Lee, K. A., & Gay, C. L., Sleep in late pregnancy predicts length of labor and type of delivery. American journal of obstetrics and gynecology, 191(6), 2041-2046, 2004.
Chang, J. J., Pien, G. W., Duntley S. P., & Macones, G. A. Sleep deprivation during pregnancy and maternal and fetal outcomes: is there a relationship? Sleep medicine reviews, 14(2), 107-114, 2010.