Induction of labor
Uterine stimulants (uterotonics) are medications given to cause a woman's uterus to contract, or to increase the frequency and intensity of the contractions.
These drugs are used to induce or augment (speed) labor; facilitate uterine contractions following a miscarriage; induce abortion; or reduce hemorrhage following childbirth or abortion.
The three uterotonics used most frequently are:
oxytocins
prostaglandins
ergot alkaloids.
Uterotonics may be given intravenously (IV), intramuscularly (IM), as a vaginal gel or suppository, or by mouth.
PURPOSE:
Uterine stimulants are used to induce, or begin, labor in certain circumstances when the mother's labor has not started naturally.
These circumstances may include:
the mother's being past her due date; that is, the pregnancy has lasted longer than 40 weeks.
Labor is especially likely to be induced if tests indicate a decrease in the volume of amniotic fluid.
Uterotonics may also be used in cases of premature rupture of the membranes; preeclampsia (elevated blood pressure in the later stages of pregnancy); diabetes; and intrauterine growth retardation (IUGR), if these conditions require delivery before labor has begun.
Uterine stimulants are also used in the augmentation of existing contractions, to increase their strength and frequency when labor is not progressing well.
Normal results of drugs stimulating labor
The normal results of uterine stimulants, when administered in appropriate circumstances and correct dosages, are :
preparation of the cervix for childbirth
induction or stimulation of uterine contractions to produce a safe delivery of a newborn.
Encouragement of a complete spontaneous or induced abortion;
Elimination of blood clots or other tissue debris from the uterus
Slowing or cessation of hemorrhage following childbirth or abortion.
Precautions
It is important to establish a clear baseline of vital signs before a woman is given any uterine stimulant.
A faster pulse and a drop in blood pressure signal a potential hemorrhage.
When oxytocin is given intravenously, it must be diluted in IV fluid and never given as a straight IV.
PGs should not be administered if there is any question about the condition of the fetus—for example, an abnormal fetal heart rate tracing.
methylergometrine should never be given intravenously, and never to a woman with hypertension (high blood pressure).
DRUGS:
1. Oxytocin
Oxytocin is the drug of choice for induction of labor
The production and secretion of natural oxytocin is stimulated by the pituitary gland.
It is also available in synthetic form under the trade names of Pitocin and Syntocinon.
Uses:
Oxytocin is a naturally occurring hormone used to induce labor.
Oxytocin may be used in the treatment of a miscarriage to assure that all the products of conception are expelled from the uterus.
If the fetus died but was not expelled, a prostaglandin (PGE 2 ) may be given to ripen the cervix to facilitate a dilatation and evacuation, or to encourage uterine contractions.
In a routine delivery, oxytocin may be given to the mother after the placenta has been delivered in order to help the uterus contract and minimize bleeding.
It is also used to treat uterine hemorrhage
SIDE EFFECTS:
Oxytocin can cause hyperstimulation of the uterus, which in turn can place the fetus at risk for asphyxia.
“Hyperstimulation is defined as more than five contractions in 10 minutes; contractions lasting longer than 60 seconds”.
Uterine rupture has also been linked to oxytocin administration, particularly when the drug is given for four hours or longer.
3. Oxytocin has a mild antidiuretic effect that is usually dose-related; it can lead to water intoxication (hyponatremia). Signs of water intoxication may include reduced urine output, confusion, nausea, convulsions, and coma.
4. Expectant mothers receiving oxytocin should have their blood pressure monitored closely, as both hypotension and hypertension can occur.
5. Other side effects of oxytocin include nausea, vomiting, cardiac arrhythmias, and fetal bradycardia (slowing of the heartbeat).
(When used judiciously, oxytocin is a very effective medication for the progression of labor. )
2. Prostaglandins
Prostaglandins (PGs) play a major role in stimulating the uterine contractions at the beginning of labor.
PGs may be used to ripen the cervix prior to induction.
Administration of prostaglandins is sometimes sufficient to stimulate labor, and the woman needs no further medication for labor to progress.
There are many PGs used in medicine, but the most significant are PGE 1 , PGE 2 , and PGF2 alpha .
SIDE EFFECTS:
PGs have significant systemic side effects. These include headache, nausea, diarrhea, tachycardia , vomiting, chills, fever, sweating, hypertension, and hypotension .
an increased risk of uterine hyperstimulation and uterine rupture.
PGF2 alpha can cause hypotension, pulmonary edema, and intense bronchospasms in women with asthma.
When used for abortion, it may result in sufficient blood loss to cause anemia, which may make a transfusion necessary.
3. Ergot alkaloids
Ergot alkaloids are derived from a fungus, Claviceps purpurea , which grows primarily on rye grain.
Drugs:
Ergometrine
methylergometrine
Indication:
Ergometrine produces sustained contractions of the uterus.
It has a medical use in obstetrics to facilitate delivery of the placenta and to prevent bleeding after childbirth by causing smooth muscle tissue in the blood vessel walls to narrow, thereby reducing blood flow.
It is usually combined with oxytocin (Syntocinon) as syntometrine.
Ergometrine Injection may be given by intramuscular or intravenous
Injection.
SIDE EFFECTS:
These drugs can cause hypertension, cardiovascular changes, cyanosis, muscle pain, tingling, other symptoms associated with decreased blood circulation, and severe uterine cramping.
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