Objective: To estimate the effect of birth weight difference between the current and index pregnancy on vaginal birth after cesarean (VBAC) failure in patients whose prior cesarean was for cephalopelvic disproportion (CPD).
Methods: This was a retrospective cohort study of women with one cesarean for CPD, comparing the rate of VBAC failure in women whose infant was smaller, the same, or larger in the VBAC attempt compared with cesarean. The primary outcome was VBAC attempt failure, defined as a patient who attempted VBAC but subsequently required a cesarean delivery for any indication. Univariable, stratified, and multivariable analyses were used.
Results: Of 13,706 patients attempting VBAC, 1,511 had one prior cesarean delivery for CPD. Compared with patients with the same birth weight, a lower birth weight was associated with fewer failed VBAC attempts (29.6% compared with 37.8%, adjusted odds ratio [OR] 0.7, 95% confidence interval [CI] 0.5-1.0) and a higher birth weight was associated with more failed VBAC attempts (54.5% compared with 37.8%, adjusted OR 2.0, 95% CI 1.5-2.8).
Conclusion: Birth weight difference has a moderate effect on the rate of VBAC success in patients whose prior cesarean delivery was for CPD.
Level of evidence: II.