The diameter of fetal head, which comes in totally deflexed head :
Circumferences of the head in different attitudes: -- Complete flexion Biparietal-suboccipito-bregmatic. Shape -- almost round 27.5 cm (11") -- Deflexed Biparietal-occipito-frontal. Shape -- oval 34 cm (13 1/2 ") -- Incomplete extension Biparietal-mento-veical. Shape -- bigger oval 37.5 cm (15") -- Complete extension Biparietal-submento-bregmatic. Shape -- almost round 27.5 cm (11") Reference: D C Dutta Textbook of Obstetrics 7th edition,page 85.
Suboccipito-frontal
Occipito-frontal
Submento-bregmatic
Suboccipito-bregmatic
General obstetrics