We study the determinants of season of birth, for white married women aged 20-45 in the US, using birth certificate and Census data. We also elicit the willingness to pay for season of birth through discrete choice experiments implemented on the Amazon Mechanical Turk platform. We document that the probability of a spring first birth is significantly related to mother's age, education, smoking status during pregnancy, and the mother working in "education, training, and library" occupations, whereas a summer first birth does not depend on socio-demographic characteristics. We find consistent but stronger correlates when focusing on second births, while all our findings are muted among unmarried women. We estimate the average willingness to pay for a spring birth to be 600 USD, which is about 18% of the most valued birth in our Amazon Mechanical Turk experimental sample or 15% of the mean charges for a normal birth in 2013 according to the Agency for Healthcare Research and Quality.