According to ACOG/RCOG guidelines, what is the maximum number of prior vaginal deliveries after which vaginal birth after cesarean (VBAC) is considered contraindicated due to increased uterine rupture risk?

Explanation

## VBAC Candidacy and Uterine Rupture Risk **Key Point:** Prior vaginal deliveries do NOT increase the risk of uterine rupture in VBAC candidates and do not contraindicate trial of labor after cesarean (TOLAC). ### Risk Factors for Uterine Rupture in VBAC | Risk Factor | Impact on VBAC | Evidence | |-------------|----------------|----------| | **Maternal age > 40 years** | Relative contraindication | Increased rupture risk | | **Recurrent indication** (e.g., CPD, FTP) | Relative contraindication | Original reason for CS may persist | | **Vaginal delivery after prior CS** | **PROTECTIVE** | Reduces rupture risk | | **Multiple prior CSs** | Relative contraindication | Cumulative uterine scar risk | | **Maternal obesity** | Relative contraindication | Increases operative risk | | **Maternal race/ethnicity** | No contraindication | Not a valid exclusion criterion | ### Why Prior Vaginal Deliveries Are NOT Contraindications **High-Yield:** Prior vaginal deliveries after a cesarean section actually **reduce** the risk of uterine rupture. This is because: 1. Successful vaginal delivery demonstrates pelvic adequacy 2. The uterine scar has already proven its integrity through labor 3. Each successful VBAC strengthens confidence in future trials of labor ### VBAC Candidacy Criteria (ACOG 2019) **Candidates for TOLAC:** - One or two prior low-transverse cesarean incisions - Adequate pelvis (no history of cephalopelvic disproportion) - No contraindications to vaginal delivery - Maternal motivation and informed consent - **Prior vaginal delivery (increases success rate to ~75%)** **Relative Contraindications:** - Recurrent indication for original cesarean (e.g., failure to progress, cephalopelvic disproportion) - Maternal age > 40 years (modest increase in rupture risk) - Maternal obesity (BMI > 40) - Vaginal delivery not attempted after prior cesarean **Absolute Contraindications:** - Classical (vertical) uterine incision - Unknown uterine incision type - Uterine rupture history - Placenta previa or accreta - Active genital herpes **Clinical Pearl:** A woman with a prior cesarean who has delivered vaginally once is an **excellent** VBAC candidate. Her success rate is higher than a nulliparous woman, and her rupture risk is actually lower than in first-time TOLAC. **Mnemonic — VBAC Contraindications (Absolute):** **CHUMP** - **C**lassical incision - **H**erpes (active genital) - **U**nknown incision type - **M**ultiple prior CSs (relative, but increasing risk) - **P**lacenta previa/accreta