Gaya APA

Spong, C, Y. et al (2010). WILLIAMS OBSTETRICS 23RD EDITION (23rd edition). United states of America: McGraw-Hill Book Company.

Gaya MLA

Spong, Catherine, Y.. et al. "WILLIAMS OBSTETRICS 23RD EDITION". 23rd edition United states of America: McGraw-Hill Book Company, 2010. Text.