Eastern Diamondback Rattlesnakes breed in the fall and spring, ovulate in the spring, gestate over the course of four to six months, and give live birth in the late summer and early fall. Most litters average 12-21 in number. The snakes are 12 to 15 inches long when born and are fully capable of delivering a deadly bite.
Males are thought to follow pheromones emitted by the female. Males move most often in the late summer and early fall during breeding season.
Most wild caught females that drop babies are large snakes, over 4 feet. (source DH)
In captivity the introduction of a second male to a pair will often induce breeding (source MS)