In this new study from American sociology's flagship journal American Sociological Review, self-assessment of overall health of women at age 40 is significantly higher if they had no children out of wedlock. Single mothers experience higher levels of stress, psychological distress, and social isolation. According to the authors, Hispanic women escape the negative effects because their cohabiting more closely resembles marriage, and they have closer kinship networks. Overall, cohabiting or getting married after the nonmarital birth does not mitigate the negative effects. Only an enduring marriage to the biological father improves health. (They adjust for selection effects.)
By the way, it puts a smile on my face to see IQ as a control: not surprisingly, it predicts better overall health.