Uterine stimulants

Definition

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.

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. 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.

Precautions

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).

Description

Oxytocin

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 (PGE2) 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 PGF2alpha (Hemabate), misoprostol (Cytotec), or the ergot alkaloid methylergonovine (Methergine).

Prostaglandins

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 PGE1, PGE2, and PGF2alpha. Researchers are investigating which prostaglandins are the most effective for specific purposes. For example, PGE2 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 PGE1, is also effective in cervical ripening and labor induction, while the PGF2alpha analogue, carboprost (Prostin 15-M, or Hemabate), is the preferred prostaglandin for stimulating the uterus.

Ergot alkaloids

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.

Preparation

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.

Aftercare

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.

Risks

Oxytocin

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.

Prostaglandins

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. PGF2alpha (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

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.

Normal results

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.

Resources

books

Creasy, Robert K., and Robert Resnik. Maternal-Fetal Medicine, 4th ed. Philadelphia, PA: W. B. Saunders Company, 1999.

Rakel, Robert A., MD, ed. Conn's Current Therapy 2000. Philadelphia, PA: W. B. Saunders Company, 2000.

Scott, James. Danforth's Obstetrics and Gynecology, 8th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 1999.

Wilson, Billie Ann, RN, PhD, Carolyn L. Stang, PharmD, and Margaret T. Shannon, RN, PhD. Nurses Drug Guide 2000. Stamford, CT: Appleton and Lange, 1999.

organizations

American College of Obstetricians and Gynecologists (ACOG). 409 12th St. SW, PO Box 96920, Washington, DC 20090-6920. <www.acog.com>.

United States Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857-0001. (888) INFO-FDA. <www.fda.gov>.

Esther Csapo Rastegari, R.N., B.S.N., Ed.M. Sam Uretsky, PharmD

uterus The uterus has three major functions: to prepare a bed for a fertilized ovum, to nourish the developing embryo during pregnancy, and to expel the fetus. Shaped like an upside-down pear, and tilted forwards, it lies within the pelvis and is held in place, along with its two extensions, the Fallopian tubes, by ligaments and folds of the peritoneum. The cervix forms the lower third, connected by a narrow isthmus to the main muscular body of the uterus. The non-pregnant uterus weighs 45–60 g and is 7–8 cm long but its weight increases more than ten-fold by the end of pregnancy.

The main bulk of the uterus is made up of smooth muscle fibres known as the myometrium. The inner layer of muscle fibres is arranged in a circular pattern and the outer layer in a longitudinal pattern with a middle layer of interlacing oblique fibres. Inside the muscle is a cellular lining with a glandular (secretory) surface — the endometrium. While the myometrium is responsible for contractions of the uterus (obviously particularly important during labour), it is the endometrium which develops in every cycle to prepare for an embryo, and which is shed during menstruation. Thus during reproductive years the uterus is a highly dynamic organ, its functions being controlled by oestrogen and progesterone secreted by the ovaries and by other hormones associated with pregnancy and labour.

At the time of puberty, when oestrogen secretion from the ovaries begins to rise, there is an increase in both the size of the uterus and the blood flow which it receives. When menstrual cycles are established both the myometrium and the endometrium show cyclical, hormone-dependent changes in structure and function. These change again after implantation of an embryo, during pregnancy, and at delivery.

In the first half of the menstrual cycle the uterus prepares to receive and transport sperm from the cervix to the oviducts (Fallopian tubes). Under the influence of oestrogen secreted by the ovaries, the myometrium becomes more excitable and begins to contract sporadically. Meanwhile the cells under the surface of the endometrium begin to proliferate (hence the term proliferative phase of the uterine cycle) and those on the surface grow projections into the cavity of the uterus and invade the deeper layer underneath. Thus, from a relatively smooth surface at the beginning of each cycle, the endometrium not only thickens but becomes a highly indented structure, with the epithelial glands secreting a watery fluid. Spiral arteries grow up into the projections.

Towards mid-cycle, as ovulation approaches, the uterus is primed to bind progesterone. Thus, in the second half of the menstrual cycle, when progesterone production by the ovaries is high, the progestogenic or secretory phase of the uterine cycle begins. Progesterone stimulates the glandular cells of the lining to produce a thick secretion rich in proteins, sugars, and amino acids, and the whole endometrium thickens. The spiral arteries become fully developed and show rhythmic dilatations and constrictions. Progesterone also causes an increase in the size of the smooth muscle cells of the myometrium, but, in contrast to oestrogen, progesterone reduces excitability and so contractions are quietened. So the uterus prepares itself for an embryo, with an endometrium about 5 mm thick and well supplied with blood. It is important to note that these actions of progesterone will only occur if the uterus has been primed with oestrogen during the first half of the cycle.

If fertilization does not occur, the corpus luteum begins to degenerate and its hormone secretions begin to wane. The uterus loses its hormonal support, blood flow to the endometrial tissue is reduced, and consequently this lining layer dies. However, there is some bleeding from the spiral arteries into the disintegrating endometrium, and thus blood and dead cells are shed through the cervix and vagina. At the end of menstruation the endometrium is only about 0.5 mm thick — the change in thickness has been ten-fold.

The cervix also shows cyclical changes with each menstrual cycle. In the first half of the cycle, under the influence of oestrogen, the tissue becomes more vascular, the muscle relaxes and the lining becomes more secretory. In the second half of the cycle when progesterone production is elevated secretion is reduced and the tissue becomes firmer. However, the most important changes seen in the cervix are in the composition and properties of mucus secreted by its lining. Tests on cervical mucus are important since a hostile, impenetrable mucus can reduce fertility. As ovulation approaches the water and salt content of the mucus increase and it becomes less viscous, allowing for easier penetration of sperm. If mucus is taken from a cervical smear at this stage of the cycle and allowed to dry on a glass slide, a characteristic fern-leaf pattern of crystallization occurs, known as ferning. One can also draw this mucus out into long threads — a property known as spinnbarkheit. In contrast, mucus obtained in the second half of the cycle is thick, and strands of mucus cannot be stretched far before they break — a low spinnbarkheit. Thus the ability of sperm to penetrate cervical mucus is high at ovulation but low during the luteal phase when progesterone secretion is elevated. Indeed, the effects of progesterone on cervical mucus are such that low-dose progestogenic contraceptives given throughout the cycle can suppress sperm penetration through the cervix even at the time of ovulation when oestrogen levels are high.

In pregnancy the increase in size of the uterus is impressive: its walls remain thick despite the distension, because of the dramatic growth of its muscle fibres. The size and number of the blood vessels which supply it increase, carrying a twenty-fold increase in blood flow by full term. After delivery it shrinks rapidly, although taking some weeks to return to its previous size.

Saffron Whitehead

uterus in most female mammals, hollow muscular organ in which the fetus develops and from which it is delivered at the end of pregnancy . The human uterus is pear-shaped and about 3 in. (7.6 cm) long (it expands greatly during pregnancy); it normally lies in the pelvis, where it is supported by a ligament on either side extending to the pelvic wall. The body of the uterus tapers down to a necklike structure (cervix) that leads into the vagina. On either side of the uterus is an oviduct (called fallopian tube, or uterine tube, in humans) from 3 to 5 in. (7.6–12.7 cm) long, one end opening into the uterus and the other, wide-mouthed, ends in close proximity to an ovary . These oviducts serve as passageways for the ova to reach the uterus. Fertilization occurs in the oviduct; the fertilized ovum then continues into the uterus, where it becomes implanted in the lining of that organ, also known as the endometrium. If fertilization does not occur, the ovum and the lining of the uterine wall pass out of the body through the vagina (see menstruation ). Endometrial tissues then build up again in the uterus in anticipation of the next release of an ovum.

Diseases that can affect the uterus include various sexually transmitted diseases , pelvic inflammatory disease , and endometriosis , as well as benign or malignant tumors. Benign tumors may be removed without damage to the uterus, although in cases where the tissue is found to be cancerous, the entire uterus and cervix may have to be removed in a procedure known as hysterectomy . Prolapse of the uterus occurs when weakened supporting structures allow the uterus to tilt and slip downward into the vagina. See also reproductive system .

uterus (womb) (yoo-ter-ŭs) n. the part of the female reproductive tract that is specialized to allow the embryo to become implanted in its inner wall and to nourish the growing fetus from the maternal blood. The nonpregnant uterus is a pear-shaped organ, about 7.5 cm long, suspended in the pelvic cavity. The upper two thirds (body) is connected to the two Fallopian tubes and the narrower lower third (cervix) projects at its lower end into the vagina. u. didelphys double uterus: a congenital condition resulting from incomplete midline fusion of the two Müllerian ducts during early embryonic development. The usual result is a double uterus with one or two cervices and a single vagina. Complete failure of fusion results in a double uterus with double cervices and two separate vaginae.

uterus (womb) The organ of female mammals in which the embryo develops. Paired in most mammals but single in humans, it is situated between the bladder and rectum and is connected to the fallopian tubes and to the vagina. The lining (see endometrium) shows cyclical changes (see menstrual cycle; oestrous cycle) associated with egg production and provides a thick spongy layer in which the fertilized egg becomes embedded. The outer wall of the uterus (myometrium) is thick and muscular; by contracting, it forces the fully grown fetus through the vagina to the outside.

uterus In female mammals (except Monotremata), the organ in which the embryo develops. It is paired in most species but single in Primates, and is connected with Fallopian tubes and to the exterior by the vagina. The uterus undergoes changes during the oestrus (or menstrual cycle), and in oestrous its glandular lining provides a spongy layer in which a fertilized egg may be implanted. The outer walls of the uterus are thick and muscular, their contractions during birth forcing the foetus through the vagina.

uterus (womb) Hollow muscular organ located in the pelvis of female mammals. It protects and nourishes the growing fetus until birth. The upper part is broad and branches out on each side into the Fallopian tubes. The lower uterus narrows into the cervix, which leads to the vagina. Its muscular walls are lined with endometrium (mucous membrane), to which the fertilized egg attaches itself. See also menstrual cycle

u·ter·us / ˈyoōtərəs/ • n. (pl. u·ter·i / ˈyoōtəˌrī; -ˌrē/ ) the organ in the lower body of a woman or female mammal where offspring are conceived and in which they gestate before birth; the womb.

uterus (anat.) womb. XVII. — L. uterus belly, womb, obscurely rel. to Skr. udára-, Gr. hóderos.
So uterine having the same mother XV; pert. to the uterus XVII. — late L. uterīnus.

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