From Creatures Wiki
Pregnancy is the process that female creatures go through in order to produce new creatures.
The process begins with a kiss-pop which may or may not result in pregnancy - as in humans and other mammals, whether or not pregnancy occurs is dependent on if the female is fertile at the time. To make this easier on the Hand, female Norns at least generally only become friendly when they are fertile, and tend to slap males away if advances are attempted at any other point in their cycle.Norn pregnancy lasts for one to two minutes and results in the laying of an egg. To do this, the female will squat down and raise her head upwards, with her hands on her cheeks (see the image). She will usually go to sleep after laying, as it is very tiring work!
Pregnancy can be induced in Norns by COBs and Agents such as the Inseminator and DDNA Bank. There is also an occasional mutation where a female will not be able to lay her egg (this can also be caused by inseminating an infertile Norn). When this occurs, a COB or Agent must be used to get the egg out.
If a female creature is exposed to radiation while pregnant, there is a higher chance of her offspring mutating.