Open Jo urnal of Obst etrics and Gynecology, 2011, 1, 113-120 OJOG
doi:10.4236/ojog.2011.1302 0 Published Online September 2011 (
Published Online September 2011 in SciRes.
Labour analgesia effects on foetal heart rate. A mini-review
Nicole Mari a Anna Adela Engel1*, Marc Van de Velde2, Jan Gerrit Nijhuis3,
Marca Abraham Emmanu e l M arc us1
1Department of Anaesthesiology an d Pain Management, Maastricht University Medical Centre, Maastricht, Netherlands ;
2Department of Anaesthesiology, Katholieke Universiteit Leuven, University Hospitals Gasthuisberg, Leuven, Belgium;
3Department of Obstetr ics and Gynaecology, Maastricht University Medical C entre, Maastricht, Netherlands.
E-mai l : *
Hnico l e.engel@mumc.nlH
Received 24 June 2011; revised 1 September 2011; accepted 8 September 2011.
Foetal well-being during labour is of utmost impor-
tance. One of the ways to attempt to assess foetal well-
being is by recording foetal heart rate (F HR). Loss of
variability and deceleration patterns are known to be
associated with foetal distress. Decelerations and foe-
tal bradycardia have been described after any type of
effective labour analgesia. This review addresses the
questions if certain analgesic techniques and/or anal-
gesics lead to clinically relevant FHR changes, what is
their aetiology, and how we should manage these
FHR cha nges.
Keywords: Labour Analgesia, Foetal Heart Rate
Changes, Epidural Analgesia, Combined Spinal Epidural,
Intravenous Ana l ges i a
Foetal well-being during labour is of utmost importance.
One of the ways to attempt to determine foetal well-
being is by recording foetal heart rate (FHR). Loss of beat
to beat varia bility and deceleration patter ns are known to
be associated with foetal distress. Gynaecological factors,
maternal and foetal factors, but also anaesthesiological
factors can influence these FHR tracings. Decelerations
and foetal bradycardia have been described after all types
of effective labour analgesia (epidural, spinal and Com-
bined Spinal Epidural (CSE), and intravenous opioids).
Early descriptive reports were conflicting. Lieberman
et al. [1] compared intramuscular meperidine to epidural
bupivacaine and only detected significant FHR changes
in parturients with hypotension or uterine hyper stimu-
lation. In contrast, Boehm et al. who studied epidural li-
docaine with or without epinephrine, found that 53%
(eight patients) revealed a reduction in FHR variability
without indication of the exact mechanism [2]. Later
studies failed to demonstrate these effects of epidural li-
docaine with or without epinephrine [3,4]. Unfortunately
these studies are difficult to interpret because of a lack o f
randomization, small sample sizes and inconsistent dose
This mini-review provides a comprehensive intrapar-
tum data on FHR effects of a multitude of analgesic
regimens which makes it different from previously pub-
lished repor ts. It attempts to address the questions if cer-
tain techniques and/or analgesics lead to clinically rele-
vant FHR changes, such as loss of baseline variability,
late decelerations or severe variable deceleration patterns,
what is their aetiolog y, and how we should manage these
FHR changes.
A MEDLINE-based search of all the literature on FHR
changes due to labour analgesia was performed. The
following keywords were used: labour analgesia; foetal
heart rate changes; epidural analgesia; combined spinal
epidural; intravenous analgesia; and acupuncture. No
date or language restriction was used. The reference lists
of retrieved articles were searched by hand. Articles that
did not report on the FHR outcomes were excluded. In
this mi ni -re vi ew, no meta-analysis was performed.
Continuous epidural analgesia is commonly used for
analgesic treatment during labour and delivery as it ef-
fectively relieves labour pain. In reviewing the literature
many r epo rts a bo ut change s in F HR in la bour ing p ati ents
with epidural analgesia were found. Historically abnor-
mal FHR patterns have been found to be most common
when epidural analgesia was accompanied by maternal
hypotension [5], or supine position of the parturient [6].
Stavrou et al. [7] conducted a retrospective study trying
to find a relationship betwee n prolonged foetal bradycar-
dia and epidural analgesia during labour. They concluded
that administration of epidural analgesia is associated
with episodes of prolonged foetal bradycardia, as they
found that prolonged bradycardia (defined as a fall in
N. M. A. A. Engel et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 113-120
Copyright © 2011 SciR es. OJOG
FHR at least 50/ min belo w baseline and lasting at least 3
minutes) developed in 40 of 366 (11%) of parturients
with epidural analgesia. These FHR changes were not
accompanied by maternal hypotension (hypotension oc-
curred only in one patient) and FHR returned to normal
in all patients. Most episodes of foetal bradycardia oc-
curred within 20 minutes of local anaesthetic administra-
tion. Neonatal outcome was not influenced.
Another retrospective comparative study between pa-
tients with and without epidural analgesia showed sig-
nificant differences in variable decelerations and late
decelerations in FHR tracing before and after institution
of epidural analgesia. An increase in variable and late
decelerations was observed after injection of the main
dose of epidural analgesic. Twenty four percent of car-
diotocograph tracings (CTGs) showed variable decelera-
tions before, and 35% showed decelerations after epidu-
ral analgesia [8]. Neonatal outcome was similar in both
groups. As mentioned by the authors, groups were per-
haps not comparable as the epidural group contained
more primipara, more frequent induction of labour, first
and second stages of labour were longer (possibly an
effect of the epidural) and the duration of ruptured mem-
branes was longer. The authors suggest that these FHR
changes might be attributed to direct effects of the local
anaesthetic on the foetus. However, Phillips et al. [9]
studied PR interval, RR interval, T/QRS ratio and the
PR-RR correlation coefficient using foetal electrocardio-
gram waveform analysis during epidural analgesia with
bupivacaine and found a significant increase in FHR and
a fall in T /QRS ratio. Their c onclusion was that epidural
bupivacaine does not alter foetal myocardial conduction
as measured by PR interval nor does it induce ischemic
cardiac changes as assessed by the T/QRS ratio. Thus the
FHR c han ges o ccur rin g dur in g epi dura l ana lge sia a re no t
caused by a direct depression of the foetus by bupiva-
Durin g the last fifteen years, the ad dition of opioid s to
local anaesthetics for epidural analgesia has become in-
creasingly popular because it offers the advantage of re-
duction of the local anaesthetic dose with faster onset of
analgesia and resulting in the same amount of analgesia
than with local anaesthetics alone [10]. Dose reduction of
local anaesthetic results in less motor blockade which
can allow for ambulation during labour, and may reduce
the risk of dystocia and caesarean section. Purported ad-
vantages of ambulation consist of increased intensity of
contractions, less pain, shorter first stage of labour, and
patient’s appreciation of mobility [10]. Studies on the
effect of ambulation on labour have not shown any det-
rimental effects [11,12]. Hoffman et al. studied the ef-
fects of continuous opioid epidural on FHR but without
letting the parturient ambulate. They discovered that
there are no significant differences between opioid and
non-opioid epidurals with respect to maternal blood pre-
ssure, FHR tracings, and neonatal outcome [10]. These
results were confirmed by a double blind, randomized,
controlled study, by Amant and co-workers [13], 109
parturients who received bupivacaine 0.25% with addi-
tion of either b uto r phanol, fentanyl, sufentanil or saline.
Prophylactic administration of ephedrine to prevent
maternal hypotension and FHR changes has also been
studied. In a prospective randomised trial by Kreiser et al.
[14], 145 parturients were scheduled to either receive
ephedrine 10 mg i.v. bolus followed by a continuous in-
fusion of 20 mg i.v. during one hour at time of initiation
of the epidural analgesia, or no prophylactic ephedrine.
FHR monitoring was used during the first 40 minutes
after anaesthetic administration. The analgesic dose in
this study was relatively high (3 ml of 2% lidocaine for
initiation, follo wed by 8 ml of b upivacaine 0.25%). FHR
changes occurred in 2 out of 72 treated patients and in 11
of 73 controls. In another randomised trial Cleary-
Goldman et al. [15] studied the effects of intramuscular
ephedrine 25 mg versus placebo in 100 parturients
treated with CSE analgesia. Significantly fewer women
in the ephedrine group developed hypotension. There
were no differences in FHR decelerations in the hour
following initiation of analgesia. There was however an
increased risk for development of foetal tachycardia in
the group treated with ephedrine.
Prophylactic use of ephedrine does not seem indicated
for low dose labour analgesia (“walking epidural”). Con-
tinuous infusion of ephedrine is not recommended be-
cause it has been associated with foetal acidosis in cases
of elective caesarean section [16].
Studies conducted on epidural opioids alone gave dif-
ferent results. Capogna and co-wor kers [17] conducted a
prospective, sequential allocation study to determine the
minimum effective concentration of epidural sufentanil
in spontaneous and induced labours. A transient reduc-
tion (mean 30 minutes) of FHR long-term variabilit y was
found in 53% of spontaneous and in 63% of induced
labours within 10 minutes of administration of epidural
sufentanil 18 µg - 32 µg. All FHR changes resolved
sponta- neously. According to the authors one explana-
tion for these FHR changes could be a direct depressant
effect of opioids as was determined for morphine and
pethidine by Petrie et al. [18]. Although epidural sufen-
tanil i n therapeutic doses (10 µg - 30 µg of sufentanil in
the epidural mixture) is detectable in the maternal circu-
lation [19], it seems unlikely that these low doses used
for epidural analgesia have any important systemic im-
pact [19,20].
Combined spinal epidural (CSE) analgesia has become
N. M. A. A. Engel et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 113-120
Copyright © 2011 SciR es. OJOG
increasingly popular as a met hod for labour pain relief as
it has a very rapid onset of analgesia. FH R cha nges have
been observed with intrathecal analgesia using small
doses of local anaesthetic or opioids, alone or in combi-
At first, the increase in variable decelerations noted in
a prospective, double blind, comparative study among
intrathecal fe ntanyl, meperidine, a nd sufentanil b y Honet
et al. [21], was deemed to be of little clinical signifi-
Two years later however Clarke and co-workers re-
ported several episodes of uterine hyperactivity in some
cases associated with foetal bradycardia following in-
trathecal administration of 50 µg of fentanyl [22]. A de-
crease in foetal heart rate to 80 - 100 beats/min was
noted in 7 of 30 consecutive patients. In two other pa-
tients the foetal heart rate decreased below 70 beats/min.
These FHR alterations occurred without maternal hy-
potension and all appeared within 30 minutes after in-
trathecal injection of fentanyl. Five out of the nine pa-
tients with foetal bradycardia also exhibited uterine hy-
peractivity detected by external or internal pressure
transducer. This uterine hyperactivity following intrathe-
cal fentanyl has since been confirmed on several occa-
sions [23-25].
Yet there is no agreement about the association be-
tween uterine hyperactivity and non-reassuring FHR
patterns caused by spinal opioids.
Gambling et al. [26] conducted a large randomized
trial comparing i.v. meperidine with CSE (with intra-
thecal sufentanil 10 µg) and reported FHR decelerations
in 18% in the CSE group compared to 21% in the me-
peridine group. However bradycardia necessitated cae-
sarean section in 8 out of 400 women with CSE com-
pared to 0 out of 352 mothers in the meperidine group.
Cautious interpretation of these results is necessary. The
mothers who received i.v. meperidine had intermit ten t
FHR monitoring, while the mothers with CSE had con-
tinuous monitoring of FHR for at least 30 minutes after
intrathecal injection. Furthermore these results are not
corroborated by later studies. Eberle and co-workers con-
cluded that the risk of prolonged foetal deceleration after
epidural bupivacaine or intrathecal sufentanil labour an-
algesia is unrelated to analgesic technique [27]. Fogel et
al. also failed to demonstrate significant differences in
the incidence of new prolonged decelerations or late de-
celerations between epidural and CSE analgesia [28].
In a prospective study by Nielsen et al. [29] a compa-
rison was made between the incidence of intrapartum
FHR abnormalities and obstetric outcome after epidural
bupivacaine and intrathecal sufentanil. The authors con-
clude that in b oth gro ups the re was a signi ficant ly highe r
risk of caesarean section in patients who’s previously
normal FHR tracing became abnormal after analgesia
when compared to patients without a new onset FHR
abnormality. These new onset FHR abnormalities might
be due to a pre-existing problem. However intrathecal
sufentanil was not associated with a higher incidence of
new onset FH R abnormalities.
In a review article by Norris [30], the author concludes
that there is insufficient evidence to accept that spinal
opioids are responsible for a more frequent occurrence of
new FHR abnormalities when compared to conventional
epidural analgesia.
On the other hand there are reports by Van de Velde et
al. [31] who performed a retrospective analysis on the
FHR effects by sufentanil 7.5 µg intrathecally, compared
to conventional epidural and compared to sufentanil 1.5
µg intrathecally during CSE. They conclude that sufen-
tanil in a dose of 7.5 µg has the potential to result in
more non-reassuring foetal heart rate tracings compared
to both other groups.
A systematic review of intrathecal opioids compared
with other neurax ial tech niques co ncluded that despite a n
increased risk for foetal bradycardia: odds ratio 1.8 (95%
confidence interval 1.0 to 3.1) the risk for subsequent
caesarean section is not increased [32].
More recently Abrao and co-workers [33] performed a
randomized controlled trial on 77 parturients to estimate
the effects of combined spinal-epidural and traditional
epidural analgesia on uterine basal tone and its associa-
tion with the occurrence of FHR abnormalities. This is
the only study in wh ic h i ntr a u te r ine p r es s ure was d ir ec tl y
prospectively measured. Patients in the CSE group re-
ceived bupivacaine 2.5 mg plus sufe ntanil 2.5 µg. In the
epidural group patients received bupivacaine 12.5 mg of
a 0.125% solution plus of sufentanil 10 µg. The type of
analgesia was shown to be the only independent predi-
ctor of uterine hyper tonus. The authors concluded that
CSE is associated with a significantly greater incidence
of FHR abnormalities related to uterine hyper tonus
compared with epidural a nalge sia, but thi s did not le ad to
a higher incidence in caesarean section.
In comment of this study by Abrao and co-workers
[33], Landau et al. [34] state that the two analgesic regi-
mens used in this study may not be equipotent as shown
by the higher pain scores in the epidural group compared
to the CSE group. Also the slower onset of pain relief
with epidural analgesia makes it likely that FHR and
intrauterine tone changes only become apparent after the
study period of fifteen minutes. This may have exagge-
rated the differences reported between study groups.
Landau et al. also comment on the late initiation of la-
bour analges ia in this study (6 cm cervical dilation) as it
is known that neuraxial analgesia in this stage of labour
is more commonly associated with FHR abnormalities
N. M. A. A. Engel et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 113-120
Copyright © 2011 SciR es. OJOG
than when it is initiated earlier [35]. FHR changes and
abnormalities may also be influenced by parity and use
of oxytocin which are not adequately detailed in the
study by Ab rao and co-workers [33].
The 2.5 µg of sufent anil fo r int rathecal ana lgesia in the
study by Abrao et al. [33] is also substantially higher
than the dose in group 2 used earlier by Van de Velde and
co-workers [36] in a double-blind, double placebo-con-
trolled trial comparing two forms of CSE with epidural
analgesia. In this study a comparison was made between
epidural bupivacaine 12.5 mg plus 7.5 µg sufentanil 7.5
µg wit h epinep hrine 1 2.5 µg, intrathecal bupivacaine 2.5
mg pl us sufe ntani l 1.5 µg with ep inephri ne 2.5 µg, and a
third group with sufentanil 7.5 µg intrathecally. Twenty
four % of the patients in the high dose intrathecal sufen-
tanil group developed FHR abnormalities compared to
11% in the lower dose intrathecal sufentanil and 12% in
the epidural group. Uterine hyperactivity occurred in
12% of the high dose intrathecal sufentanil group com-
pared to 2% in the other two groups, but tocolytic the-
rapy was rarely needed.
The data from these recent studies warrant caution in
the use of higher doses of opioids intrathecally because
of the risk of uterine hyperactivity and FHR abnormali-
ties, without however increasing the risk for caesarean
delivery or detrimental effects o n neonatal outcome.
One study has been done with addition of intrathecal
tramadol to CSE analgesia. Since there is no human
toxicolog y a vailable for intrathecal ad ministratio n of tra-
madol, such studies ethically need to be conducted under
specific approval from the appropriate government
source. Frikha et al. [37] conducted a randomized pro-
spective study comparing bupivacaine 2.5 mg with su-
fentanil 2.5 µg to bupivacaine 2.5 mg with tramadol 25
mg intrathecally. The purpose of this study was to com-
pare tramadol and sufentanil in terms of duration of an-
algesia and frequency of adverse maternal or foetal ef-
fects. FHR tracings of all patients were done from one
hour before analgesia to one hour after initiation of an-
algesia. All FHR tracings were normal before initiation
of CSE. FHR tracings after initiation of analgesia were
comparable between the sufentanil and tramadol groups.
No patient in this study had a non-reassuring FHR trac-
ing. The group of patients receiving tramadol had sig-
nific antl y longer-la s ting a nalgesia. Five of the 2 0 patients
receiving tramadol also presented with vomiting, which
is the only major side effect noted with tramadol in this
Neuraxial analgesia has become the ‘gold standard’ for
obstetric analgesia. Unfortunate ly it ca nnot b e us ed in a ll
parturients, e.g. tendency towards bleeding, spinal de-
formities, spinal instrumentation, and patient refusal. In
these cases alternatives need to be explored for pain re-
Pethidine is most widely used for labour pain analge-
sia because of familiarity and low cost, although the ef-
ficacy of pethidine has been questioned. Pethidine has
been shown to significantly affect FHR variability, ac-
celerations and decelerations, during labour [38]. No
significant differences in FHR changes were shown be-
tween pethidine and epidural analgesia [39].
Long et al. [40] studied tramadol patient controlled
analgesia (PCA) compared to CSE with patient con-
trolled epidural analgesia and a control group without
analgesia for comparison of risks and benefits. CSE an-
algesia resulted in faster onset and better pain relief than
PCA with tramadol. There were no differences in FHR
and uterine contractions among the three groups. The
authors concluded that PCA with tramadol is a useful
alternative to CSE but may be accompanied by newborn
depression as Apgar scores were lower in the tramadol
The reported analgesic properties of systemic opioids
in labour are poor, but PCIA has proven to have phy-
chological benefits, and when used with remifentanil
allows for very rapid d rug titration. [41 ] .
The reported use of remifentanil for labour pain anal-
gesia in the literature have described various methods of
administration with inconsistent results. Mostly remifen-
tanil is used i n PCA setting, with or without a basal in fu-
sion. In one study by D’Onofrio et al. 205 parturients
received a continuous infusion of remifentanil without
PCA to examine analgesic effect, patient satisfactio n and
maternal and neonatal safety of this method of admini-
stration [42]. Infusion rates varied between 0.025 µg/kg/min
– 0.15 µg/kg/min. Oxygen saturation remained above
95% at all times without oxygen supplementation. No
changes in FHR variability score were detected, and dur-
ing the 30 minute study period moderate analgesia was
observed with good patient satisfaction.
PCA wit h remifenta nil compar ed to ep idural levobupi-
vacaine with fentanyl was studied in a randomized con-
trolled, double-blinded trial [43]. This study concluded
that analgesia with epidural is superior, sedation was
more common in the remifentanil group and the number
of parturients with nausea was larger in the remifentanil
group. The groups were not different in terms of abnor-
malities in FHR tracings.
However, d iscussion remains about safety and efficacy
of PCA with remifentanil. Labour pain analgesia by re-
mifentanil is modest and the risk for maternal sedation
and oxygen desaturation even in the presence of oxygen
supplementation remains [43]. On the other hand, PCA
with pethidine has an even higher risk for oxygen de-
N. M. A. A. Engel et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 113-120
Copyright © 2011 SciR es. OJOG
saturation [44]. Less FHR changes have been reported
using PCA remifentanil as compared to PCA pethidine
[44]. Hill [45] performed a retrospective analysis of 5410
consecutive deliveries. 28% PCA remifentanil, 22% epi-
dural analgesia and 33% intramuscular pethidine analge-
sia with similar neonatal outcomes in all three groups.
Van de Velde [46] on the other hand argues that remifen-
tanil crosses the placenta readily and causes foetal im-
mobil it y (duri ng i n utero surg ery) and los s of foetal heart
rate variability. He concludes that routine use of PCA
with remifentanil cannot be promoted before extensive
studies have been done to evaluate the effects of remi-
fentanil on foetus and neonate [46].
As many women like to avoid invasive and/or pharma-
cological methods of pain relief during labour sometimes
acupuncture is recommended. The evidence on acupunc-
ture remains unclear. Acupuncture seems to have no de-
trimental effects on FHR. In one study there seemded to
be a reduction of foetal baseline heart rate and more ac-
celerations were observed during acupuncture [47]. In
another study by the same group the foetal heart rate was
reduced only by acupuncture and moxibustion combined
In a study of moxibustion alone cardiotocograms were
made 10 minutes before, 20 minutes during and 10 mi-
nutes after each session and there was no alteration or
abnormality detected [49]. Cochrane review concludes
that acupuncture and acupressure may have a role in re-
ducti on o f pain d uring l abour, but t here i s a nee d for fur-
ther research [50].
Several hypotheses have been proposed in the literature
as to the origin of the FHR changes and foetal bradycar-
dia observed with effective labour analgesia. In 1971 a
comparison was made between FHR changes and pH of
foetal blood. Decelerations and a loss of beat-to-beat va-
riability appeared to be associated with foetal acidosis
and therefore foetal asphyxia [51]. Huovinen et al. [6]
found a higher incidence of FHR changes in the supine
position when co mpared to latera l position. P reston et al.
[52] reported a 15% incidence of severe FHR changes in
parturients in supine wedged position compared to the
left lateral position. These changes were attributed to
occult aortocaval compression. This was contradicted by
Eberle and co-workers [27] who found that prolonged
decelera tions were not related to maternal p osition, but 8
of the 11 episodes they noted were associated with uter-
ine hyper tonus or tetany.
Segal and co-workers [53] used gravid rat uteri to
show that epinephrine and norepinephrine have effects
on uterine tone. Epinephrine caused dose dependent re-
ductions in uterine activity. Norepinephrine alone in-
creased uterine activity. Maternal epinephrine levels de-
cline after effective labour analgesia but norepinephrine
level s remain relativel y unchanged.
Four years earlier Clarke et al. [22] proposed the fol-
lowing mechanism for foetal bradycardia following an-
algesia: Pain relief leads to a decrease in output of the
sympathetic nervous system (effective labour analgesia
leads to a decrease in circulating epinephrine levels).
Epinephrine is a tocolytic. Decreasing epinephrine will
cause an increase in uterine tone which will decrease
placental blood flow. If placental blood flow is decreased
enough there will be a subsequent foetal bradycardia.
Cascio et al. [54] also noted a reduction in maternal
plasma epinephrine concentrations following both epi-
dural and spinal analgesia, while plasma norepinephrine
stayed the same or even increased slightly. They also ob-
served faster decrease in plasma epinephrine in partu-
rients who received spinal opioids when compared to
epidural bupivacaine, which offers a possible explanation
for the fast er onse t of FHR c hanges i n CSE co mpared to
epidural analgesia. The mechanism by which higher
doses (fentanyl 25 µg - 50 µg [23,25], sufentanil 7.5 µg
[31]) of intrathecal opioids more often lead to FHR
changes remains unclear.
There are few data to determine the impact of epidural
analgesia on pre-existing FHR abnormalities. Most stu-
dies exclude these patients. Fogel et al. [28] included 30
patients with FHR abnormalities pre-analgesia. In most
cases these FHR abnormalities persisted.
Regardless of the aetiology of the FHR abnormalities,
the key is managing these changes correctly when they
occur. In all of the studies reviewed the incidence of FHR
changes is relatively high, 3 % - 20% [25,27,28], but this
does not lead to higher incidence of caesarean section.
Caesarean section is probably avoided by adequate tr-
eatment of these FHR changes. The use of uterine dis-
placement and changing maternal position to relieve any
aortocaval compression. Correcting any hypotension
using phenylephrine in 50 µg - 100 µg increments (or
ephedrine in 5 mg - 10 mg increments) and intravenous
fluids. Giving extra oxygen. Stopping administration of
oxytocin because of the association of FHR change s with
uterine hyper stimulation. Administration of a tocolytic
agent should be considered [20,55]. Uterine hyper tonus
may be reversed by intravenous nitro-glycerine 60 µg -
90 µg, to be repeated when hyper tonus remains [56].
N. M. A. A. Engel et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 113-120
Copyright © 2011 SciR es. OJOG
Nitro- glycerine reduces uterine contractility by raising
intracellular cyclic Guanosine Monophosphate (cGMP)
whic h in turn inactivates myosin light-chain kinase. One
can also relax the uterus by terbutaline 0.25 mg i.v. but
this causes a much longer relaxation of the uterus com-
bined with maternal tachycardia because of action on
beta-2-receptors. Activation of beta-2-receptors leads to
inhibition of myosin light-chain kinase resulting in re-
laxation of the uterine muscle. Effective treatment of
uterine hyper stimulation allows for normalisation of
uterine and placental perfusion, and thus for normalisa-
tion of FHR tracings.
From the available literature we conclude that induction
of labour analgesia can result in FHR cha n ges and se ve r e
foetal bradycardia. Most likely this is due to uterine hy-
per tonus secondary to an acute drop in plasma levels of
epinephrine. As higher doses of intrathecal opioids seem
to be related to more frequent non-reassuring FHR trac-
ings, administration of high doses of intrathecal opioids
(≥7.5 mcg sufentanil) is best avoided.
Mechanisms of action for this high dose opioid effect
are unknown. Many other factors may be related to FHR
changes after labour analgesia. Further research on the
different factors influencing FHR changes during labour
analgesia is needed, as well as research directed at clari-
fying the specific mechanism of action of “high” doses
of intrathecal opioids on FHR. Only then can prevention
of FHR changes after labour analgesia be achieved.
When F HR c hange s o ccur it is of vital importance that
the parturient is treated immediately. FHR changes are
not an uncommon effect of effective labour analgesia but
should not affect the outcome of the delivery or neonatal
The authors declare that they have no competing interests, and that
there was no funding for this review art ic le.
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