Those of the Romans who write natural history say that when seed is cast into the womb, on the third day it is transformed into blood and "paints" [Gk. διαζωγραφεῖν] the heart, which is said to be formed first and to die last. For if three is the beginning / ruling principle of numbers, and is an odd number, then consequently the beginning / ruling principle of birth [comes] from it. And on the ninth [day], it congeals and coagulates to form flesh and marrow; and on the 40th [day it is said] to be completed as a comprehensive form of configuration—to put it simply, a complete human being. Something similar to [these properties of] the days [holds true] in the case of the months. In the third month, [the fetus] held in the womb begins to move; and in the ninth month it is completely finished and hastens to come out.(John Lydus, De Mensibus, February)
After the pregnancy, they say that the newborn child is wrapped in swaddling clothes on the third [day], and that on the ninth [day] it becomes stronger and tolerates being touched; and on the 40th [day] it acquires the ability to laugh and it begins to recognize its mother.
Thanks very much to Roger Pearse for placing this in the public domain.