12/26/04njm

Q. How does birth interval affect the repeat cesarean vs vaginal
delivery decision?

A. Intervals \< 18-24 months slightly increase risk, but it is something
the patient can control.

The risk of symptomatic uterine rupture is 0.7%. That risk may increase
by 2-3 times if one has \< 18-24 months interval between pregnancies.
Interdelivery interval is only one of several risk factors, though. (see
below) Interdelivery interval is one of the few risk factors the patient
can control.

**Risk factors** --- Numerous risk factors have been cited for uterine
rupture during labor in women with a previous CD. However, these risk
factors are not consistent across studies, which are hampered by small
numbers of patients with uterine rupture.

Purported risk factors include: maternal age greater than 30 years,
induction of labor with prostaglandins, more than one prior CD,
postpartum fever, interdelivery interval less than 18 to 24 months,
dysfunctional labor, and one layer uterine closure. In contrast, a
previous successful vaginal delivery and a thick uterine scar (greater
than 3.5 mm) on ultrasound examination at 37 weeks of gestation appear
to be protective of scar integrity.

Uterine scarring may be due to events other than previous CD; these
include fetal surgery, uterine surgery (myomectomy, repair of congenital
defects, excision of cornual ectopic pregnancy), or uterine perforation.
Rupture of a scarred or unscarred uterus has also been associated with
trauma (eg, traffic accident, domestic violence, gun shot wound),
obstetric maneuvers (eg, internal version and breech extraction,
instrumental delivery, manual removal of the placenta), obstructed or
neglected labor, and induction (especially with use of prostaglandins or
grand multiparity).

**Vaginal birth after cesarean delivery**

<http://www.uptodateonline.com/application/topic.asp?file=labordel/9085&type=A&selectedTitle=1~6>

**References**

Shipp TD; Zelop CM; Repke JT; Cohen A; Lieberman E Interdelivery
interval and risk of symptomatic uterine rupture. Obstet Gynecol 2001
Feb;97(2):175-7.\
\
OBJECTIVE: To relate interdelivery interval to risk of uterine rupture
during a trial of labor after prior cesarean delivery. METHODS: We
reviewed the medical records of all women who had a trial of labor after
cesarean delivery over 12 years (July 1984 to June 1996). Analysis was
limited to women with only one prior cesarean delivery and no prior
vaginal deliveries who delivered term singletons and whose medical
records included the month and year of the prior delivery. The time in
months between the prior cesarean delivery and the index trial of labor
was calculated, and the women were divided accordingly to permit
comparison with respect to symptomatic uterine rupture. RESULTS: Two
thousand four hundred nine women had trials of labor after one prior
cesarean delivery and had complete data from the medical records. There
were 29 uterine ruptures (1.2%) in the population. For interdelivery
intervals up to 18 months, the uterine rupture rate was 2.25% (seven of
311) compared with 1.05% (22 of 2098) with intervals of 19 months or
longer (P =.07). Multiple logistic regression was used to assess the
risk of uterine rupture according to interdelivery interval while
controlling for maternal age, public assistance, length of labor,
gestational age at least 41 weeks, and oxytocin use. Women with
interdelivery intervals of up to 18 months were three times as likely
(95% confidence interval, 1.2, 7.2) to have symptomatic uterine rupture.
CONCLUSION: Interdelivery intervals of up to 18 months were associated
with increased risk of symptomatic uterine rupture during a trial of
labor after cesarean delivery compared with that for longer
interdelivery intervals.

Esposito MA; Menihan CA; Malee MP Association of interpregnancy interval
with uterine scar failure in labor: a case-control study. Am J Obstet
Gynecol 2000 Nov;183(5):1180-3.\
\
OBJECTIVE: The aim of this study was to determine whether a short
interpregnancy interval is associated with uterine scar failure in
laboring patients with previous low transverse cesarean delivery. STUDY
DESIGN: This was a case-control study of uterine scar failures among
laboring patients with previous low transverse cesarean delivery.
Control patients underwent abdominal delivery during labor after failure
of an attempted vaginal birth after cesarean delivery in the same month
as case patients. RESULTS: An interpregnancy interval of \<6 months was
significantly more prevalent among case patients with uterine scar
failure (P =.02). Mean interpregnancy interval was less in all cases of
uterine scar failure (P = .06). CONCLUSIONS: Interpregnancy interval was
inversely associated with likelihood of uterine scar failure during
subsequent labor.\
\
Bujold E; Gauthier SH Interdelivery interval and uterine rupture. Am J
Obstet Gynecol 2002 Nov;187(5):1199-202.\
\
OBJECTIVE: The purpose of this study was to measure the impact of the
interdelivery interval on uterine rupture during subsequent
delivery.Study Design: An observational cohort study was performed to
assess the rate of uterine rupture in women with a previous low
transverse cesarean delivery and no previous vaginal delivery who
undergo a trial of labor from 1988 to 2000 in a tertiary care center.
The rate of uterine rupture was measured for each of the following
interdelivery intervals: \</=12 months of gestation, 13 to 24 months of
gestation, 25 to 36 months of gestation, and \>36 months of gestation.
Multivariate logistic regression analysis was used to adjust for
selected confounding variables. RESULTS: Of the 1527 women who met the
study criteria, the rate of uterine rupture was 4.8% for patients with
an interdelivery interval of \</=12 months of gestation, 2.7 % for
patients with an interval between 13 and 24 months of gestation, 0.9%
for patients with an interval between 25 and 36 months of gestation, and
0.9% for patients with an interval of \>36 months of gestation (P =.04).
After adjustment for the confounding variables, the odds ratio for
uterine rupture in women with an interdelivery interval of \</=24 months
of gestation was 2.65 (95% CI, 1.08-6.46) and 4.33 (95% CI, 1.70-10.98)
in women with a single-layer closure of the previous uterine incision.
The combination of an interdelivery interval of \</=24 months of
gestation and a single-layer closure of the previous uterine incision
were associated with a rate of uterine rupture of 5.6%. CONCLUSION: An
interdelivery interval of \</=24 months of gestation was associated with
a 2- to 3-fold increase in the risk of uterine rupture compared with an
interval of \>24 months of gestation.\
\
Bujold E; Gauthier SH Interdelivery interval and uterine rupture. Am J
Obstet Gynecol 2002 Nov;187(5):1199-202.\
\
OBJECTIVE: The purpose of this study was to measure the impact of the
interdelivery interval on uterine rupture during subsequent
delivery.Study Design: An observational cohort study was performed to
assess the rate of uterine rupture in women with a previous low
transverse cesarean delivery and no previous vaginal delivery who
undergo a trial of labor from 1988 to 2000 in a tertiary care center.
The rate of uterine rupture was measured for each of the following
interdelivery intervals: \</=12 months of gestation, 13 to 24 months of
gestation, 25 to 36 months of gestation, and \>36 months of gestation.
Multivariate logistic regression analysis was used to adjust for
selected confounding variables. RESULTS: Of the 1527 women who met the
study criteria, the rate of uterine rupture was 4.8% for patients with
an interdelivery interval of \</=12 months of gestation, 2.7 % for
patients with an interval between 13 and 24 months of gestation, 0.9%
for patients with an interval between 25 and 36 months of gestation, and
0.9% for patients with an interval of \>36 months of gestation (P =.04).
After adjustment for the confounding variables, the odds ratio for
uterine rupture in women with an interdelivery interval of \</=24 months
of gestation was 2.65 (95% CI, 1.08-6.46) and 4.33 (95% CI, 1.70-10.98)
in women with a single-layer closure of the previous uterine incision.
The combination of an interdelivery interval of \</=24 months of
gestation and a single-layer closure of the previous uterine incision
were associated with a rate of uterine rupture of 5.6%. CONCLUSION: An
interdelivery interval of \</=24 months of gestation was associated with
a 2- to 3-fold increase in the risk of uterine rupture compared with an
interval of \>24 months of gestation.

Shipp TD; Zelop CM; Repke JT; Cohen A; Lieberman E Interdelivery
interval and risk of symptomatic uterine rupture. Obstet Gynecol 2001
Feb;97(2):175-7.\
\
OBJECTIVE: To relate interdelivery interval to risk of uterine rupture
during a trial of labor after prior cesarean delivery. METHODS: We
reviewed the medical records of all women who had a trial of labor after
cesarean delivery over 12 years (July 1984 to June 1996). Analysis was
limited to women with only one prior cesarean delivery and no prior
vaginal deliveries who delivered term singletons and whose medical
records included the month and year of the prior delivery. The time in
months between the prior cesarean delivery and the index trial of labor
was calculated, and the women were divided accordingly to permit
comparison with respect to symptomatic uterine rupture. RESULTS: Two
thousand four hundred nine women had trials of labor after one prior
cesarean delivery and had complete data from the medical records. There
were 29 uterine ruptures (1.2%) in the population. For interdelivery
intervals up to 18 months, the uterine rupture rate was 2.25% (seven of
311) compared with 1.05% (22 of 2098) with intervals of 19 months or
longer (P =.07). Multiple logistic regression was used to assess the
risk of uterine rupture according to interdelivery interval while
controlling for maternal age, public assistance, length of labor,
gestational age at least 41 weeks, and oxytocin use. Women with
interdelivery intervals of up to 18 months were three times as likely
(95% confidence interval, 1.2, 7.2) to have symptomatic uterine rupture.
CONCLUSION: Interdelivery intervals of up to 18 months were associated
with increased risk of symptomatic uterine rupture during a trial of
labor after cesarean delivery compared with that for longer
interdelivery intervals.