Induction of labor is one of the most common practices in
obstetrics. More than 20% of pregnant women are delivered after
the induction of labor, and the overall rate of induction of labor in
the United States has become more than doubled from 1990 to
2006 [1]. The induction of labor is usually performed as
a therapeutic option when the benefits of expeditious delivery
outweigh the risk of continuing pregnancy. However the patient
should be counseled about the increased risk of cesarean delivery,
especially in nulliparous women[2–10].
For this reason, previous investigators have tried to identify risk
factors for cesarean deliveries during the induction of labor.
Nulliparity, advanced gestational age, increased birthweight, and
use of cervical ripening agent have been reported as risk factors for
cesarean delivery [8,11]. And, on the basis of these risk factors,
several investigators offered scoring system for risk of cesarean
section during the induction of labor [12–16].
However, there is little information on the timing of ROM
during induced labor at term as a risk factor for cesarean delivery.
We have recently demonstrated that spontaneous early rupture of
membranes (early ROM) is an independent risk factor for cesarean
delivery in nulliparous women who delivered after the spontaneous
onset of labor [17]. It has been theorized that spontaneous
early ROM is more likely in women with cephalopelvic
disproportion, because the entire force of labor converges on the
portion of the membranes that overlies the cervix in contracted
pelvis that precludes the passage of the fetus [17,18].
It is an important issue if there is a relationship between the
occurrence of early ROM and the risk of cesarean delivery in
induced labor, because prediction of the risk for cesarean delivery
is not straightforward in clinical management of induced labor,
which itself increases the risk of cesarean delivery[2,5–10], and the
timing of ROM is the kind of information that is readily available
to physicians in the clinical setting. In addition, induced labor may
be a better model for demonstration of a relationship between
early ROM and risk of cesarean delivery than spontaneous onset
of labor, because both the initiation of labor and ROM always
occurs in the hospital during labor induction, resulting in a clear
distinction between early ROM and late ROM.
To address this issue, we undertook this study to determine if
spontaneous early ROM during induction of labor is associated
with an increased risk for cesarean section in term nulliparas.