The risk of Uterine Rupture and Complications of VBAC associated with a Short interdelivery interval
There is a limited amount of evidence to suggest that becoming pregnant shortly after having a C/S increases the risk of uterine rupture in the subsequent pregnancy. There are generally three intervals of time with decreasing risk of uterine rupture associated with each group.

An interval of pregnancy of less than 6 months since the previous C/S delivery appears to be associated with the highest risk of uterine rupture.

An interval of between 6 months to 2 years appears to have the next lowest risk of uterine rupture.

And an interval of greater than 2 years appears to have the lowest risk of uterine rupture.

Stamilio (2007), in a study involving 286 women who got pregnant within 6 month of their C/S had a uterine rupture rate of 3.05% as compared to 0.9% (3x higher). Stamiliio stated,

"We hypothesized that short interpregnancy intervals may lead to altered wound healing and an increased risk of uterine rupture in patients who attempt a vaginal birth after cesarean. Our hypothesis is based on previous observational studies that suggest an association between short birth interval and increased adverse perinatal outcomes and wound-healing research that indicates that uterine smooth muscle tissue repair evolves over several months... Importantly, there is radiographic and hysteroscopic evidence that cesarean scar development is incomplete as long as 6 or 12 months postoperatively."

Bujold E, Gauthier RJ (2010), in a studiy of 1768 women, found a uterine rupture rate of 1.3% for interdelivery period of 24 months or longer, 1.9% for interdelivery periods between 18-23 months and 4.8% for interdelivery period of less than 18 months.

Based on this limited data, it is recommended that a patient wait 2 years between a previous C/S and the next pregnancy in order to keep the risk of uterine rupture below 1%. If a patient were to become pregnant less than 6 months, with her last delivery being by C/S, she should be counseled that her risks of uterine rupture are between 1-5% and a ERCS over VBAC should be considered. However, there are no specific contraindications to attempting a VBAC.

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