# Situation: A 28-year-old woman at 40 weeks' gestation, who had one previous term vaginal birth, is in the second stage of labor at a lying-in clinic that follows the Department of Health (DOH) Essential Intrapartum and Newborn Care (EINC) protocol. Her first stage was uncomplicated, and the fetus is in a vertex presentation. The nurse explains the mechanism of labor to a nursing student. After engagement and descent, in what order do these cardinal movements occur? 1. Extension 2. Internal rotation 3. External rotation 4. Flexion

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=629378  
> language: ko  
> subject: Nursing Practice II — Maternal and Child Health Nursing

## 문제

Situation: A 28-year-old woman at 40 weeks' gestation, who had one previous term vaginal birth, is in the second stage of labor at a lying-in clinic that follows the Department of Health (DOH) Essential Intrapartum and Newborn Care (EINC) protocol. Her first stage was uncomplicated, and the fetus is in a vertex presentation.

The nurse explains the mechanism of labor to a nursing student. After engagement and descent, in what order do these cardinal movements occur?
1. Extension
2. Internal rotation
3. External rotation
4. Flexion

## 보기

1. 4, 1, 2, 3
2. 2, 4, 1, 3
3. 4, 2, 1, 3 **✔ 정답**
4. 4, 2, 3, 1

**정답: 3**

## 해설

In a vertex presentation the head flexes so its smallest diameter leads, then rotates internally so the occiput turns anterior. The head is born by extension under the symphysis pubis, and then restitution and external rotation realign it with the shoulders before expulsion.

## 심화 해설

The correct sequence of cardinal movements
In a vertex presentation, the fetal head does not simply slide straight down the birth canal. It must adapt its position to the changing shape of the maternal pelvis, and these adaptations are called the cardinal movements of labor. After engagement and descent, the order is flexion, then internal rotation, then extension, and finally external rotation, which is the sequence 4, 2, 1, 3. Restitution occurs just before external rotation, and expulsion of the shoulders and body completes the mechanism. Each movement prepares the head for the next one, so the order follows the anatomy of the pelvis, not chance.

Why flexion comes first
As the head descends and meets resistance from the cervix, the pelvic floor, and the walls of the pelvis, the chin is pressed toward the chest. This flexion changes the leading diameter from the larger occipitofrontal diameter to the smaller suboccipitobregmatic diameter, so the smallest part of the head leads the way. Without good flexion, a larger diameter must pass through the pelvis, and labor tends to be slower. Flexion must therefore happen before the head reaches the level where it needs to rotate.

Internal rotation and extension
The pelvic inlet is widest in its transverse diameter, while the outlet is widest in its anteroposterior diameter. The well-flexed head therefore rotates internally, usually so that the occiput turns anterior toward the symphysis pubis. Only after this rotation can the occiput slip under the pubic arch. The head is then born by extension: the base of the occiput pivots under the symphysis, and the face, nose, mouth, and chin sweep over the perineum. Key point! Extension cannot happen before internal rotation, because an unrotated occiput would not be positioned to pass under the symphysis.

Restitution and external rotation
Once the head is born, it is free of the pelvis and turns back to realign with the shoulders, which are still inside. This untwisting is restitution. The head then turns further as the shoulders rotate internally to lie in the anteroposterior diameter of the outlet, which is seen outside as external rotation. The anterior shoulder is then delivered under the symphysis, followed by the posterior shoulder and the rest of the body. External rotation always follows birth of the head, so it can never come before extension.

How the distractors go wrong
The option 4, 1, 2, 3 places extension before internal rotation, which skips the step that brings the occiput under the symphysis. The option 2, 4, 1, 3 places internal rotation before flexion, even though the smallest diameter must lead before rotation occurs. The option 4, 2, 3, 1 places external rotation before extension, which is impossible because external rotation is a movement of the head after it has already been born. Watch out! Exam items often list the movements out of order; anchor on the idea that rotation inside the pelvis comes before birth of the head, and rotation outside the body comes after it.

Exam takeaway
Memorize the full sequence: engagement, descent, flexion, internal rotation, extension, restitution, external rotation, and expulsion. Flexion makes the head small, internal rotation lines it up with the outlet, extension delivers it, and external rotation realigns it with the shoulders. When the nurse explains this to a student, linking each step to pelvic shape makes the order logical rather than something to memorize blindly.

## 임상 시나리오

Cardinal Movements of LaborVertex presentation, after engagement and descent
Order after engagement and descent: flexion, internal rotation, extension, restitution, external rotation, then expulsion of the shoulders and body.

Flexion brings the smallest diameter of the head forward. Internal rotation turns the occiput anterior so it can pass under the symphysis pubis, and the head is born by extension.

After birth of the head, restitution and external rotation realign the head with the shoulders before the anterior and posterior shoulders are delivered.

CautionExternal rotation happens outside the body after the head is born. Any sequence that places it before extension, or extension before internal rotation, is wrong.

## 핵심 개념

- **Cardinal movements** — The positional changes of the fetal head and body as they pass through the maternal pelvis during labor.
- **Flexion** — Bending of the fetal chin toward the chest so the smallest head diameter leads through the pelvis.
- **Internal rotation** — Turning of the fetal head inside the pelvis so the occiput moves anterior toward the symphysis pubis.
- **Extension** — Movement by which the head is born as the occiput pivots under the symphysis and the face passes over the perineum.
- **External rotation** — Turning of the born head to realign with the shoulders as they rotate inside the pelvis.

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