Changes in blood progesterone concentration during pregnancy in the lizard Tiliqua (Trachydosaurus) rugosa

Progesterone concentrations during pregnancy were measured in the plasma of the viviparous lizard (scincid) Tiliqua (Trachydosaurus) rugosa, using a radioimmunoassay specific for progesterone. The length of gestation in this Australian lizard was 140-170 days. The average number of young was 2.8 and the mean neonatal weight 58 g (maternal body weight 500-700 g). The mean concentration of progesterone was greatest (7.2 nmol/l) during the second trimester of pregnancy; mean values during the first and third trimesters, and in non-pregnant females, were 1.8, 0.9 and 0.2 nmol/l respectively.