Persalinan Lama

01Pathophysiology

Normal labor depends on the coordinated interaction of three fundamental variables known as the 3 P's: Power, Passenger, and Passage. Abnormal labor occurs when any one of these components is deficient, and the exam will frequently test your ability to identify which P is the culprit based on the clinical scenario.

Power refers to the strength and coordination of uterine contractions. Normal active labor requires contractions that generate sufficient intrauterine pressure to dilate the cervix. This is quantified using Montevideo units (MVU), calculated by summing the peak amplitude above baseline (in mmHg) of each contraction over a 10-minute window. A value of 200 MVU or greater is considered adequate. When contractions are hypotonic (too weak) or incoordinate (unorganized), the cervix dilates slowly or not at all. This is the most common and most correctable cause of labor abnormalities, which is why oxytocin augmentation is the first intervention tested on exams.

Passenger refers to the fetus, including its size, lie, presentation, and position. Macrosomia (estimated fetal weight > 4,000 g, or > 4,500 g in diabetic mothers) increases the risk of labor arrest because the fetal head or shoulders cannot navigate the pelvic inlet and midpelvis. Occiput posterior (OP) position is a high-yield exam concept: the fetal head presents with a larger diameter, leading to protracted descent even with adequate contractions. Malpresentations such as brow or face presentation similarly increase the presenting diameter and cause dystocia.

Passage refers to the bony pelvis and soft tissues. A contracted pelvis (e.g., android or platypelloid pelvic types) narrows the available space for fetal descent. Soft tissue causes include cervical scarring, large fibroids in the lower uterine segment, or a distended bladder. If the passage is the limiting factor, augmentation with oxytocin will not resolve the problem, and continued augmentation against an obstructed pelvis risks uterine rupture. This is the key reason the exam tests whether you can differentiate "power" problems (treatable with oxytocin) from "passage" or "passenger" problems (requiring cesarean delivery).

The partograph is the clinical tool that connects pathophysiology to diagnosis. By plotting cervical dilation and fetal descent against time, you can objectively identify when labor has deviated from normal. Modern labor management has shifted from the classic Friedman curve to evidence from the Zhang/ACOG Safe Prevention of the Primary Cesarean guidelines, which recognize that labor before 6 cm can be physiologically slower than previously thought.

02Classification and Clinical Manifestation

Phases of Labor

Abnormal Labor Patterns

Protraction vs. Arrest

03Diagnostic Workup

The best initial step in evaluating suspected abnormal labor is a cervical examination to establish current dilation, effacement, station, and fetal position. This must be compared to prior exams to determine whether there is protraction (slow progress) or arrest (no progress). The partograph is the standard visual tool for this purpose.

If there is concern that contractions are inadequate, the next step is to quantify contraction strength. External tocometry can tell you frequency and duration but not amplitude. If the clinical picture suggests a power problem (i.e., contractions feel weak, cervix is slowly dilating, and there is no evidence of CPD), placement of an IUPC is the confirmatory test. Montevideo units below 200 indicate inadequate contractions, which gives you a clear rationale to augment with oxytocin before labeling the labor as arrested.

Ultrasound is used to evaluate the passenger. If the cervix has arrested despite adequate contractions, you need to assess fetal weight (to rule out macrosomia), confirm the presentation is vertex, and check for OP position. An estimated fetal weight above 5,000 g in a non-diabetic mother or above 4,500 g in a diabetic mother is an indication for cesarean delivery regardless of labor progress.

An important exam concept: you cannot diagnose active phase arrest until the patient is at least 6 cm dilated. Before 6 cm, slow progress is considered prolonged latent phase, and the management is different (therapeutic rest or augmentation, not cesarean).

04Management and Treatment

Prolonged Latent Phase

The latent phase is the most variable part of labor, and the exam frequently tests that cesarean delivery should not be performed solely for a prolonged latent phase. Management options include therapeutic rest (morphine sulfate 10 to 15 mg IM with promethazine 25 mg to allow the patient to sleep; most will awaken in active labor) or augmentation with oxytocin (starting at 1 to 2 mU/min, increased every 15 to 30 minutes). Amniotomy can also be performed if membranes are intact and the head is well-applied to the cervix.

Active Phase Protraction and Arrest

Once the patient is at least 6 cm, active phase criteria apply. The approach is sequential and exam-testable:

1. Amniotomy if membranes are intact. This alone can increase contraction strength and accelerate dilation.

2. Oxytocin augmentation, starting at 1 to 2 mU/min IV, titrated upward every 15 to 30 minutes. The goal is to achieve at least 3 contractions per 10 minutes with MVU of 200 or greater.

3. IUPC placement to objectively measure contraction adequacy when external monitoring is equivocal.

4. If adequate contractions (MVU > 200) are documented for at least 4 hours with no cervical change, active phase arrest is diagnosed, and cesarean delivery is indicated.

5. If contractions remain inadequate despite oxytocin (MVU remains < 200), you must allow up to 6 hours of augmentation before declaring arrest and proceeding to cesarean.

These time thresholds (4 hours adequate, 6 hours inadequate) come from ACOG guidelines and are heavily tested.

Second Stage Disorders

For protracted or arrested descent, first ensure the patient is actively pushing with adequate technique. Position changes (e.g., squatting, lateral positioning) can help. If the fetal head is at station +2 or below and all criteria for operative vaginal delivery are met (known position, adequate pelvis, vertex presentation, fully dilated cervix, engaged head, ruptured membranes, empty bladder), vacuum extraction or forceps can be attempted. If operative vaginal delivery fails or criteria are not met, cesarean delivery is performed.

Contraindications and Cautions

Oxytocin is contraindicated in the setting of a prior classical (vertical) uterine incision, active placenta previa, vasa previa, cord prolapse, and non-reassuring fetal heart tracing (category III). Augmentation with oxytocin in a patient with a prior low transverse cesarean is permitted for trial of labor after cesarean (TOLAC) but requires continuous fetal monitoring due to the risk of uterine rupture.

Tachysystole (more than 5 contractions in 10 minutes) during oxytocin administration requires immediate reduction or discontinuation of oxytocin, repositioning the patient to the left lateral decubitus position, and administering IV fluid bolus. If fetal heart rate abnormalities accompany tachysystole, terbutaline 0.25 mg subcutaneous can be given as a tocolytic to relax the uterus.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most tested trap in labor abnormalities is performing cesarean delivery too early. The exam will present a woman at 4 or 5 cm who has been laboring for many hours with slow progress and ask you what the next step is. The correct answer is almost never cesarean at this point, because active phase criteria do not apply until 6 cm. Before 6 cm, the management is therapeutic rest or augmentation, not surgical delivery. Students who choose cesarean in this scenario are penalized for not understanding the revised definition of active labor.

The second major trap involves the distinction between adequate and inadequate contractions when diagnosing arrest. If a vignette describes a patient at 7 cm with no cervical change for 3 hours, but does not mention MVU or contraction adequacy, the next best step is not cesarean. The correct answer is to place an IUPC or ensure contractions are adequate before declaring arrest. You must demonstrate adequate power before blaming the passenger or passage.

A third high-yield pearl: the exam loves to test OP position as the sneaky cause of protracted descent. The vignette will describe a patient who is fully dilated, pushing for a long time, with the fetal head "at 0 station" and the fontanelle palpable anteriorly on vaginal exam (meaning the posterior fontanelle is posterior, confirming OP). The correct recognition of OP position may lead to a question about manual rotation or operative vaginal delivery.

Finally, remember that amniotomy is always performed before oxytocin augmentation in most management algorithms. If the vignette gives you a patient with intact membranes and poor progress, amniotomy is the correct first step before escalating to IV oxytocin. Getting the sequence right (amniotomy then oxytocin, not the reverse) is a frequently tested ordering question.

The core competency being tested is your ability to differentiate correctable causes of abnormal labor from those requiring surgical delivery, apply the correct time thresholds before diagnosing arrest, and avoid premature cesarean section while also recognizing when continued augmentation becomes unsafe.