Delayed elimination of caffeine by women in the last 2 weeks of pregnancy.

Caffeine elimination was studied in 15 women at 38 to 40 weeks' gestation. The mean hourly caffeine clearance, 37 ml/kg, determined from assays of saliva, was only 39% of the value previously reported for nonpregnant adults (94 ml/kg). Reassessment in four of the women 2 to 12 weeks post partum showed that in each woman the caffeine clearance had increased more than threefold and that the mean caffeine concentration in the saliva after no intake of caffeine for 24 hours was now much lower (0.07 v. 0.84 microgram/ml).