. Blood samples collected simultaneously from the mother and the umbilical cord showed that average fluoride concentration in the cord blood was 60% of that in mother’s blood. When concentration in the mother’s blood exceeded 0.4 ppm, the placenta acted as a selective barrier.