Which of the following fetal positions is most favourable for birth/vaginal delivery?
A. Vertex
B. Oblique lie
C. Frank breech presentations
D. Posterior position of the head
Correct Answer: A. Vertex
Explanation
The most favourable fetal position for normal vaginal delivery is:
✅ Occipito-anterior (OA) position
— especially Left Occipito-Anterior (LOA)
🔍 Explanation
- In occipito-anterior position, the occiput (back of fetal head) faces the mother’s anterior pelvis (towards symphysis pubis).
- This allows:
- Maximum flexion of the fetal head
- Engagement with the smallest diameter (suboccipito-bregmatic ≈ 9.5 cm)
- Smooth descent, rotation, and expulsion
🏆 Why LOA is the best
- The left side of the maternal pelvis is usually roomier due to the position of the rectosigmoid colon on the right.
- Uterine contractions are more effective in LOA.
❌ Less favourable positions
- Occipito-posterior (OP)
- Occipito-transverse (OT)
- Face and brow presentations
✔️ Final Answer:
Occipito-anterior position (especially Left Occipito-Anterior – LOA)
Other Options Details
Here is a clear obstetrics-oriented description of each option, focusing on presentation/lie and their relevance to vaginal delivery:
A. Vertex
- Definition: The fetal head is flexed and the occiput (back of the head) presents at the pelvic inlet.
- Presenting part: Vertex (area between the anterior and posterior fontanelles).
- Engaging diameter: Suboccipito-bregmatic (9.5 cm).
- Clinical importance:
✔ Most common and most favourable presentation for normal vaginal delivery.
✔ Allows good moulding and descent through the pelvis.
B. Oblique lie
- Definition: The long axis of the fetus is oblique (diagonal) to the long axis of the uterus.
- Presenting part: Usually shoulder or arm.
- Clinical importance:
✖ Unstable and abnormal lie.
✖ Cannot result in vaginal delivery unless it converts to longitudinal lie.
✖ Risk of cord prolapse if membranes rupture.
C. Frank breech presentation
- Definition: Breech presentation where hips are flexed and knees are extended.
- Presenting part: Buttocks.
- Clinical importance:
✔ Most common type of breech.
✖ Vaginal delivery is possible but risky, especially in primigravida.
✖ Increased risk of head entrapment and birth trauma.
D. Posterior position of the head
- Definition: Occiput of the fetal head is directed towards the maternal sacrum (occipito-posterior).
- Types: Right OP, Left OP, or Direct OP.
- Clinical importance:
✖ Labour is often prolonged and painful.
✖ Increased risk of instrumental delivery or caesarean section.
✔ Some OP positions may rotate to occipito-anterior during labour.
Summary Table
Option Normal/Abnormal Vaginal delivery Vertex Normal Best & easiest Oblique lie Abnormal Not possible Frank breech Abnormal Risky/Selective Posterior head Malposition Difficult
✅ Most favourable option: A. Vertex
I hope that you liked this article.
Thanks!! 🙏 😊
Writer: Vandita Singh, Lucknow (GS India Nursing Group