Cephalopelvic Disproportion (CPD)
CPD occurs when there is a mismatch between the size of the fetal head and the size of the maternal pelvic brim or cavity, preventing a successful vaginal delivery. It is a clinical diagnosis usually made during the course of labor.
Key Contributing Factors
- Fetal Factors: Macrosomia, hydrocephalus, or malposition (e.g., asynclitism).
- Pelvic Factors: Contracted pelvis (e.g., platypelloid or android pelvic shapes), previous pelvic fractures, or rickets.
- Uterine Factors: Inefficient uterine contractions (dystocia) often mimic true CPD.
Clinical Indicators
| Clinical Finding | Interpretation |
|---|---|
| Labor Arrest | Lack of cervical dilation or fetal descent despite adequate uterine contractions (as assessed by IUPC). |
| Molding/Caput | Excessive fetal skull molding or caput succedaneum formation can suggest mechanical obstruction. |
High-Yield Exam Pearl:
- Diagnosis: CPD cannot be accurately diagnosed until the patient has undergone an adequate trial of labor with appropriate uterine activity.
- Clinical Trap: Do not rush to a diagnosis of CPD during the latent phase of labor. Always rule out secondary arrest of labor due to inadequate uterine activity or malposition before committing to a cesarean section for “CPD.”