Does single pregnancy adversely affect infant health? This is a challenging research question because there is selection in coresidence during pregnancy. We exploit quasi-natural variation in single pregnancy from the moment of conception to birth, arising from the reform of the marriageable age laws in Korea. The Korean birth certificate data are unique. They provide the information about the coresidence status in addition to the legal marital status. The coresidence start date allows us to identify the intensity of coresidence during pregnancy. We find that coresidence or legal marriage during pregnancy does not significantly affect birth outcomes.
