Brow presentation.pptx

obg

1. Brow presentation Associate Professor MSc.N OBG

2. 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).

3. 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

4. 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.

5. 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.

6. 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

7. 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.

8. 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.