A 28-year-old primigravida at term presents in active labor. After 2 hours of pushing in the second stage, the fetal head is at +2 station in the occipitoanterior position. Maternal vital signs are stable, and fetal heart rate is 140 bpm with reassuring variability. The obstetrician decides to apply forceps. Which of the following is the MOST important prerequisite that must be confirmed before proceeding with instrumental delivery?

Explanation

## Prerequisites for Instrumental Delivery **Key Point:** Before any forceps or vacuum application, the cervix MUST be fully dilated (10 cm) and completely retracted. Attempting instrumental delivery with an incompletely dilated cervix is a contraindication and risks severe maternal trauma (cervical lacerations, uterine rupture) and fetal injury. ### Essential Preconditions Checklist | Prerequisite | Rationale | |---|---| | **Full cervical dilation (10 cm)** | Incomplete dilation → cervical trauma, hemorrhage, uterine rupture | | **Complete cervical retraction** | Ensures cervix is not trapped between fetal head and maternal pelvis | | **Adequate pelvis** | Clinical pelvimetry or imaging to exclude cephalopelvic disproportion | | **Engaged head** | Station ≥ +2 (preferably +3 or below) for outlet/low forceps | | **Ruptured membranes** | Allows access to fetal head; intact membranes = contraindication | | **Maternal anesthesia/analgesia** | Adequate pain relief (epidural, spinal, or pudendal block) | | **Empty bladder** | Reduces injury risk; catheterization if needed | **Clinical Pearl:** In this case, the patient has been pushing for 2 hours, the head is at +2 station (engaged), and fetal well-being is reassuring. The question tests whether you recognize that cervical status is the **gating criterion** — without full dilation and retraction, no instrument should be applied, regardless of other favorable factors. **High-Yield:** The "rule of 3 Cs" for safe instrumental delivery: 1. **Cervix** — fully dilated and retracted 2. **Cephalic presentation** — confirmed (not breech, face, or brow) 3. **Capacity** — adequate pelvis (no CPD) **Tip:** Episiotomy is NOT a prerequisite — it is performed selectively (mediolateral preferred to prevent 3rd/4th-degree tears) and should not be routine. Fetal scalp pH is a tool for fetal assessment in the context of non-reassuring FHR, not a prerequisite for instrumental delivery when FHR is already reassuring.