Evidence Matters

Does a Low Uterine Incision During Cesarean Lead to Increased Risk of Large Scar Defects?

BACKGROUND AND PURPOSE:

Low uterine incisions may cause increased risk of subsequent large scar defects with potential for dehiscence and/or rupture
Vikhareva et al. (Ultrasound in Obstetrics and Gynecology, 2018) investigated risk of incision level and large uterine scar defects 6-9 months after delivery

Two-center, randomized, single-blind trial (RCT)
- Assessment of the primary outcome was masked
Participants
- Primary section
- Emergent
- Cervical dilation ≥ 5 cm
Large scar defect: Defined as remaining myometrial thickness ≤2.5 mm
Interventions
- High incision: 2 cm above the plica vesicouterina
- Low incision: 2 cm below the plica vesicouterina
Assessment of incisional scar
- Saline contrast sonohysterography at 6-9 months post-surgery
Primary outcome
- Presence of a large scar defect
Secondary outcomes
- Perinatal outcome
- Operative complications within 8 weeks of delivery
- Long-term outcome in subsequent pregnancy

55 women high incision group | 59 women in low incision group
- Median follow-up time 4 years 7 months
- 49% of women had a subsequent pregnancy (56 women)
- Double layer closure used in all participants
Primary Outcome: Incision defects were greater in the low incision group (P < 0.001)
- High incision group: 7% (4 women)
- Low incision group: 41% (24 women)
- Odds ratio (OR): 8.7 (95% CI, 2.8–27.4)
Secondary outcomes: No differences in secondary outcomes

Low cesarean hysterotomy level is associated with a higher risk of scar defects 6-9 months after delivery by a 6-fold higher rate
Authors note that enrollment was stopped early due to changes at the participating hospitals that made compliance with protocol difficult
- However, despite power calculation based on 176 rather than 122 women, the findings were still statistically significant

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