Should mothers of newborns let their babies cry it out or rush to their comfort? A study on 1200 infants sleeping patterns was tracked over 36 months. They found that by age 6 months that 2/3 of infants slept through the night. Of the 1/3 that did not, by 15 months they awakened twice a week, and by 15 months only once a week. If sleeping problems last more than 15 months it was recommended they see their pediatrician to look for possible health issues.
Infants of mothers who were depressed during their pregnancy and those on SSRI antidepressants were prone to more severe sleeping problems.