Main Findings
In this study, a clinical multivariate risk model of failed mid-cavity
VAD was developed and validated. The multivariate analysis identified
seven statistically significant and independent risk factors for failed
mid-cavity VAD: a head-perineum distance greater than or equal to 51 mm;
the presence of a bulky caput succedaneum, a maternal height less than
or equal to 1.54 m; a duration of expulsive efforts of less than 21
minutes or greater than 30 minutes before beginning the VAD; a duration
of greater than or equal to three hours from a cervical dilation of five
centimetres to complete cervical dilation; a term of delivery greater
than or equal to 42 weeks of gestation; and an occiput-posterior or
occiput-transverse fetal head position. The statistical method used in
this study calculated the independent OR associated with each of these
variables and allowed a combination of these elements in a quantitative
manner to establish a reliable (Hosmer-Lemeshow test = 8.5; p = 0.39)
and accurate (concordance index = 0.74) score. With the use of a simple
seven-variables scoring system, the risk of failed mid-cavity VAD can be
evaluated quickly to guide the obstetrician in choosing the most
appropriate room for delivery. The threshold to predict a failed
mid-cavity VAD was set at 0.163. Below this value, the VAD attempt could
be conducted in a classical delivery room. Conversely, for a score value
greater than 0.163, an attempt in an operating theatre with anticipated
extension of epidural analgesia and advanced preparation of C-section
equipment should be considered.
The most important risk factor for failed VAD was a head-perineum
distance greater than or equal to 61 mm, corresponding to high-cavity
VAD. High-cavity VADs are difficult and rarely attempted, but their
success rate was close to 50 % in our study. The implementation of the
abovementioned precautions could make it possible to attempt this type
of OVD in the operating theatre with experienced operators and reduce
the number of C-sections.
The results concerning the secondary objective confirmed the interest of
this score. In the case of failed mid-cavity VAD, advanced preparation
of equipment for C-section and anticipated extension of epidural
analgesia were significantly associated with a decrease in the time
interval between mid-cavity VAD and birth. The transfer to an operating
theatre and the anticipated extension of epidural analgesia were
associated with a significant decrease in the rate of general
anaesthesia for the mother. No
improvement of the other maternal or neonatal outcomes appeared with
these precautions in our study. The low number of women included for
this secondary objective (194) may explain this result. When the women
were transferred to an operating theatre for an ultimately successful
VAD, the neonatal outcomes were globally poorer than those of successful
VADs conducted in a standard delivery room. Two factors could explain
these results: the transfer to the operating theatre was probably
decided in the most critical cases, and the delay associated with the
transfer to the operating theatre may worsen neonatal outcomes. These
results confirmed the utility of our predictive score: to better assess
the risk of failed mid-cavity VADs to ensure that only women with a
major risk of failed VAD are transferred to an operating theatre.