ISnUdNiaAnN JD. AAn, aAeNstAhN. 2D0,0 H6;E 5M0 E(5S)H : 3: 6A3C - U36T9E PAIN ? LABOUR ANALGESIA 363
1. M.D., Ph.D., MNAMS, Prof.
2. M.B.B.S., Sr. Registrar
3. M.B.B.S., Sr. Registrar
Dept. of Anaesthesiology and Pain Management,
RNT Medical College, Udaipur, Rajasthan
Correspond to :
Sunanda Gupta
Dilshad Bhawan, 69 Chetak Circle
Udaipur - 313001, Rajasthan-India
E-mail : [email protected]
Dr. Sunanda Gupta1 Dr. GS Anand Kumar2 Dr. Hemesh Singhal3
Keywords : Labour analgesia.
Labor is characterized by regular, painful uterine
contractions that increase in frequency and intensity and
are associated with progressive cervical effacement and
dilatation. Labour has been divided into three stages. The
first stage occurs from onset of cervical change to
10 cms dilatation. It can be divided into latent and
accelerative phases. The latent phase can last up to 8 hrs,
without the need of intervention, while the active phase is
associated with a faster rate of cervical dilatation and
usually begins at 2-4cms dilatation and the duration varies
from 2 to 6hrs. The second stage occurs from full cervical
dilatation (10 cm) to delivery of the baby. Normally the
second stage lasts for 2 hrs (3 hrs with regional anaesthesia)
in a primipara and 1 hr (2 hrs with regional anaesthesia)
in a multipara. The third stage occurs from delivery of the
baby to separation and expulsion of placenta and the
Pain pathways
Mechanism of labour pain (table 1)
Perception of pain during the first stage of labour
begins with nociceptive stimuli arising in the mechanical
and chemoreceptors in the uterus and cervix.1 High threshold
mechanoreceptors get stimulated due to intense pressure
generated during contractions of the uterus.2 Myocellular
injury due to repeated contractions in later stages, release
bradykinin, histamine, serotonin, acetylcholine and potassium
ions which activate chemical nociceptors.3
a. Peripheral pathways
I stage of labour: Pain of the first stage of labour is
due to uterine contractions and stretching of the
cervix. It is cramping and visceral in nature, diffuse
and poorly localized. Sensations are carried through Ad
and C primary afferent fibres which pass sequentially
through the inferior, middle and superior hypogastric
plexus, the lumbar and lower thoracic sympathetic
chain and end in rami communicantes associated with
T10-L1 spinal nerves. (fig. 1)1 It is predominantly carried
by the C fibres.
Table - 1 : Labour pain: Pathways and mechanisms.3
Site of Mechanism Pathway Site of
origin action
Uterus, Distortion, Afferents which accompany Upper
Cervix Stretching, sympathetic pathway to abdomen &
Tearing of T10-L1Dorsal rami T10-L1 groinmid-back
Fibres refer to cutaneous branches
of posterior divisions
Periuterine Pressure often Lumbosacral plexus L5-S1 Low back, thigh
tissues in association (?pelvic splanchnic nerves)
Lumbosacral with fetal
region malposition or
platypelloid pelvis
Bladder, Pressure by S2-S4 Referred to
urethra, presenting part perineum and
rectum sacral area
Vagina Distension, Somatic S2-4 Not referred
Perineum Distension, Pudendal (S2-4); Not referred
tearing Genitofemoral (L1-2);
Ilioinguinal (L1)
Posterior cutaneous
nerve of thigh (S2-3)
Bladder Overdistension Afferents which
accompany sympathetic Suprapubic
pathway to T11-L1
Fig. 1. : Peripheral neural pathways associated with labour pain.1
The uterus. including the cervix and lower uterine segment. is supplied by afferents
that pass from the uterus to the spinal cord by accompanying sympathetic nerves
through the inferior hypogastric plexus (1HP). the hypogastric nerve, the superior
hypogastric plexus (SHP). the lumbar and lower thoracic sympathetic chain. and the
nerves at T10. T11. T12. and L1.
II stage labour : During the late first and second
stage of labour, somatic pain predominates, as a result of
distension and traction on the pelvic structures, the pelvic
floor and the perineum and is carried via the pudendal
nerve (table 1)3 through the anterior rami of S2 through S4.
Unlike visceral pain of first stage, it is sharp and well
localised, due mainly to less arborization and the faster
conduction velocity in the sacral pathways. It is
predominantly carried by the Ad fibres.4
b. Central pathways
The pathways labor sensation travels after entry into
the central nervous system includes both the ascending and
the descending pathways.
Ascending pathways
The first synapse in the pathways occurs in the dorsal
grey matter of spinal cord (Rexed?s Laminae I
to V). Most of the primary afferent neurons synapse
initially in the more superficial laminae I and II
(substantia gelatinosa); locally projecting interneurons in
turn synapse on the more deeply located wide dynamic
range (WDR: lamina V) neurons. The WDR neurons
receive synaptic excitatory input from both the large
myelinated A? and A? mechanoreceptor afferents and C
polymodal nociceptive afferents. The fact that all of the
lamina V cells which respond to visceral high threshold
afferents also respond to low threshold cutaneous afferent
from an area of skin supplied by the same spinal cord
segments is important. Thus the lamina V cells provide
the neural basis for the phenomenon of referred pain which
occurs during each uterine contraction. (fig. 2)
analysis occurs, and to the hypothalamic and limbic systems,
where emotional (affective) and autonomic responses
Fig. 2 : Intensity and distribution of parturition pain during
the various phases of labour