APA

Heath V. C., Southall T. R., Souka A. P., Novakov A. & Nicolaides K. H. (19990121). Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history. : Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology.

Chicago

Heath V C, Southall T R, Souka A P, Novakov A and Nicolaides K H. 19990121. Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history. : Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology.

Harvard

Heath V. C., Southall T. R., Souka A. P., Novakov A. and Nicolaides K. H. (19990121). Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history. : Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology.

MLA

Heath V C, Southall T R, Souka A P, Novakov A and Nicolaides K H. Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history. : Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 19990121.