APA (7th ed.) Citation

Hibbard, B. M., Rosen, M., & Gray, O. P. (1988). Principles of obstetrics. Butterworths.

Chicago Style (17th ed.) Citation

Hibbard, Bryan M., Michael Rosen, and Oliver Peter Gray. Principles of Obstetrics. London: Butterworths, 1988.

MLA (9th ed.) Citation

Hibbard, Bryan M., et al. Principles of Obstetrics. Butterworths, 1988.