Adult male and female Sprague–Dawley rats (200 ± 20 g, female: male = 1:1) purchased from the Laboratory Animal Center of Hubei Provincial Center for Disease Control and Prevention were maintained under conditions with an ambient temperature of (24 ± 2) °C and relative humidity of (55 ± 5%) under a 12/12 h light/dark cycle. Clean tap water and basal pellet diet were freely available for rats. After a 7–day observation, animals were randomly divided into four groups with 10 rats in each group: a control group (drinking water with fluorine concentration less than 1.0 mg/L), and three NaF–treated groups. After 2 months of exposure, female and male rats (1:1) in each group were randomly mated overnight. The pregnant rats were housed in separate cages with the same environmental and exposure conditions till the weaning of pups. The female pups were given the same concentration of NaF as their parents did for 6 months after birth