Mechanism of Normal Labour

Summary

This video script explains the process of normal labor for a baby in the right occipital anterior (ROA) position. It details how the fetal head enters the maternal pelvis, flexes under uterine pressure, and descends. The script highlights the 1/8 rotation of the fetal head, the misalignment of shoulders, and the subsequent realigning and crowning. It concludes with the birth of the baby through lateral flexion, illustrating the mechanism of normal labor.

Takeaways

• 🤰 The mother is in a supine position with the fetus entering the pelvis in the right occipital anterior (ROA) position.
• 👶 The fetal head enters the maternal pelvis with the sagittal suture aligned with the transverse diameter of the pelvis.
• 📉 Fetal axis pressure from uterine contractions causes the fetal head to flex, presenting the smallest diameter, the suboccipital-pubic diameter.
• 🔄 As labor progresses, the fetal head descends through the pelvis, causing the occiput to rotate anteriorly by 1/8.
• 🚫 The shoulders do not rotate by the same 1/8, leading to a misalignment between the fetal shoulders and the head.
• 🛑 The fetal head slips beneath the suprapubic arch, allowing for crowning to occur.
• 🔃 Restitution is the realigning of the fetal head and shoulders after the 1/8 rotation.
• 💪 The anterior shoulder meets resistance and rotates anteriorly 1/8, followed by the posterior shoulder slipping into the curve of the sacrum.
• 👶🌀 Lateral flexion of the fetus facilitates birth, with the baby being born through this mechanism.
• 📚 This video script outlines the mechanism of normal labor for a baby in the ROA position.

Q & A

What is the initial position of the fetus as it enters the pelvis?

The fetus enters the pelvis in the right occipital anterior (ROA) position.

How does the fetal head align with the maternal pelvis at the beginning of labor?

The fetal head enters the inlet of the maternal pelvis with the sagittal suture in the transverse diameter of the maternal pelvis.

What is fetal axis pressure and how does it affect the fetal head?

Fetal axis pressure is the pressure from uterine contractions on the fetal sacrum, causing the baby's head to flex and present the smallest diameter, the suboccipital-pubic diameter.

What is the significance of the fetal head flexing during labor?

Fetal head flexing allows the smallest diameter of the head to pass through the maternal pelvis, facilitating descent.

What happens when the occiput meets the resistance of the maternal pelvic floor?

The fetal occiput rotates anteriorly by 1/8 due to the shape of the maternal pelvic floor.

Why is it important to note that the shoulders do not rotate through the same 1/8 as the fetal head?

The lack of shoulder rotation through the same 1/8 as the head results in misalignment between the fetal shoulders and head, which is a crucial aspect of the labor mechanism.

What is the process called when the fetal head pivots on the sub-occipital region during crowning?

The process is called restitution, where the fetal head and shoulders realign after the 1/8 rotation.

How does the fetal head move to achieve restitution during labor?

The fetal head extends, releasing the syncsoput, face, and chin, which sweep the perineum to realign the head and shoulders.

What is the significance of the anterior shoulder meeting the resistance of the pelvic floor?

The anterior shoulder rotates anteriorly 1/8, allowing the fetus to descend further and prepare for birth.

How does the baby achieve lateral flexion during birth?

The baby is born by lateral flexion as the anterior shoulder sweeps under the pubic arch and the posterior shoulder slips into the curve of the sacrum.

What is the final position of the baby as it is born, according to the mechanism of normal labor described?

The baby is born with lateral flexion, completing the mechanism of normal labor for a baby in the ROA position.