Cardinal Movements of Labor: A Guide to Understanding Fetal Positioning and Progression

During labor, the fetus undergoes a series of movements that help it progress through the birth canal and eventually emerge into the world. These cardinal movements are crucial for a successful delivery and can have a significant impact on the outcome of childbirth. In this article, we will explore the key events that take place during labor and how they relate to fetal positioning.

The Anterior Shoulder: A Key Player in Labor

The anterior shoulder is wedged under the symphysis pubis at the level of the acromion, playing a crucial role in the early stages of labor. As the posterior shoulder pushes the coccyx backwards and is expelled, the anterior shoulder follows suit. This movement helps to flex the fetal back and prepare it for its journey through the birth canal.

Flexion and Rotation: The Next Steps

As the fetus moves down the birth canal, it undergoes a series of flexions and rotations that help it progress towards delivery. The biacromial diameter becomes anteroposterior as the fetal back points to the maternal right or left side, while the upper limbs are forced into flexion. This shortens the biacromial diameter and allows the fetus to assume an oblique position.

The Expulsion of the Lower Limbs

In complete breech presentation, the lower limbs are usually expelled at the same time as the buttocks. The posterior buttock pushes the coccyx backwards, distends the perineum, and then becomes exteriorized, fully releasing the anterior buttock. This movement allows the anterior buttock to descend under the pubic bone and begin opening the vulvar orifice.

Rotation and Asynclitism: Important Considerations

The cardinal movements of labor are not without their challenges. In anterior positions, a 45-degree backward rotation occurs, while in posterior positions, a 45-degree forward rotation takes place. Additionally, bitrochanteric diameter descends obliquely with slight posterior asynclitisim, which can impact the progression of labor.

Engagement and Internal Rotation: The Final Stages

Engagement usually occurs in an oblique position, with the sacrum rotated internally (ie, within the birth canal) by 45 degrees. This internal rotation allows the fetus to progress through the birth canal more easily and prepares it for delivery.

In conclusion, the cardinal movements of labor are a complex series of events that help the fetus navigate its journey from the womb to the outside world. Understanding these movements is crucial for healthcare providers and new mothers alike, as they play a critical role in ensuring a safe and successful delivery. By recognizing the key events that take place during labor, we can better support women and their babies throughout this transformative process.

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