Brow presentation constitutes an absolute foeto-pelvic disproportion, and vaginal delivery is impossible (except with preterm birth or extremely low birth weight).
This is an obstetric emergency, because labour is obstructed and there is a risk of uterine rupture and foetal distress.
– Head is high; as with a face presentation, there is a cleft between the head and back, but it is less marked.
– On vaginal examination the brow, orbits, anterior fontanelle and, occasionally, the eyes and bridge of the nose are palpable (Figures 7.9). But it is not possible to palpate:
• the chin (it is not a face presentation),
• the posterior fontanelle (it is not a vertex presentation).
Figures 7.9 - Brow presentation
Any mobile presenting part can subsequently flex. The diagnosis of brow presentation is, therefore, not made until after the membranes have ruptured and the head has begun to engage in a fixed presentation. Some brow presentations will spontaneously convert to a vertex or, more rarely, a face presentation.
During delivery, the presenting part is slow to descend: the brow is becoming impacted.
– Perform a caesarean section. When performing the caesarean section, an assistant must be ready to free the head by pushing it upward with a hand in the vagina.
– As a last resort, if caesarean section is impossible, attempt two manoeuvres:
• Convert the brow presentation to a face presentation: between contractions, insert the fingers through the cervix and move the head, encouraging extension (Figures 7.10).
• Attempt internal podalic version (Section 7.9).
Both these manoeuvres pose a significant risk of uterine rupture. Vacuum extraction, forceps and symphysiotomy are contra-indicated.
Figures 7.10 - Manoeuvre to convert brow to face presentation
Perform an embryotomy if the cervix is sufficiently dilated (Chapter 9, Section 9.7) otherwise, a caesarean section.