Up to 90% of first time mothers will have stretch marks. They usually first appear in the late second and early third trimester, however one study showed that 43% of women actually develop them before the 24 week mark.
Diaper rash is thought to occur in up to 1/3 of newborns, and typically develops between the 9th and 12th month of life. In fact, it is the most common skin condition in infancy and a top reason for a trip to the pediatrician!
Eczema reduces quality of life by a lot, leads to missed school days, and costs parents and the healthcare system billions of dollars each year. There is also some controversial evidence that it can affect the mental development of a child.