Intra uterine pressure monitoring for induction 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 10.000 deliveries are induced 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 induction of
labour.
PATIENTS: Women in whom labour is induced. Women with a previous 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
Induction of labour can be performed for maternal as well as neonatal reasons. In The Netherlands, it
is applied approximately 10.000 times per year. During induction, 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 induction of
labour 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 induction 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). We are not aware of any studies that report on the effectiveness of IUPC during
induction. 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 induced.
Approach
The proposed research concerns a multicenter randomised clinical trial regarding patients with arrest
of labour in whom labour is induced. The trial will be performed in the Maxima Medical Centre and the
Academic Medical Centre in Amsterdam, The Netherlands.
Patients
All women who in whom labour is induced are eligible for the trial. Women wit 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 and parity.
Interventions
Induction of labour will be performed by amniotomy. In case labour is not progressing, 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 (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