Intra uterine pressure monitoring for augmentation of labour:
Benefits and costs.
Protocol
Ben W. J. Mol
Gynaecoloog
Maxima Medical Centre
Department Obstetrics/Gynaecology
De Run 4600
5504 DB Veldhoven
tel: +31-40-8889551
fax: +31-(0)40-2588387
Dr. J.A.M. van der Post
Gynaecoloog
Academic Medical Centre
Department Obstetrics/Gynaecology
PO Box 22600
1100 DD Amsterdam
tel: +31-(0)20-5663857 (Wednesday)
fax: +31-(0)20-6963489
PROBLEM: In The Netherlands, approximately 15.000 deliveries are augmented with oxytocin each
year (LVR 2, 2002). Many clinicians monitor frequency and strength of contractions with an
intrauterine pressure catheter (IUPC). It is questionable whether monitoring contractions with IUPC is
beneficial in terms of maternal or fetal outcome and whether it is cost effective.
AIM: To evaluate the effectiveness of IUPC in comparison to external monitoring during (I)
augmentation after arrest of labour).
PATIENTS: Women with arrest of labour in whom labour is augmented. Women with a history of
caesarean section are excluded from the study.
INTERVENTIONS: Women will be at random allocated to placement of an IUPC (intervention group)
or external uterine activity monitoring (control group).
OUTCOME: The primary outcome measure will be the number of instrumental deliveries, i.e.
caesarean sections and/or assisted vaginal delivery. Secondary outcome measures are the
occurrence of neonatal admittance to ICU, need for antibiotics by mother or child, total amount of
oxytocin used, complications, time to delivery and costs.
ANALYSIS: The study will be designed as an equivalence study. Under the assumption of equal
neonatal and maternal morbidity, it is hypothesised that IUPC will reduce the number of instrumental
deliveries from 25% to 16%. Analysis will be by intention to treat. We will need 337 women in each
arm (overall 674 women).
Keywords: Intra uterine pressure catheter, oxytocin, assisted deliveries.
Problem
Augmentation of labour is the treatment of choice in women in whom labour arrest is diagnosed. It is
by far the most common reason for referral of women during labour to the hospital. In The
Netherlands, many clinicians monitor frequency and strength of contractions with an intrauterine
pressure catheter (IUPC) in case of augmentation. However, it is questionable whether monitoring
uterine contractions with IUPC during augmentation of labour with oxytocin is needed (Lucidi et al
2001). Although an IUPC measures intra uterine activity more accurately compared to extra uterine
monitoring, the use of an IUPC during augmentation of labour has not been reported to have a
positive effect on maternal or perinatal outcome compared to extra uterine assessment of
contractions. In a study that described 39 patients with a uterine rupture during labour while monitored
with IUPC, the classic description of a loss of intrauterine pressure or cessation of labour was not
observed in any of the patients, thus questioning the prevention of uterine rupture (Rodriguez et al
1989). There is only one randomised clinical trial involving 250 patients with augmentation of labour
that compares obstetric outcome after external tocography and IUPC. This study did not demonstrate
a clear benefit from IUPC, but due to the low numbers the precision of this conclusion was limited
(Chua et al 1990).
The value of an IUPC is further questioned by the potential of infrequent but potentially hazardous
risks associated with insertion like placental or fetal vessel damage and infection. The frequency of
these risks is estimated to be between 1:300-1:1400 (e.g. Chan WH 1973, Trudinger 1978).
Still, IUPC's are widely used in daily practice. The use of oxytocine to augment labor is considered to
demand uterine activity monitoring to prevent serious maternal and fetal complications. Arguments are
prevention of hyper stimulation or uterine rupture, associated with concomitant fetal distress,
shortening of duration of labour and/or reduced use of total amount of oxytocin needed.
Consequently this could e.g. lead to a reduction in caesarean section rate through prevention of fetal
distress. Indeed, differences are reported in contraction amplitude and duration between IUPC and
external monitoring (Miles AM 2001). The guideline of the Dutch Society of Obstetrics and
Gynaecology (NVOG, Richtlijn no 5, Inleiden van de baring, Feb 1997) recommends the use of IUPC
by stating that "Uterine activity can best be quantified by IUPC".
In view of this discrepancy between current practice and the direction of the small amount of available
evidence, we propose a randomised comparison of external contraction monitoring and the use of
IUPCs in women in whom labour is augmented due to shortness of expulsive force.
Approach
The proposed research concerns a multicenter randomised clinical trial regarding patients with arrest
of labour in whom labour is augmented. The trial will be performed in the Maxima Medical Centre and
the Academic Medical Centre in Amsterdam, The Netherlands.
Patients
All women who are spontaneously in labour, and in whom the clinician has decided for augmentation
with oxytocin for arrest of labour, are eligible for the trial. Women with a history of caesarean section
are excluded from the study.
All women will be asked informed consent by the attending physician or midwife.
After patients have consented for participation in the study, patients will be randomised to either
placement of an IUPC (intervention group) or management by extra uterine measurement of
contraction frequency (control group). Patients presenting with intra uterine fetal death and/or breech
presentation will not be included. Randomisation will be done at a central office, and will be stratified
for centre, parity and presence of meconium.
Interventions
Augmentation of uterine contractions will take place with oxytocin given intravenously in fixed
increasing dosages according local protocol until either 4 contractions in 10 minutes are recorded
(control group) or at least 200 Montevideo Units are recorded (intervention group) and adequate
progression of cervical disclosure is reached (both intervention and experimental group). Adequate
progression is defined as shortening and effacement of the cervix if no dilatation is found and at least
an increase of 1 cm/hr of dilatation of the cervix after the cervix is fully effaced. If there is an indication
for amnion infusion during labour either before trial entry or after the randomisation has occurred,
amnion infusion is allowed during the study. In case amnion infusion is indicated in women allocated
to the external monitoring group, the IUPC will be placed without connection to a monitor, in order to
allow amnion infusion. Complications caused by use of an IUPC will be noted. Progression of cervical
dilatation is measured by digital examination with regular intervals equal in both groups and according
to local protocol. Fetal monitoring will consist of direct fetal heart rate monitoring in combination with
fetal blood sampling if deemed necessary. Strict criteria for progression of labour will be handled in
both groups. If no progression in cervical dilatation is found in three hours despite adequate uterine
contraction a caesarean section is to be considered.
Outcome
The main outcome measure will be the number of instrumental deliveries, i.e. caesarean sections
and/or assisted vaginal delivery. Secondary outcome measures will be the occurrence of neonatal
admittance to ICU, need of antibiotics by mother or child, total amount of oxytocin used, complications
(abruptio placentae, fetal vessel damage, uterine rupture, sepsis) and finally, time to delivery, and
costs.
Statistics
Data will be collected in case record forms and entered at a central database. The study will be
designed as an equivalence study. Under the assumption of equal maternal and neonatal morbidity, it
is hypothesised that management with IUPC management will reduce the number of instrumental
deliveries from 25% to 16% in both groups. If we use a two-sided test with a significance level of 5%
and a power of 80%, there are 337 patients required in both groups in each trial (overall 674 patients)
to answer the question. In the participating centres, approximately 4.000 patients deliver each year
with a singleton pregnancy at term in vertex position. If we assume that 15% of these patients needs
either augmentation the required number of patients are within the reach of the present proposal.
The initial analysis will be according to the intention to treat principle. In a second analysis, we will
assess the effectiveness of IUPC in those women in whom the technique could be applied according
to plan.
References
1. Lucidi RS, Chez RA, Creasy RK. The clinical use of intra uterine pressure catheters. J Matern Fetal
Med 2001;10:420-22.
2. Rodriguez MH, Masaki DI, Phelan JP, Diaz FG et al. Uterine rupture: are intrauterine pressure
catheters useful in the diagnosis? Am J Obst Gynecol 1989;161:666-9.
3. Chua S, Kurup A, Arulkumaran S. Augmentation of labor: does internal tocography result in better
obstetric outcome than external tocography? Obstet Gyn 1990;76(2):164-7.
4. Chan WH, Paul RH, Toews J. Intrapartum fetal monitoring: Maternal and fetal morbidity and
perinatal mortality. Obstet Gynecol 1973;41:7-13.
5. Trudinger BJ, Pryse-DaviesJ. Fetal hazards of the intrauterine pressure catheter: five case reports.
Br J Obstet Gyn 1978;85:573-74.
6. Miles AM, Monga M, Richeson KS. Correlation of external and internal monitoring of uterine
activity in a cohort of term patients. Am J Perinatol 2001;18:137-140.
7. NVOG-richtlijn no 5: Inleiden van de baring, February 1997. http://www.nvog.nl