Assessment of the rate of uterine rupture at the first prenatal visit: A preliminary evaluation

We read, with great interest, the paper by Shipp et al., who reported that a simple scoring system could better estimate the patient-specific risk of uterine rupture after prior cesarean section [1]. Most of the risk factors evaluated in their score were extracted from studies of their patient population. Since external validation of this score has not yet been demonstrated, we tested it in our own patient population.

Analyzing all available data on 2493 women who underwent a trial of labor after prior cesarean section at Sainte-Justine Hospital, Montreal, between 1993 and 2004, we calculated the score for each patient and the corresponding rate of uterine rupture according to the study of Shipp et al. Although we found a similar trend in uterine rupture rates, the scoring system did not discriminate well those women at low risk for uterine rupture (Table I). As suggested by the authors, additional factors, such as type of closure, could improve the score [2]. As a demonstration, we repeated the calculation after adding 1 point for women with single-layer closure and removing the variable ‘age between 30 and 39 years' [3]. In our series, this modified scoring system better discriminated low- versus high-risk populations with almost 70% of the population having a <0.8% risk of uterine rupture (Table I).

Table I.  Rate of uterine rupture according to the original score or modified score and the presence or absence of labor induction.

Score	% (n) with score	% (n) with rupture/no labor induction	% (n) with rupture and labor induction	% (n) with rupture, total
Original scoring system*
−1	7.1% (177)	0% (0)	0% (0)	0% (0)
0	41.2% (1026)	1.1% (8)	0.7% (2)	1.0% (10)
1	44.0% (1096)	1.3% (11)	2.9% (8)	1.7% (19)
≥2	7.8% (194)	0% (0)	0% (0)	0% (0)
Modified scoring system^†
−1	21.3% (532)	0.3% (1)	0% (0)	0.2% (1)
0	48.3% (1203)	0.6% (5)	0.9% (3)	0.7% (8)
1	22.9% (570)	2.4% (10)	3.2% (5)	2.6% (15)
≥2	7.5% (188)	2.2% (3)	4.0% (2)	2.7% (5)

*Original scoring system (Shipp et al. [1]): interdelivery interval <18 months = 1 point, maternal age 30–39 years = 1 point, maternal age >40 years = 2 points, ≥2 cesareans = 2 points, prior vaginal delivery = −1 point. ^†Modified scoring system: interdelivery interval <18 months = 1 point, maternal age >40 years = 2 points, ≥2 cesareans = 2 points, prior vaginal delivery = −1 point, single-layer closure = 1 point.

In addition, we believe that it is important to mention the utility of measuring lower uterine segment thickness near term by ultrasound as a predictive factor, since it has been associated with a very high likelihood ratio for uterine rupture [4]. Until now, no study has evaluated the independent effect of this measurement on the risk of uterine rupture after adjustment for confounding factors, such as interdelivery interval, maternal age, and type of uterine closure [5]. We believe that there is a need to do so, to appropriately counsel women contemplating a trial of labor after prior cesarean section.