The shoest diameter of fetal head is :
Biparietal diameter
Suboccipito frontal diameter
Occipito frontal diameter
Bitemoral diameter
Fetal head diameters Largest transverse diameter is biparietal diameter measuring approximately 9.5cms Shoest transverse diameter is bitemporal diameter measuring approximately 8cms Reference: William's Obstetrics; 24th Edition; Chapter 5 The transverse diameters of fetal skull which are concerned with the mechanism of labor are -- Biparietal diameter--9.5 cm (3 3/4 ''): It extends between two parietal eminences. Whatever may be the position of the head, this diameter nearly always engages. -- Super-subparietal--8.5 cm (3 1/2 ''): It extends from a point placed below one parietal eminence to a point placed above the other parietal eminence of the opposite side. -- Bitemporal diameter--8 cm (3 1/4 ''): It is the distance between the anteroinferior ends of the coronal suture. -- Bimastoid diameter -- 7.5 cm (3''): It is the distance between the tips of the mastoid processes. The diameter is incompressible and it is impossible to reduce the length of the bimastoid diameter by obstetrical operation. reference: D C Dutta Textbook of Obstetrics 7th edition page 85
General obstetrics