During an uncomplicated spontaneous vaginal delivery, the fetal head must navigate the rigid maternal bony pelvis through a predictable series of biomechanical adaptations. Consider a singleton fetus presenting in the left occipitotransverse position that progresses to a normal delivery. Arrange the following fetal cardinal movements in the correct chronological sequence, starting with the initial entry into the maternal pelvis and ending with the movements immediately following head delivery.
- 1Engagement of the fetal biparietal diameter through the pelvic inlet
- 2Flexion of the fetal cervical spine upon encountering pelvic floor resistance
- 3Internal rotation of the fetal occiput toward the maternal pubic symphysis
- 4Delivery of the fetal vertex via extension under the pubic arch
- 5Restitution and external rotation to realign the head with the fetal torso
Answer
The correct chronological sequence is: Engagement, Flexion, Internal rotation, Extension, and Restitution/External rotation.
The cardinal movements of labor are sequential positional adaptations that allow the fetal head to pass through the anatomically irregular maternal pelvis. The sequence must begin with engagement into the inlet, followed closely by flexion as soft tissue and bony resistance is met. The head must then undergo internal rotation to accommodate the shape of the midpelvis. Once completely rotated, the head delivers via extension under the pubic symphysis. Finally, the newly delivered head undergoes restitution (external rotation) to return to its natural 90-degree alignment with the fetal shoulders, which must subsequently deliver.
Step-by-Step Solution
Key Concept
Cardinal movements of normal labor