ABNORMAL UTERINE ACTION

Introduction

Abnormal uterine action is one of the factors causing dystocia (difficult labor) in which uterine forces are insufficiently strong or inappropriately coordinated to efface and dilate the cervix (uterine dysfunction).

Pelvic contraction is often accompanied by uterine dysfunction and the two together constitute the most common cause of dystocia.

Similarly, malpresentation or large fetal size (macrosomia) may be accompanied by uterine dysfunction.

As a generalization, uterine dysfunction is common whenever there is disproportion between the presenting part of the fetus and the birth tract.

Physiology of uterine contractions: refer to normal labor

Uterine work can be evaluated using Montevideo units. Montevideo units are calculated by subtracting the baseline uterine pressure from the peak of uterine contraction pressure for each contraction in a 10 minutes window and adding the pressures generated by each contraction.

PHYSIOLOGICAL UTERINE CONTRACTIONS

The physiological control of myometrial activity takes place through estrogen, progesterone, oxytocin, prostaglandins, cyclic AMP, calcium, beta 2 receptors among others.

By the end of pregnancy, the balance of these factors is tipped, favoring an increase in uterine activity initiating labor.

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.

Assessment of uterine activity should include :FrequencyAmplitudeDuration Resting tone of the uterine muscle .

CLASSIFICATION OF ABNORMALITIES OF THE UTERINE ACTION:Uterine overactivity:Precipitate labor: in absence of obstruction.Obstructed labor: in presence of obstruction.Uterine underactivity: (uterine inertia): This may be due to:

1-Hypotonic inertia.2-Hypertonic inertia:

Uterus is hyperactive with increase in the basal tone with no or minimal effect on dilatation and effacement of the cervix, this may include the following types:

A-Incoordinate uterine contractions (colicky uterus): due to lack of synchrony of contractions of the myometrium.B-Hyperactive lower segment: due to lack of fundal dominance.

Contraction ring (constriction ring): caused by localized annular spasm of the uterine muscles.

3-Cervical dystocia.

UTERINE HYPERACTIVITY

1 .Precipitate labor:Definition:

It is a labor duration less than 4 hours due to strong coordinate uterine contractions in absence of obstruction in the birth canal, and resistance of the soft tissue, with small sized fetus. The patient does not feel except the last contractions during the expulsion of the fetus.

Diagnosis:

It is a retrospective diagnosis as the patient is usually seen in the 2nd or 3rd stages of labor. If seen during the first stage of the labor, the partogram will show rapid progress of cervical dilatation and effacement. If seen after delivery, examination of the mother and infant should be performed for the following

complications: Maternal:

*Lacerations of the cervix, vagina and perineum predisposing to: postpartum hemorrhage and sepsis which is also predisposed to due to delivery in unsuitable surroundings.

*Atony: due to uterine exhaustion may lead to postpartum *hemorrhage, retained placenta and inversion of the uterus.

*Shock due to heamorrhage and/or pain .

Fetal : *Intracranial hemorrhage: due to rapid compression and

decompression of the fetal head during delivery *Fetal injuries

*Avulsion of the cord *Neonatal sepsis

Management: Prophylaxis:

A patient with past history of precipitate labor should be admitted to the hospital at the first perception of labor pains.

Rarely if the patient is seen during delivery, general anesthesia (inhalation by nitrous oxide and oxygen or sedation) may be given to slow down the course of delivery to prevent forcible bearing down.

If the patient is seen after delivery: exploration of the birth canal for any injury and manage accordingly.

Prophylactic antibiotics if delivery occurred in unsuitable conditions

Proper examination of the fetus for detection of any complications.

2 .Excessive uterine contractions and retraction (in presence of obstruction) = uterine overactivity:

In obstructed labor, there is excessive uterine contraction in a trial to over come the obstruction, there will be marked retraction &thickening of the upper uterine segment while the more passive lower segment is markedly stretched and thinned to accommodate more and more of the fetus.

Therefore the retraction ring rises up and is seen and felt abdominally as a transverse groove that may rise to or above the

level of the umbilicus .This retraction ring is known as “pathological retraction ring or

Bandle ring .”Unless the obstruction is properly treated, the thinned out lower segment will rupture.

UTERINE UNDERACTIVITY1 .Hypotonic Inertia:

Definition: Weak, infrequent and ineffective uterine contractions

Etiology: Not known but the following factors may be associated:

1 .General factors : Primigravida especially elderly .

Anemia, chronic illness. (Antepartum hemorrhage leads to anemia that predisposes to inertia.

Hypertensive states with pregnancy.

Nervous, anxious patients. Improper use of analgesics.

2 .Local factors:

Overdistension of the uterus (e.g.: twins and polyhydramnios).

Anomalies in development of the uterus (eg: unicornuate, bicornuate and septate uterus).

Malpresentations and malposition

Full bladder or rectum.

Uterine fibroids: Fibroids interfere with proper uterine contractions.

Induction of premature labor.

Classification:

Primary inertia: Poor uterine contractions from the start of labor.

Secondary inertia: Uterine contractions become weaker after a period of

good uterine contractions due to uterine exhaustion in cases of cephalopelvic disproportion (act as a protective mechanism against rupture uterus).

Clinical picture:

Labor 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 :

Examination: On feeling the contractions abdominally there is weak increase in the uterine tone, uterine contractions in 10 minutes are less than 3 contractions and each lasting less than 30 seconds.

Monitoring using: External tocodynamometer: by external sensor over the abdomen.

The mother & the fetus are usually not seriously affected especially when the membranes remain intact, apart from prolonged labor.

If the inertia persists after delivery of the fetus, there is liability for retention of the placenta (prolonged 3rd stage of labor) and atonic postpartum hemorrhage.

Complications: Mostly that of prolonged labor

A. Maternal: In the 1st stage:

Nervousness, anxiety, exhaustion and starvation ketoacidosis. In the 2nd stage:

prolonged 2nd stage, increase liability for instrumental delivery and cesarean section.

In the 3rd stage:retention of the placenta and postpartum hemorrhageSubinvolution of the uterusRisks of abuse of uterine stimulants.

B. Fetal:Usually no effect apart from fetal infection from prolonged premature rupture of the membranes.

Treatment of Hypotonic inertia: General measures :

Proper diagnosis that this patient is in active labor (and not in the prodroma of labor) by proper identification of true labor pains (rhythmic, increase in strength, frequency and duration and accompanied by bulge of the bag of forewater and cervical dilatation.

Exclusion of cephalopelvic disproportion and malpresentations so as to be managed accordingly.

Proper management of the 1st stage of the labor:

Uterine stimulants:Oxytocin stimulation:

Aim:To increase the strength, frequency and duration of the uterine

contractions.Precautions before & during use of oxytocin:

There must be no contraindication to oxytocin. Exclusion of the following is essential:Cephalopelvic disproportion.

Malpresentations (however oxytocin can be given in cases of breech provided that the pelvis is adequate and there is no other contraindication).Incoordinate uterine action.Scar in the uterus.Grand multipara.Fetal distress.Multiple pregnancy.

Close observation of the mother &the fetal heart sounds by continuous fetal monitoring. If significant deceleration develops, stop the infusion.

Continuous automatic computer infusion pump: For proper calculation and adjustment of the dose.

Technique of I.V. oxytocin administration:Dissolve 5 units (5,000 mIU) in 500 ml of lactated ringer solution so 1 ml contains 10 mIU of oxytocin.

Assessment of efficiency of uterine contractions:a. Clinical:

The hand is applied on the patient's abdomen to detect frequency, regularity, duration and strength.b. External tocography:

A tocodynamometer is applied on the mother's abdomen to record uterine contractions.

Operative interference: Artificial rupture of the membranes: may be effective especially in

cases of hydramnios (will relieve the overstretch of the uterine muscles).

Operative delivery indicated if labor is prolonged beyond 24 hours or if there is fetal distress at any time.

One of the following may be done: Vaginal delivery for example by forceps if the cervix is fully

dilated and the conditions are suitable for vaginal delivery Caesarean section: if fetal distress occurs before full

dilatation of the cervix:

N.B.: continue the drip for at least one hour (duration of fourth stage) after delivery of the fetus to guard against retained placenta and atonic postpartum hemorrhage.

Secondary uterine hypotonia:this condition usually follows prolonged labor with good uterine contractions which has failed to overcome obstruction to delivery in

primigravida .Careful examination is needed to detect the cause of obstruction. CS is usually the solution.

2 .Hypertonic InertiaEtiology:

not known but the following may be associated:Anxiety.Repeated rough manipulation.Mal-use of oxytocin.Disproportion ,

malpresentations and malposition.

Clinical picture:Labor is prolonged (detected by partogram).

Uterine contractions are irregular and between the contractions the uterus is not lax with increase in the basal tone .

This can be detected by external tocodynamometer.Contractions are painful. The pain precedes, outlasts the contractions and there is marked low backache.

There is slow cervical dilatation and effacement (i.e. ineffective uterine contractions).

The membranes rupture early (due to increased intrauterine pressure).

Treatment:I. General measures:

Exclude disproportion, malposition and malpresentations (to be managed accordingly).Proper management of the 1st stage.II. Specific management:

1 .Medical:Analgesics e.g.: pethidine and antispasmodic e.g. hyoscine: Epidural analgesia may be useful in cases not responding to analgesics.

Normal uterine action with progressive cervical dilatation may occur following these measures.

2 .Caesarean section: is indicated in:In cases of disproportion.If fetal distress occurs before full cervical dilatation.

Cases in which analgesia fails to cause normal uterine action and progressive cervical dilatation.

CONTRACTION (CONSTRICTION) RINGDefinition:

It is a persistent localized annular spasm of the uterine muscles. It occurs at any stage of labor (1st, 2nd or 3rd stage).

It occurs at any part of the uterus but usually at the junction of the upper and lower segments.

Etiology :Not known but the following may be associated:

Malpresentations and malposition. Rough or repeated intrauterine manipulations (especially under light

anaesthesia) Improper use of uterine stimulants e.g. the use of oxytocin infusion in

hypertonic inertia.

Diagnosis:Contraction ring is frequently preceded by colicky uterus and the patient is usually a primigravida.

Contraction ring is only diagnosed by per vaginal examination i.e by feeling it with a hand introduced inside the uterus.

Contraction ring causes prolonged 2nd stage (as it usually lies opposite the neck of the fetus) .

It is suspected if there is prolonged 2nd stage without any obvious cause.

In the 3rd stage it may cause hour glass contraction of the uterus with retained placenta and postpartum hemorrhage.

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,

if the ring persists in spite of general aneasthesia, a vertical incision of the lower segment is needed to cut the ring.

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 .

Definition: This is a difficulty in labor due to failure of cervical

dilatation within a reasonable time in spite of the presence of strong, regular uterine contractions, i.e. no abnormalities in the uterine expulsive power.

CERVICAL DYSTOCIA

Types:1 .Organic rigidity (2ry):

Stenosis of the cervix by fibrosis following previous trauma or iatrogenic surgical trauma e.g.: cervical amputation, overcauterization, conization, repeated cerclage.

Organic obstruction of the cervix by cervical fibroid or carcinoma.

2 .Functional rigidity (1ry):It is non-dilatation of the external os of the cervix in absence of

any organic lesion .The process affects the external os only, so the cervix may be well effaced and the head is well applied to it.

Clinically:

The external os is felt as a hard rim.

Complications:

Besides the complications of prolonged labor and obstructed labor (if labor is neglected), very rarely annular detachment of the cervix may result.

Treatment: In cases of stenosis of the cervix by fibrosis, cesarean section is

the safest method of delivery if the cervix fails to dilate after a reasonable time.

In cases of organic obstruction of the cervix, cesarean section is the method of delivery.

In cases of functional rigidity:Giving time this cervix may dilate with good uterine contractions.

Analgesics as pethidine, and antispasmodics as hyoscine may be given.

If fetal distress occurs with the cervix less than half dilated or the head is not engaged cesarean section is done.

If fetal distress occurs with the cervix taken up and more than half dilated with the head deeply engaged: Cesarean section is the safe preferable solution.