This website discusses it thus:
The number forty has long been universally recognized as an important number, both on account of the frequency of its occurrence, and the uniformity of its association with a period of probation, trial, and chastisement. It is the product of 5 and 8, and points to the action of grace (5), leading to and ending in revival and renewal (8). This is certainly the case where Forty relates to a period of evident probation. But where it relates to enlarged dominion, or to renewed or extended rule, then it does so in virtue of its factors 4 and 10, and in harmony with their signification.If that doesn't sum up pregnancy, I don't know what does! Chastisement (not punishment, but testing your limits), trial, probation, followed by revival, renewal and enlarged dominion. Think about it- all over the scripture the number 40 signifies a trial followed by a transformation:
-Noah's flood rains lasted 40 days and 40 nights before the earth was clean
-Moses was in Egypt 40 years before becoming sympathatic to the israelites, Midian for 40 years before becoming a prophet, and on the mountain for 40 days before receiving the Stone Tablets
-The Children of Israel wandered 40 years in the wilderness before entering the promised land
-Elijah fasted/repented in the wilderness for 40 days before the Lord sent him forth as a prophet again
-Jesus fasted in the wilderness for 40 days before beginning his earthly ministry
-Jesus tarried with his disciples after his resurrection before ascending to heaven
And now, for Forty Weeks, I will be tested, tried, and chastised. And at the end, there will be a new life, and I will be transformed and renewed.
Anyways, I thought that was fun to think about.