obg

1. Brow presentation
Associate Professor
MSc.N OBG

8. • Brow is the rarest variety of cephalic presentation
where the presenting part is the brow and the
attitude of the head is short that of degree of
extension necessary to produce face
presentation, i.e. the head lies in between full
flexion and full extension.
• The denominator is the fore head (frontum: Fr).

9. INCIDENCE:
• The incidence of brow is very rare, about 1 in 1,000
births.
• However, it may persist temporarily while a deflexed
head tends to become extended to produce a face
presentation.
• This happens especially in flat pelvis where the
biparietal diameter is held in the sacrocotyloid diameter

10. CAUSES:
• The causes of persistent brow are more or less
the same as those of face presentation.
• The position is commonly unstable and
converts to either vertex or face presentation.

11. DIAGNOSIS:
• Antenatal diagnosis is rarely made.
• The findings are more or less like those of face
presentation.
• The cephalic prominence and the groove between
it and the back are less prominent
• The head feels very big and is nonengaged.

12. Vaginal examination:
• The position is to be confirmed on vaginal examination by
palpating supraorbital ridges and anterior fontanel.
• If the anterior fontanel is on mother’s left, with the sagittal suture
in transverse pelvic diameter, it is left frontum transverse
position.
• In late labor, the landmarks may be obscured by caput
formation.
Sonography is confirmatory and also helps in excluding bony
congenital malformation of the fetus

13. MECHANISM OF LABOR:
• Diameter of engagement is through the
oblique diameter with the brow anterior or
posterior.
• As the engaging diameter of the head is
mentovertical (14 cm), there is no mechanism
of labor in an average size baby with normal
pelvis.
• However, if the baby is small and the pelvis is
roomy with good uterine contractions, delivery
can occur in mentoanterior brow position.
• The brow descends until it touches the pelvic
floor.

14. • Internal rotation and descent occur till the
root of the nose hinges under the
symphysis pubis.
• The brow and the vertex are delivered by
flexion followed by extension to deliver the
face.
• The mechanism is more or less the same
as face-to-pubis delivery.
• Usual restitution and external rotation
occur.
• There is no mechanism in posterior brow
position.