Induction of labor is considered when the benefit of the procedure
is surpasses the benefit of continuation of pregnancy. The rate of induction of singleton pregnancies in US in 2012
was 23.3%, almost more than double a decade ago.
A primed and favorable
cervix is a prerequisite for successful induction of labour.
Numerous methods are in use for cervical ripening to induce
labour, that includes Foley’s catheter( Mechanical Method) to pharmacological
methods including the use of prostaglandins, oxytocin, and mifepristone. Prostaglandin E2, also known as
dinoprostone, is the only prostaglandin that has been approved by the US Food
and Drug Administration (FDA) for cervical ripening in labour induction.
Misoprostol, a prostaglandin E1 analogue is often
used as an off-label drug for inducing labour. Its use is fraught with many
complications from uterine hyper stimulation, rupture and adverse FHR.
Many studies and reviews comparing the safety and efficacy
of different methods have been conducted but the best agent and route is still
unanswered.
The three most common agents widely in use are
dinoprostone, Foley catheter and misoprostol (oral and vaginal). There are many
RCTs comparing these different modalities but no large single trial has compared
them all head to head.
The study conducted by W Chen et al. is a systemic review
and network meta-analysis of all the available RCTs comparing the five most
commonly used methods, published
in the February issue of BJOG: An International Journal of Obstetrics & Gynaecology .
The study aims at providing a comprehensive summary of the
existing evidence to further inform clinical practice and aid in the design of
future trials.
Network meta-analysis, in the
context of a systematic review, is a meta-analysis in which
multiple treatments (that is, three or more) are being compared using both
direct comparisons of interventions within randomized controlled trials and
indirect comparisons across trials based on a common comparator.
The selection criteria was including all the
(RCTs) of cervical ripening during the induction of labour, evaluating
rates of failure to achieve vaginal delivery within 24 hours, incidence of
uterine hyperstimulation with fetal heart rate (FHR) changes, and rates of
caesarean section. Studies including women with prelabour rupture of membranes
were excluded.
Trials were excluded if they included the following cases:
women with pregnancies less than 28
weeks of gestational age; non-cephalic presentations; multiple pregnancies; and
women with previous caesarean sections, combination interventions, non-relevant
outlook and conference papers, posters and abstracts.
A total of 96 RCTs met the selection criteria resulting it a
total of 17387 study subjects.
The interventions included in this review were Foley
catheter, vaginal misoprostol, oral misoprostol, vaginal dinoprostone, and
intracervical dinoprostone.
The primary outcome chosen for network metaanalysis were vaginal
delivery not achieved in 24 hours; uterine hyperstimulation with FHR changes;
and caesarean section.
The meta-analysis compared five different modalities of
cervical ripening for induction of labour. It was seen that:
The rank probabilities of reducing the number of vaginal
delivery not achieved in 24 hours according to different interventions from
best to worst are vaginal misoprostol (100%), vaginal dinoprostone (95%), Foley
catheter (59%), oral misoprostol and intracervical dinoprostone
The rank probabilities of not causing hyper stimulation with FHR
changes from best to worst are Foleys catheter (90%), intracervical
dinoprostone, oral misoprostol, vaginal dinoprostone, and vaginal misoprostol (99%).
The rank probabilities of different intervention in
decreasing the rate of caesarean sections, from best to worst are oral misoprostol
(83%), vaginal misoprostol (80%), vaginal dinoprostone, intracervical dinoprostone
and Foley’s catheter.
Thus it was seen that although vaginal misoprostol was the
most effective intervention for achieving vaginal delivery within 24 hours, but
it came at the cost of highest rate of uterine hyperstimulation with FHR
changes. Vaginal dinoprostone was second best vaginal delivery withi 24 hours.
Foley catheter was found to be the least likely to cause
hyperstimulation, but is worse than both vaginal misoprostol and vaginal
dinoprostone in achieving vaginal delivery within 24 hours.
Compared to Vaginal misoprostol, oral misoprostol had lesser
incidences of uterine hyperstimulation but at the expense of slightly decreased
number of vaginal deliveries in 24 hours, but this difference was not
statistically significant.
In most countries misoprostol is not legalized to be used
for induction of labor, because of the concerns of hyperstimulation. The study
shows that oral misoprostol is safe in comparison to vaginal misoprostol and it
also performed better than vaginal dinoprostone.The other advantage of misoprostol is it is effective,
cheap, does not requires cold storage; the dose can be measured and precise as
compared to vaginal route. It is the first drug of choice in developing
countries.
Foley catheter has similar effect as oral misoprostol in
achieving vaginal delivery. It is
inferior to prostaglandins in decreasing the C section rates but superior to
use of Oxytocin alone. It may be highly indicated in women with high risk of
Fetal hypoxaemia like postdate pregnancies, sickle-cell disease, pre-eclampsia,
or intrauterine growth restriction, due to it’s least effect on
hyperstimulation . It also has advantages in terms of cost and storage
conditions, less stringent monitoring of uterine contraction and no medical
intervention until it is expelled in labor.The drawback is high rate of chorioamnionitis, but
metaanalysis was not performed due to lack of reporting of this data in most
trials.
Conclusion:
Vaginal misoprostol followed by vaginal dinoprostone are
most effective methods for induction of labor beyond 28 weeks of gestation with
intact membranes, in terms of achieving vaginal delivery. However they are also
associated with uterine hyper
stimulation and adverse FHR requiring close monitoring.
Mechanical stimulation by Foley catheter was least effective
method for vaginal delivery, along with oral misoprostol and intracervical
dinoprostone, but caused the least uterine hyper stimulation and adverse FHR.
Oral misoprostol was the best method in terms of overall
safety, least likelihood of uterine hyperstimulation and adverse FHR and
reducing the likelihood of cesarean section than vaginal misoprostol.
References:
A systematic
review and network meta-analysis comparing the use of Foley catheters,
misoprostol, and dinoprostone for cervical ripening in the induction of labour.
BJOG 2016;123:346–354.
, , ,
, , , .
Hemming, K. and Price, M. (2016), Is it oral or vaginal; and
should it be misoprostol or dinoprostone for cervical ripening? How to
interpret a network meta-analysis. BJOG: An International Journal of Obstetrics
& Gynaecology, 123: 355. doi: 10.1111/1471-0528.13533
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