This article describes testosterone concentration change throughout pregnancy and the remarkable high testosterone concentration in pregnancy among women with preterm delivery, although a question of mechanisms involving the testosterone arise remains. Control serum testosterone increased up to the third trimester. In four pregnancies of three cases that presented premature labor, testosterone concentrations rose to 8 to 18 times the control group’s concentration that remained within 89 ± 41 ng/dl before delivery. In the setting of over-threshold level of testosterone within altered fetoplacemtal unit, the production of androstenedion and estrogens at the level of the amnion and deciduas may proceed by alternative mechanisms to spontaneous parturition.  Despite this low frequency, we consider that testosterone screening is generally warrant in all women with unexplained premature labor.