Normal & Abnormal Uterine Action

Anthony Alexander

Normal Uterine Action• Multiple factors initiate uterine action– Hormonal– Non-hormonal

Hormonal Factors• Oestrogen

– Increased free oestrogens in the last trimester increase uterine excitability• Progesterone

– Prior to labour, there is a drop in progesterones. This augments the oestrogen induced excitability.

• Cortisol– Produced by the foetal adrenal gland . Works by increasing the oestrogen

production of the placenta• Prostaglandins

– Prostaglandins E2 and F2α are powerful stimulators of uterine muscle activity. PGF2α was found to be increased in maternal and foetal blood as well as the amniotic fluid late in pregnancy and during labour.

Non-hormonal Factors• Uterine distension• Stretch of the lower uterine segment by the

presenting part

Physiology• By the end of pregnancy, the factors which favour uterine

contraction outweigh those which resist it• The uterus, like other smooth muscle organs, exhibits

waves of contractions beginning at the fundus, downwards to the lower segment.

• Contractions of the uterus are paralleled with cervical dilatation. The increased frequency and intensity of uterine contractions will cause descent of the presenting part with progressive cervical dilatation and effacement.

The Contractions• Begin in the cornu of the uterus• Travel as a wave which takes 10-30 seconds to

spread out over the whole uterus• Upper part contracts more strongly and longer

than the lower part• The dominance of the upper segment leads to

stretching and thinning of the lower segment, and dilation of the cervix

Post Delivery of Foetus• After seperation of the placenta, the uterine

muscle fibres contract occluding the blood vessels that supplied the placenta, thereby reducing blood loss.

Abnormal Uterine Action

Abnormal Uterine Action

Uterine Overactivity

Precipitate Labour

Obstructed Labour

Uterine Underactivity

Hypertonic Inertia

Hypotonic Inertia

Cervical Dystocia

Uterine Overactivity

Precipitate Labour• Describes labour lasting for less that 3 hours• Due to– Strong coordinate contractions of the uterus– Small foetus– Absence of obstruction of the birth canal and

resistance from soft tissue• Patient often only feels last contractions of

labour

Diagnosis• Often a retrospective diagnosis• If seen in the 1st stage of labour, partogram

will show progressive cervical dilatation and effacement

Complications• Maternal: – Lacerations of the cervix, vagina and perineum. – Shock. – Inversion of the uterus. – Postpartum haemorrhage: due to lacerations or

limited time for retraction – Sepsis secondary to lacerations

Complications• Foetal: – Intracranial haemorrhage – Foetal asphyxia due to: • strong frequent uterine contractions reducing placental

perfusion, • lack of immediate resuscitation.

– Avulsion of the umbilical cord.

Management• Prophylaxis– Patients with history of precipitous labour should be

admitted at first contraction• If seen during delivery– Consider nitrous oxide and oxygen anaesthesia and

sedation to prevent forcible bearing down• After delivery– Exploration of birth cavity to manage injuries which may

have occured

Management• Prophylactic antibiotics if delivery in

unfavourable environments• Examination of fetus to detect injuries

Obstructed Labour• Describes excessive uterine contractions and retraction

in the presence of obstruction• In an effort to overcome the obstruction, there is

marked retraction of the upper segment, accompanied by thinning of the more passive lower segment

• Retraction ring (Bandl ring) rises up and can be seen through the abdomen

• If untreated, the thinner lower segment may rupture

Uterine Underactivity

Hypotonic Inertia• Weak, innefficient and infrequent uterine

contractions

Associated Factors - General• Primigravida, especially elderly• Anaemia and chronic illness• Inappropriate use of analgesia• Nervous/anxious mother• Hypertensive states in pregnancy

Associated Factors- Local• Developmental abnormalities of the uterus

(e.g. bicornuate)• Uterine fibroids• Uterine overdistension• Induction of premature labour• Malpresentation/malposition

Clinically• Labour is prolonged: at various stages of labor

(detected clinically by partogram as e.g.: prolonged latent phase, protraction disorders and arrest of cervical dilatation).

• Uterine contractions are weak, infrequent and have short duration. This can be detected clinically by: – On palpation: weak increase in uterine tone, less than 3

contractions in 10 mins, each less than 30s long– Tocodynamometer

Maternal Complications• In the 1st stage:

– Nervousness, anxiety, exhaustion and starvation ketoacidosis• In the 2nd stage

– Prolongation, increased liability for instrumental delivery and C/S

• In the 3rd stage– Placental retention aand PPH– Subinvolution of the uterus– Risk of abuse of uterine stimulants

Foetal Complications• Minimal except infection from prolonged

premature rupture of membranes

Management• General– Ensure that the patient is actually in labour and

not in the prodrome of labour– Rule out CPD– Manage stage 1 of labour as follows

Management • Specific– Oxytocin drip– Operative management:• Mechanical rupture of membranes• Forceps delivery: if fully dilated cervix• C/S: if foetal distress occurs before full cervical

dilatation

Hypertonic Inertia• Excessive but uncoordinated uterine activity• Results in failure to progress• Two types:

– Colicky uterus: incoordination of the different parts of the uterus in contractions.

– Hyperactive lower uterine segment: so the dominance of the upper segment is lost

The Clinical Picture• Labour is prolonged• Uterine contractions are irregular and between the

contractions the uterus is not lax, with increased basal tone

• Contractions are painful, the pain preceeding and outlasting the contraction. There is marked lower backache

• Slow cervical dilation and effacement • Early rupture of membranes

Treatment• General– Exclude disproportion, malposition and

malpresentations– Proper management of the 1st stage of labour

Treatment• Medical– Analgesics and antispasmodics (e.g. hyoscine).

Consider epidural if patient doesn’t respond to analgesics

• Surgical– C/S if analgesia fails to call normal uterine action

and progressive cervical dilatation

Constriction Ring• Persistent localised annular spasm of the

unterine muscles• Can occur at any stage of labour• Can occur at any part of the uterus but

junction of the upper and lower segments commonly

Aetiology• Unknown but:– Malpresentations and malposition– Rough or repeated intrauterine manipulation– Improper use of uterine stimulants

Treatment• Exclude disproportion, malpresentations and malposition.• Analgesics e.g.: pethidine and antispasmodic e.g. hyoscine.• In the 2nd stage, give deep general anesthesia and amyl nitrite

inhalation then deliver the fetus immediately by forceps.• If the forceps fails or if the ring is below the presenting part,

cesarean section is needed.• In the 3rd stage, give deep general anesthesia and amyl nitrite

inhalation then remove the placenta manually in cases of hour glass contraction of the uterus.

Cervical Dystocia

Definition• Failure of cervical dilatation within a

reasonable time even in the presence of strong, regular uterine contractions.

Two Types• Organic– Due to fibrosis of the cervix due to previous

trauma• Functional– Non-dilation despite absence of organic lesions.

Lack of softening, or spasm due to excessive sympathetic tone

Clinically• External os felt as a hard rim

Complications• Those of prolonged labour• Rarely, annular detachment of the cervix

Treatment• Medical– In functional dystocia– Analgesia and spasmolytics

• C/S– If organic cause– In functional dystocia if

• Fetal distress especially with undilated cervix, and unengaged fetal head

• Medical management has failed

Conclusion• Efficient labour depends on regular and

coordinated uterine contractions• The management of abnormal uterine action

requires first excluding CPD, malpresentation and malposition

• Operative delivery is indicated in order to reduce complications of abnormal labour