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 (start) 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 the oxytocins, prostaglandins, and ergot alkaloids. Uterotonics may be given intravenously (IV), intramuscularly (IM), as a vaginal gel or suppository, or by mouth.
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. These medications may be recommended if the expectant mother lives a great distance from the healthcare facility and there is concern for either her or her baby's safety if she were unable to reach the facility once labor begins.
Uterine stimulants are also used in the augmentation of existing contractions, to increase their strength and frequency when labor is not progressing well.
According to the American College of Obstetrics and Gynecology (ACOG), the 1990s saw an increase in the rate of induced labor—from 9% of deliveries to 18%. The ACOG reported in May 2001 that the increase in the rate of Caesarian sections seen over the same period of time was not due to the induction process but to such other factors as the condition of the mother's cervix at the time of induction and whether the pregnancy was the woman's first.
It is important to establish a clear baseline of vital signs before a woman is given any uterine stimulant. Consistent reevaluation and documentation of vital signs permit faster recognition of an abnormal change in a woman's condition. Documentation includes the time and dosage of any medications given, as well as a record of any side effects. 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. Methergine should never be given intravenously, and never to a woman with hypertension (high blood pressure).
Oxytocin is a naturally occurring hormone used to induce 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.
Oxytocin is used in a contraction stress test (CST). A CST is done prior to the onset of labor to evaluate the fetus's ability to withstand the contractions of the uterus. To avoid the possibility of exogenous (introduced) oxytocin putting the woman into labor, she may instead be asked to stimulate her nipples to release her natural oxytocin. A negative, or normal, CST result is three contractions within a 10-minute period with no abnormal slowing of the fetal heart rate (FHR). The CST occasionally produces false positives, however.
Oxytocin may be used in the treatment of a miscarriage to assure that all the products of conception (POC) 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. The prostaglandin may be administered either in gel form or as a vaginal suppository.
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. While hemorrhage occurs in about 4% of vaginal deliveries and 6% of Caesarian deliveries, it accounts for about 35% of maternal deaths due to bleeding during pregnancy. If the bleeding started at the placental detachment site, contractions of the uterus help to close off the blood vessels and thereby stop excessive bleeding. Additional medications may be used, including PGF2 alpha (Hemabate), misoprostol (Cytotec), or the ergot alkaloid methylergonovine (Methergine).
Prostaglandins (PGs) play a major role in stimulating the uterine contractions at the beginning of labor. Research indicates that PGs are also involved in the transition from the early phase of labor to the later stages. In addition, 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 . Researchers are investigating which prostaglandins are the most effective for specific purposes. For example, PGE 2 in the form of dinoprostone (Cervidil and Prepidil) has proved to be superior to the PGF series for cervical ripening. Misoprostol (Cytotec), a synthetic form of PGE 1 , is also effective in cervical ripening and labor induction, while the PGF2 alpha analogue, carboprost (Prostin 15-M, or Hemabate), is the preferred prostaglandin for stimulating the uterus.
Ergot alkaloids are derived from a fungus, Claviceps purpurea , which grows primarily on rye grain. The fungus forms a hard blackish body known as a sclerotium, which contains alkaloid compounds that can be used to treat migraine headache. Ergot by itself, however, is toxic to the central nervous system of humans and animals, producing irritability, spasms, cramps, and convulsions. Because of its potentially harmful side effects, one ergot-based drug (Ergonovine or Ergotrate) was taken off the American market in 1993. Methylergonovine maleate (Methergine) is now the only ergot derivative in use in the United States. It is given only as a uterine stimulant to control PPH. Because of the risk of complications, and because the use of Methergine is contraindicated in many women, it has largely been replaced by the PGs as a second-line uterotonic.
A health care professional should review information about a medication or procedure with the pregnant woman before administering it to make sure that she understands what will happen during the procedure or the potential side effects of the medication. The patient should inform the doctor or nurse about any allergies to medications, as well as any side effects she may have experienced previously.
If the patient is anxious about induction of labor or augmentation of contractions, the nurse or doctor should discuss these concerns and relieve the patient's anxiety.
The expectant mother should be monitored closely during induction of labor or cervical ripening. The FHR and uterine contractions are usually monitored for an hour after induction. Frequent checks of the patient's vital signs alert the nurse to any potential complications.
Oxytocin takes effect rapidly when it is given intravenously. Individual responses to oxytocin vary considerably; for this reason, the drug dosage is usually increased slowly and incrementally. 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, and increased uterine tonus either with or without significant decrease in FHR. Uterine rupture has also been linked to oxytocin administration, particularly when the drug is given for four hours or longer.
Oxytocin has a mild antidiuretic effect that is usually dose-related; it can lead to water intoxication (hyponatremia). Onset occurs gradually and may go unnoticed. Signs of water intoxication may include reduced urine output, confusion, nausea, convulsions, and coma. Expectant mothers receiving oxytocin should have their blood pressure monitored closely, as both hypotension and hypertension can occur.
Although the subject remains controversial, some evidence suggests oxytocin increases the incidence of neonatal jaundice. Although oxytocin may increase the risk of uterine rupture in women who were delivered by Caesarian section in a previous pregnancy, contraindications to the use of the drug are virtually the same as contraindications for labor. 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.
PGs have significant systemic side effects. These include headache, nausea, diarrhea, tachycardia (rapid heartbeat), vomiting, chills, fever, sweating, hypertension, and hypotension (low blood pressure). There is also an increased risk of uterine hyperstimulation and uterine rupture. PGF2 alpha (carboprost—Prostin 15-M or Hemabate) can cause hypotension, pulmonary edema, and intense bronchospasms in women with asthma. Because carboprost stimulates the production of steroids, it may be contraindicated in women with disorders of the adrenal gland. When used for abortion, it may result in sufficient blood loss to cause anemia, which may make a transfusion necessary. Medical problems (or a history) of diabetes, epilepsy, heart or blood vessel disease, jaundice, kidney disease, or liver disease should be brought to the attention of the health care practitioner before the patient is given carboprost. The use of this PG has been reported to increase the fluid pressure in the eyes in women with glaucoma; however, this side effect is fortunately rare.
Ergot alkaloids have an alpha-adrenergic action with a vasoconstrictive effect, which means that they cause the blood vessels to become narrower. These drugs can cause hypertension, cardiovascular changes, cyanosis, muscle pain, tingling, other symptoms associated with decreased blood circulation, and severe uterine cramping. The health care professional should be informed of other medications taken by the patient. The presence or history of such medical problems as angina, hypertension, stroke, infection, kidney and liver disease, and Raynaud's phenomenon may be contraindications to the use of ergot alkaloids.
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; and the slowing or cessation of hemorrhage following childbirth or abortion.
Normal results would include the achievement of these outcomes without significant side effects for the mother or fetus.
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American College of Obstetricians and Gynecologists (ACOG). 409 12th St. SW, PO Box 96920, Washington, DC 20090-6920. http://www.acog.com .
United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. (888) INFO-FDA. http://www.fda.gov .
Esther Csapo Rastegari, R.N., B.S.N., Ed.M. Sam Uretsky, PharmD