Tutoring at home http://tutoring123.net Sat, 24 Sep 2011 10:06:16 +0000 en hourly 1 http://wordpress.org/?v=3.1.1 Normal Labor and Deliver http://tutoring123.net/normal-labor-and-deliver.htm http://tutoring123.net/normal-labor-and-deliver.htm#comments Sat, 24 Sep 2011 10:06:16 +0000 admin http://tutoring123.net/?p=388 Childbirth is the period from the onset of regular uterine contractions until expulsion of the placenta. The process by which this normally occurs is called labor—a term that in the obstetrical context takes on several connotations from the English language. According to the New Shorter Oxford English Dictionary (1993), toil, trouble, suffering, bodily exertion, especially when painful, and an outcome of work are all characteristics of labor and thus implicated in the process of childbirth. Such connotations all seem appropriate to us and emphasize the need for all attendants to be supportive of the laboring woman’s needs, particularly in regard to effective pain relief.
At Parkland Hospital in 2003, only 53 percent of 12,139 women with singleton cephalic presentations at term had a spontaneous labor and delivery. The remainder had ineffective labor requiring augmentation (29 percent) or other medical and obstetrical complications requiring induction of labor. It seems excessive to consider almost 50 percent of parturients as “abnormal” because they did not spontaneously labor and deliver. Hence, the distinction between normal and abnormal is often subjective. This high prevalence of labor abnormalities, however, can be used to underscore the importance of labor events in the successful outcome of pregnancy.

]]> http://tutoring123.net/normal-labor-and-deliver.htm/feed 0 Preconceptional Counselors http://tutoring123.net/preconceptional-counselors.htm http://tutoring123.net/preconceptional-counselors.htm#comments Sat, 24 Sep 2011 07:15:29 +0000 admin http://tutoring123.net/?p=385 Practitioners providing routine health maintenance for reproductive-aged women have the best opportunity to provide preventive counseling. Gynecologists, internists, family practitioners, and pediatricians can do so at the annual examination. The occasion of a negative pregnancy test is a good time for counseling. Jack and associates (1995) administered a comprehensive preconceptional risk survey to 136 women who had a negative pregnancy test in an ambulatory general practice clinic. Almost 95 percent of these women reported at least one problem that could affect a future pregnancy. These included medical or reproductive problems (52 percent), a family history of genetic diseases (50 percent), increased risk of contracting HIV (30 percent), increased risk of contracting hepatitis B and use of illegal substances (25 percent), alcohol use (17 percent), and nutritional risk (54 percent).
Basic preconceptional advice regarding diet, alcohol use, smoking, illicit drug use, vitamin intake, exercise, and other behaviors can be provided by the primary care provider, including the obstetrician-gynecologist. Medical records should be obtained and reviewed. Counselors should be knowledgeable about relevant medical diseases, prior surgery, reproductive disorders, or genetic conditions, and must be able to interpret data and recommendations provided by other specialists. The practitioner who is uncomfortable providing counseling should refer the woman or couple to a counselor with special expertise.

]]> http://tutoring123.net/preconceptional-counselors.htm/feed 0 Genetic Diseases http://tutoring123.net/genetic-diseases.htm http://tutoring123.net/genetic-diseases.htm#comments Sat, 24 Sep 2011 07:14:35 +0000 admin http://tutoring123.net/?p=383 Birth defects are currently the leading cause of infant mortality and account for 20 percent of all infant deaths. These defects can be avoided with three types of prevention strategies. The preferred strategy is primary prevention—avoidance of causal factors—which is becoming possible for more congenital diseases as their etiologies are discovered. Secondary prevention—identifying and terminating affected pregnancies—is an alternative strategy for single-gene disorders and other defects that cannot be prevented. Surgical correction of structural defects is one type of tertiary prevention, but it is not possible for most genetic disorders. The benefits of preconceptional counseling usually are measured by comparing the incidence of new cases before and after the initiation of a counseling program. Some examples of congenital conditions that clearly benefit from counseling include neural-tube defects, phenylketonuria, Tay-Sachs disease, and the thalassemias.
Neural-Tube Defects (NTDs)
The incidence of these defects is 1 to 2 per 1000 live births, and they are second only to cardiac anomalies as the most frequent structural fetal malformation. Some NTDs are associated with a specific mutation in the methylene tetrahydrofolate reductase gene (677C T), the adverse effects of which appear to be largely overcome by periconceptional folic acid supplementation (Ou and associates, 1996; van der Put and colleagues, 1995). The Medical Research Council on Vitamin Study Research Group (1991) conducted a randomized double-blind study of preconceptional folic acid therapy at 33 centers in seven European countries. Women with a previous affected child who took supplemental folic acid before conception and throughout the first trimester reduced their NTD recurrence risk by 72 percent. Perhaps more importantly, because 90 to 95 percent of NTDs occur in families with no prior history, Czeizel and Dudas (1992) subsequently showed that supplementation reduced the a priori risk of a first NTD occurrence.
Phenylketonuria (PKU)
This disorder is an inborn error of phenylalanine metabolism. It is an example of a disease in which the fetus is not at risk to inherit the disease but may be damaged by the effects of maternal genetic disease. For such conditions, preconceptional counseling regarding strategies to improve the intrauterine environment constitutes primary prevention and may significantly reduce fetal morbidity. Individuals with PKU who eat an unrestricted diet have abnormally high blood phenylalanine levels. This amino acid readily crosses the placenta and can damage developing fetal organs, especially neural and cardiac tissues. With preconceptional counseling and adherence to a phenylalanine-restricted diet before pregnancy, the incidence of fetal malformations is dramatically reduced (Guttler and colleagues, 1990; Koch and associates, 1990).
The Maternal Phenylketonuria Collaborative Study evaluated the effectiveness of preconceptional care in preventing PKU-related fetal defects (Rouse and co-workers, 1997). Almost 300 women with PKU began a low-phenylalanine diet before pregnancy. Compared with infants whose mothers had poor dietary control, infants of women achieving good control had a lower incidence of microcephaly (6 versus 15 percent), neurological abnormalities (4 versus 14 percent), and cardiac defects (none versus 16 percent). The proportion of women treated preconceptionally increased from 7 to 51 percent from 1984 to 1994 (Platt and colleagues, 2000).
Tay-Sachs Disease
This disease is a severe, autosomal-recessive neurodegenerative disorder that leads to death in childhood. The effectiveness of preconceptional counseling in reducing genetic disease has been most clearly demonstrated in Tay-Sachs disease. In the early 1970s, there were approximately 60 new cases in the United States each year, primarily in individuals of Jewish heritage. An intensive worldwide campaign was initiated to counsel Jewish men and women of reproductive age, to identify carriers through genetic testing, to provide prenatal testing—secondary prevention—for high-risk couples, and even to help heterozygote carriers choose unaffected mates—primary prevention! The outcome of this initiative has been monitored by the National Tay-Sachs Disease and Allied Disorders Association (Kaback and colleagues, 1993). Within 8 years of its inception, nearly 1 million young adults around the world had been tested and counseled, and the incidence of new Tay-Sachs cases has plummeted to only about five new cases per year. Currently, most new cases are in the non-Jewish population.
Thalassemias
These disorders of globin-chain synthesis are the most common single-gene disorders worldwide. Approximately 200 million people carry a gene for one of these hemoglobinopathies (Benz, 2001). Hundreds of mutations have been identified that cause several important thalassemia syndromes. Some of these could be avoided by both primary and secondary prevention (Fucharoen and associates, 1991; Wong, 1985). In endemic areas such as Mediterranean countries, counseling and other prevention strategies have reduced the incidence of new cases by at least 80 percent (Angastiniotis and Modell, 1998). Experiences with a long-standing counseling program aimed at Montreal high school students at risk were summarized by Mitchell and colleagues (1996). Over a 20-year period, 25,274 students of Mediterranean origin were counseled and tested for -thalassemia. Within a few years of initiating the preconceptional program, all high-risk couples who requested prenatal diagnosis had already been counseled, and no affected children have been born since that time.

]]> http://tutoring123.net/genetic-diseases.htm/feed 0 Chronic Medical Disorders http://tutoring123.net/chronic-medical-disorders.htm http://tutoring123.net/chronic-medical-disorders.htm#comments Sat, 24 Sep 2011 07:12:38 +0000 admin http://tutoring123.net/?p=381 Diabetes Mellitus
Because maternal and fetal pathology associated with hyperglycemia is well known, diabetes is the prototype of a condition for which preconceptional counseling is beneficial. Many of these complications can be avoided if conception occurs when glucose control is optimal (Jovanovic and colleagues, 1981). Such control requires either that glucose levels be chronically well regulated—always a goal, but difficult to achieve—or that the woman make necessary changes before attempting conception. Preconceptional counseling can educate her about risks and provide a program designed to reduce them (Bernasko, 2004).
The utility of preconceptional counseling in preventing diabetes-related complications at all stages of pregnancy has been confirmed. Importantly, all studies showed that counseling is associated with significantly fewer malformations.
Dunne and co-workers (1999) reviewed the impact of preconceptional counseling on other diabetes-related neonatal morbidity. Women who received counseling sought prenatal care earlier, had lower hemoglobin A1c levels, and were less likely to smoke during pregnancy. Their outcomes were compared with those of a cohort of women who did not receive such counseling. Of the women who received counseling, none were delivered before 30 weeks compared with 17 percent in the uncounseled group. In addition, the counseled women had fewer macrosomic infants—25 versus 40 percent; they had no growth-restricted infants compared with 8.5 percent; they had no neonatal deaths compared with 6 percent; and their infants had 50 percent fewer admissions to the intensive care nursery—17 versus 34 percent.
Preconceptional counseling also reduces obstetrical complications and health care costs in diabetic women. In a prospective multicenter observational trial from five Michigan centers, Herman and colleagues (1999) confirmed these benefits. They reported that diabetic women who received preconceptional counseling reported for prenatal care 3 weeks earlier than uncounseled women; they had lower hemoglobin A1c levels; they were significantly less likely to require antepartum hospitalization for diabetes control—8 versus 68 percent; and they had significantly fewer hospitalization days—4.5 versus 15.7. Counseled women also had fewer episodes of hypoglycemia and diabetic ketoacidosis; they had no hypertensive complications; and their postpartum stay was 2 days shorter than that of uncounseled women. These improved outcomes were associated with savings of $34,000 in direct medical costs per patient who received counseling.
Epilepsy
Women with epilepsy are two to three times more likely to have infants with structural anomalies than unaffected women (Chang and McAuley, 1998; Wide and associates, 2004). Some reports indicate that epilepsy itself increases the incidence of congenital anomalies, independent of the effects of antiseizure medication. In a recent study, however, Holmes and colleagues (2001) compared 509 epileptic women who took antiseizure medication during pregnancy to 606 who did not. They found that only infants exposed to anticonvulsant medications had an increased incidence of structural anomalies. Fetuses exposed to one drug had significantly fewer malformations than those exposed to two or more drugs—21 versus 28 percent. By contrast, the incidence of defects in fetuses of epileptic mothers who did not take medication was only 8.5 percent—the same as in fetuses of women without seizure disorders. Preconceptional counseling usually includes recommendations to switch to monotherapy with the least teratogenic medication (Adab and colleagues, 2004; American Academy of Neurology, 1998). The risks of antiseizure medication are described in detail in Chapter 14 (see Anticonvulsant Medications).
Epileptic women also are advised to take supplemental folic acid. Biale and Lewenthal (1984) performed a retrospective case-control study to evaluate effects of periconceptional folate supplementation in women taking anticonvulsants. Although 10 of 66 (15 percent) unsupplemented pregnancies resulted in offspring with congenital malformations, none of 33 neonates of supplemented women had anomalies. Depending on the history, a trial period without anticonvulsants also may be recommended.
Other Chronic Diseases
Cox and co-workers (1992) reviewed pregnancy outcomes of 1075 high-risk women who received preconceptional counseling. If they received counseling, 240 women with hypertension, renal disease, thyroid disease, asthma, and heart disease had significantly better outcomes than previous pregnancies. Indeed, 80 percent of those counseled gave birth to a normal infant compared with only 40 percent in the previous uncounseled gestation.

]]> http://tutoring123.net/chronic-medical-disorders.htm/feed 0 Unplanned Pregnancy http://tutoring123.net/unplanned-pregnancy.htm http://tutoring123.net/unplanned-pregnancy.htm#comments Sat, 24 Sep 2011 07:09:05 +0000 admin http://tutoring123.net/?p=379 To be effective, counseling about potential pregnancy risks and strategies to prevent them must be provided before conception. By the time most women realize they are pregnant—1 to 2 weeks after the first missed period—the fetal spinal cord has already formed and the heart is beating (Moore, 1983). Many prevention strategies, for example, folic acid to prevent neural-tube defects, are ineffective if initiated at this time. The Centers for Disease Control and Prevention (1999) estimate that up to half of all pregnancies are unplanned, and there is evidence that these may be at greatest risk.
Adams and colleagues (1993) conducted a population-based survey of almost 12,500 women in four states and found that women with unintended pregnancies were more likely than those with planned pregnancies to have an indication for preconceptional counseling. Hellerstedt and co-workers (1998) surveyed nearly 7200 pregnant women and found that women with unintended pregnancies were more likely to have high-risk behaviors. Jack and associates (1995) administered a comprehensive risk survey to 136 women at the time of a negative pregnancy test. They found that (1) the majority did not want to be pregnant, (2) half reported a medical or reproductive risk that could adversely affect pregnancy, (3) half reported a genetic risk, and (4) one fourth reported risks for human immunodeficiency virus (HIV) and hepatitis B infection or alcohol or recreational drug use. Unwanted pregnancies are particularly common in the unmarriedurban poor (Besculides and Laraque, 2004).
An important measure of the effectiveness of preconceptional counseling is, therefore, its influence in reducing the number of unintended pregnancies. Moos and colleagues (1996) instituted a preconceptional care program for reproductive-aged women who visited a health department clinic and then also studied 1378 women who sought prenatal care. They reported that the 456 women who had preconceptional counseling had a 50-percent greater likelihood of describing their pregnancies as intended compared with that of 309 women with health care but no counseling, and a 65-percent greater likelihood compared with that ofwomen with no health care prior to pregnancy.

]]> http://tutoring123.net/unplanned-pregnancy.htm/feed 0 Preconceptional Counseling http://tutoring123.net/preconceptional-counseling.htm http://tutoring123.net/preconceptional-counseling.htm#comments Sat, 24 Sep 2011 07:08:03 +0000 admin http://tutoring123.net/?p=377 In the early part of the 20th century, women with medical problems were often unable to conceive or were advised not to. Discoveries such as insulin and the development of effective antihypertensive medications subsequently made it possible for many of these women to contemplate pregnancy. Obstetrical care of women with medical problems during this time dealt almost exclusively with protecting maternal health, as little was known about pathological influences on fetal development. In the 1960s, research began to focus on the pathophysiology of pregnancy and perinatal outcome. As a result, prenatal care was gradually extended to include fetal concerns, and interest in perinatal research increased dramatically. The etiologies of many maternal and fetal conditions were determined, and research also clarified the genetic origins of many diseases. At the same time, effective contraception was developed, allowing women to postpone pregnancy and limit family size while striving to optimize perinatal outcome. The focus of obstetrical care thus changed once again, from treating maternal and fetal diseases to predicting and preventing them.
In 2000, the Public Health Service released Healthy People 2010, a guide for the second nationwide preventive medicine program. The major goals are to increase the quality and years of healthy life and to eliminate health disparities between individuals. More specifically, it strives to improve the health and well-being of women, infants, children, and families.
Preconceptional counseling can play a major role in achieving these goals. As stated in the Department of Health and Human Services report on the program: “Preconceptional screening and counseling offer an opportunity to identify and mitigate maternal risk factors before pregnancy begins.” For example, the two leading causes of death in the first year of life—birth defects and disorders caused by preterm birth—can both be significantly reduced or eliminated by the preconceptional initiation of specific preventive strategies. Morbidity caused by a variety of factors, including uncontrolled maternal disease, environmental exposures, and nutritional deficiencies, also can be prevented by preconceptional care. Furthermore the intrauterine fetal environment has a tremendous impact on the health and well-being of the adult that fetus will become—the Barker hypothesis (Barker, 1994). Thus, optimizing pregnancy conditions and outcomes has long-term health impacts that are only beginning to be apparent. The 1989 Public Health Service Expert Panel on the Content of Prenatal Care rightfully concluded: “The preconceptional visit may be the single most important health care visit when viewed in the context of its effect on pregnancy.”

]]> http://tutoring123.net/preconceptional-counseling.htm/feed 0 Cell Surface Receptors As Regulators of Myometrium http://tutoring123.net/cell-surface-receptors-as-regulators-of-myometrium.htm http://tutoring123.net/cell-surface-receptors-as-regulators-of-myometrium.htm#comments Fri, 23 Sep 2011 01:00:55 +0000 admin http://tutoring123.net/?p=373 Myometrial cells have developed a unique system of regulatory pathways that rely not only on estrogen and progesterone receptors but also on a variety of cell surface receptors that can directly regulate the contractile state of the cell. The three major classes of cell surface receptors are the G-protein–linked, ion channel–linked, and enzyme-linked. Multiple examples of each class of receptors have been identified in human myometrium, and examples of each class appear to be modified during the phases of parturition. Most of these heptahelical receptors are associated with the activation of adenylyl cyclase. Other heptahelical receptors in myometrium, however, are more commonly associated with G-protein–mediated activation of phospholipase C, which will lead to increased [Ca2+]i and myometrial cell contraction. Many G-protein–coupled receptors that participate in regulation of myometrial activity have been characterized. These were reviewed recently by Lopez (2003).
Ligands for the heptahelical receptors include neuropeptides, hormones, and autacoids. Many of these are available to the myometrium during pregnancy in high concentration by several routes: from maternal blood (endocrine), contiguous tissues or adjacent cells (paracrine), or direct synthesis in the myometrial smooth muscle cells (autocrine) (Fig. 6–16). It is important to note that the myometrial response to a hormone can change during the course of pregnancy. Thus, it is conceivable that hormone action on the myometrium is regulated at several levels, including the expression of the heptahelical receptor, its associated G-proteins, or the effector proteins in the plasma membrane. Specifically, the imposition of quiescence (activation of adenylyl cyclase) or the facilitation of contractions (activation of phospholipase C and increased [Ca2+]i) may in some cases be regulated by the same hormone.

]]> http://tutoring123.net/cell-surface-receptors-as-regulators-of-myometrium.htm/feed 0 Regulation of Myometrial Contraction and Relaxation http://tutoring123.net/regulation-of-myometrial-contraction-and-relaxation.htm http://tutoring123.net/regulation-of-myometrial-contraction-and-relaxation.htm#comments Fri, 23 Sep 2011 00:39:08 +0000 admin http://tutoring123.net/?p=369 The control of myometrial contraction is at the heart of understanding both the maintenance of pregnancy and the onset of labor. The regulation of myometrial cell contraction versus relaxation can be divided temporally into acute and chronic mechanisms. Acutely, the interaction of myosin and actin is essential to muscle contraction. Myosin (Mr about 500,000) is comprised of multiple light and heavy chains and is arranged in thick myofilaments. The interaction of myosin and actin, which causes activation of adenosine triphosphatase, adenosine triphosphate hydrolysis, and force generation, is effected by enzymatic phosphorylation of the 20-kd light chain of myosin (Stull and colleagues, 1988, 1998). This phosphorylation reaction is catalyzed by the enzyme myosin light chain kinase, which is activated by calcium. Calcium binds to calmodulin, a calcium-binding regulatory protein, which in turn binds to and activates myosin light chain kinase. In this manner, agents that act on myometrial smooth muscle cells to cause an increase in the intracellular cytosolic concentration of calcium ([Ca2+]i) promote contraction. The increase in [Ca2+]i is often transient, but contractions can be prolonged through the inhibition of myosin phosphatase activity by Rho kinase, which is activated in a receptor-dependent fashion (Woodcock and associates, 2004). Conditions that cause a decrease in [Ca2+]i favor relaxation. Ordinarily, agents that cause an increase in the intracellular concentration of cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP) promote uterine relaxation. It is believed that cAMP and cGMP act to cause a decrease in [Ca2+]i, although the exact mechanism(s) is not defined.

Myometrial cell contractions also can be greatly influenced by the chronic action of hormones on the contractile status of the cell. This influence can occur through the effects that mediate the transcription of key genes that repress or enhance the contractility of the cell. Considerable data indicate that uterine activity is influenced through the regulation of the so-called contraction-associated proteins (CAPs). These proteins include channels associated with smooth muscle excitation and contraction, gap junction components, and uterotonic stimulatory or inhibitory receptors.

]]> http://tutoring123.net/regulation-of-myometrial-contraction-and-relaxation.htm/feed 0 Physiological and Biochemical Processes Regulating Parturition http://tutoring123.net/physiological-and-biochemical-processes-regulating-parturition.htm http://tutoring123.net/physiological-and-biochemical-processes-regulating-parturition.htm#comments Fri, 23 Sep 2011 00:35:32 +0000 admin http://tutoring123.net/?p=367 The physiological processes in human pregnancy that result in the initiation of parturition and the onset of labor remain poorly defined. Presently, there are two general theorems on the mechanisms regulating the initiation of labor. Viewed simplistically, these are the retreat from pregnancy maintenance and the uterotonin induction of parturition hypotheses. Several combinations of selected tenets of these two postulates are incorporated into the theorems of most investigators.
Some researchers also speculate that the mature human fetus is the source of the initial signal for the commencement of the parturitional process. Other investigators suggest that one or more uterotonins, produced in increased amounts or an elevation in the population of its myometrial receptors, is the proximate cause of the initiation of human parturition. Indeed, an obligatory role for one or more uterotonins is included in most parturition theories, either as a primary or a secondary phenomenon in the final events of childbirth. Both of these suppositions rely on careful regulation of the activity of the myometrial smooth muscle cell contraction. Therefore, a detailed understanding of this critical tissue and its regulation aids in understanding normal and pathological progression of the various phases of parturition.

]]> http://tutoring123.net/physiological-and-biochemical-processes-regulating-parturition.htm/feed 0 Formation of Distinct Lower and Upper Uterine Segments http://tutoring123.net/formation-of-distinct-lower-and-upper-uterine-segments.htm http://tutoring123.net/formation-of-distinct-lower-and-upper-uterine-segments.htm#comments Fri, 23 Sep 2011 00:33:37 +0000 admin http://tutoring123.net/?p=364 During active labor, the divisions of the uterus that were initiated in phase 1 of parturition become increasingly evident. The actively contracting upper segment becomes thicker as labor advances. The lower or passive segment of the uterus and the cervix are relatively inactive compared with the upper segment. It subsequently develops into a much more thinly walled passage for the fetus. The lower segment is analogous to a greatly expanded and thinned-out isthmus in nonpregnant women and thus is not solely a phenomenon of labor. The lower segment develops gradually as pregnancy progresses and then thins remarkably during labor.
By abdominal palpation, even before rupture of the membranes, the two segments can be differentiated during a contraction. The upper uterine segment is quite firm or hard during contractions. The consistency of the lower uterine segment is much less firm, and it is distended and normally much more passive. If the entire wall of uterine musculature, including the lower uterine segment and cervix, were to contract simultaneously and with equal intensity, the net expulsive force would be decreased markedly. Herein lies the importance of the division of the uterus into an actively contracting upper segment and a more passive lower segment that differ not only anatomically but also physiologically.
The upper segment contracts, retracts, and expels the fetus. In response to the force of these contractions, the softened lower uterine segment and cervix dilate and thereby form a greatly expanded, thinned-out muscular and fibromuscular tube through which the fetus can be extruded. The myometrium of the upper uterine segment does not relax to its original length after contractions. Instead, it becomes relatively fixed at a shorter length.
The upper active segment of the uterus contracts down on its diminishing contents, but myometrial tension remains constant. The net effect is to take up slack, thus maintaining the advantage gained in the expulsion of the fetus, and keeping the uterine musculature in firm contact with the intrauterine contents. As the consequence of retraction, each successive contraction commences where its predecessor left off. Thus, the upper part of the uterine cavity becomes slightly smaller with each successive contraction. Because of the successive shortening of the muscular fibers with contractions, the upper active uterine segment becomes progressively thickened throughout the first and second stages of labor. This process continues and results in an upper uterine segment that is tremendously thickened immediately after delivery. The phenomenon of upper segment retraction is contingent upon a decrease in the volume of its contents. For the contents to be diminished, particularly early in labor when the entire uterus is virtually a closed sac with only a minute opening at the cervical os, the musculature of the lower segment must stretch. This permits increasingly more of the uterine contents to occupy the lower segment, and the upper segment retracts only to the extent that the lower segment distends and the cervix dilates.
Relaxation of the lower uterine segment is not complete, but rather the opposite of retraction. The fibers of the lower segment become stretched with each contraction of the upper segment and after which are not returned to the previous length but remain fixed at the longer length. Importantly, the tension remains essentially the same as before. The musculature still manifests tone, still resists stretch, and still contracts somewhat on stimulation. The successive lengthening of the fibers in the lower segment, as labor progresses, is accompanied by thinning, normally to only a few millimeters in the thinnest part. As a result of the lower segment thinning and concomitant upper segment thickening, a boundary between the two is marked by a ridge on the inner uterine surface—the physiological retraction ring. When the thinning of the lower uterine segment is extreme, as in obstructed labor, the ring is very prominent, forming a pathological retraction ring. This is an abnormal condition, also known as Bandl ring. The existence of a gradient of diminishing physiological activity from fundus to cervix was established from measurements of differences in behavior of the upper and lower parts of the uterus during normal labor.

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