A parturient woman is 23 years old. Vaginal obstetric examination reveals full cervical dilatation. There is no fetal bladder. Fetal head is in the plane of pelvic outlet. Sagittal suture is in mesati-pellic pelvis, anterior fontanel is closer to pubes. The fetal head diameter in such presentation will be:

Answer options

1. Fronto-occipitalis recta
2. Biparietal
3. Suboccipitio-frontalis
4. Mento-occipitalis
5. Suboccipito-bregmaticus

Explanation

Suboccipitobregmatic diameter = the diameter of the fetal head from the lowest posterior point of the occipital bone to the center of the anterior fontanelle; this is typically the smallest diameter and is the one that presents, optimally, in labor.