Introduction and physiology of labor
- 8. • mini-labor • Parturient • Parturition Series of events that take place in the genital organs in an effort to expel the viable products of conception out of the womb through the vagina into the outer world is called Labor.
- 9. Delivery • Delivery is the expulsion or extraction of a viable fetus out of the womb. • It is not synonymous with labor; delivery can take place without labor as in elective cesarean section.
- 10. NORMAL LABOR (EUTOCIA) • Labor is called normal if it fulfils the following criteria. – (1) Spontaneous in onset and at term. – (2) With vertex presentation. –(3) Without undue prolongation. –(4) Natural termination with minimal aids. –(5) Without having any complications affecting the health of the mother and/or the baby.
- 11. ABNORMAL LABOR (DYSTOCIA): • Any deviation from normal labor is called Abnormal labor.
- 12. DATE OF ONSET OF LABOR: • It is very much unpredictable to foretell precisely the exact date of onset of labor. • It not only varies from case to case but even in different pregnancies of the same individual. • Calculation based on Naegele’s formula can only give a rough guide.
- 13. • Hippocrates concept that the fetus determines the time of its birth has been proven correct in animals. • In humans however ,it appears that the placenta and fetal membranes play major role in the initiation of labor ,while the fetus may modulate the timing of labor .
- 14. Causes of onset of labor • The precise mechanism of initiation of human labor is still obscure. • Endocrine, biochemical and mechanical stretch pathways as obtained from animal experiments, however, put forth the following hypotheses. Uterine distension Fetoplacental contribution Estrogen Progesterone Prostaglandins Oxytocin Neurological factors
- 15. Uterine distension • Stretching effect on the myometrium by the growing fetus and liquor amnii can explain the onset of labor at least in twins or polyhydramnios. • Uterine stretch increases gap junction proteins, receptors for oxytocin and specific contraction associated proteins (CAPS)
- 16. Fetoplacental contribution: • Cascade of events activate fetal hypothalamic pituitary adrenal axis prior to onset of labor → increased CRH • → increased release of ACTH • → fetal adrenals • → increased cortisol secretion • → accelerated production of estrogen and prostaglandins from the placenta
- 17. Placenta
- 18. Estrogen the probable mechanisms are: — Increases the release of oxytocin from maternal pituitary. — Promotes the synthesis of myometrial receptors for oxytocin (by 100– 200 folds), prostaglandins and increase in gap junctions in myometrial cells. — Accelerates lysosomal disintegration in the decidual and amnion cells resulting in increased prostaglandin (PGF) synthesis. — Stimulates the synthesis of myometrial contractile protein— actomyosin through cAMP. — Increases the excitability of the myometrial cell membranes.
- 19. Progesterone: • Increased fetal production of dehydroepiandrosterone sulfate (DHEA-S) and cortisol • Inhibits the conversion of fetal pregnenolone to progesterone. Progesterone levels therefore fall before labor. • It is the alteration in the estrogen: progesterone ratio rather than the fall in the absolute concentration of progesterone which is linked with prostaglandin synthesis.
- 20. Prostaglandins: • Synthesis is triggered by— – rise in estrogen level, – glucocorticoids, – mechanical stretching in late pregnancy, – increase in cytokines (IL–1, 6, TNF), – infection, – vaginal examination, – separation or rupture of the membranes. • Prostaglandins enhance gap junction (intermembranous gap between two cells through which stimulus flows) formation.
- 21. Biochemical mechanisms • Once the arachidonic acid cascade is initiated, prostaglandins themselves will activate lysosomal enzyme systems. • The prostaglandin synthesis reaches a peak during the birth of placenta probably contributing to its expulsion and to the control of postpartum hemorrhage. Uterinecontraction Synthesis of PGs through PG synthetase diffuse in myometrium Esterified arachidonic acid Inhibit intracellular cAMP generation Act directly at the sarcoplasmic reticulum Increase local free Ca+2 ions Formation of free arachidonic acid
- 22. Oxytocin and myometrial oxytocin receptors (i)Large number of oxytocin receptors are present in the fundus compared to the lower segment and the cervix. (ii) Receptor number increases during pregnancy reaching maximum during labor. (iii)Receptor sensitivity increases during labor. (iv)Oxytocin stimulate synthesis and release of PGs (E2 and F) from amnion and decidua. • Vaginal examination and amniotomy cause rise in maternal plasma oxytocin level (Ferguson reflex).
- 23. Neurological factor • Both α and β adrenergic receptors are present in the myometrium; estrogen causing the α receptors and progesterone the β receptors to function predominantly. • The contractile response is initiated through the a receptors of the postganglionic nerve fibers in and around the cervix and the lower part of the uterus.
- 24. Hypothalamus sends efferent impulses to posterior pituitary, where oxytocin is stored Posterior pituitary releases oxytocin to blood; oxytocin targets mother’s uterine muscle Uterus responds by contracting more vigorously Afferent impulses to hypothalamus Pressoreceptors in cervix of uterus excited Baby moves deeper into mother’s birth canal Positive feedback mechanism continues to cycle until interrupted by birth of baby
- 26. Uterine Activity During Pregnancy Inhibitors •Progesterone •Prostacycline •Relaxin •Nitric Oxide •Parathyroid hormone-related peptide •CRH •HPL Quiescence Uterotonins Prostaglandins Oxytocin Stimulation Uterotrophins Estrogen •Progesterone •Prostaglandins •CRH Activation Involution Oxytocin •Thrombin Involution
- 27. • The basic elements involved in the uterine contractile systems are— • (a) actin • (b) myosin • (c) adenosine triphosphate (ATP) • (d) the enzyme myosin light chain kinase(MLCK) and • (e) Ca+2ions
- 28. Calcium channel Ca store + Oxytocin + Prostaglandin Ca+ MLCK Extracellular Intracellular Uterine contractions cAMP Oxytocin receptor Phospholipase C
- 29. • Uterine muscles have two types of adrenergic receptors— • α receptors, which on stimulation produce a decrease in cyclic AMP (adenosine monophosphate) and result in contraction of the uterus and • ß receptors, which on stimulation produce rise in cyclic AMP and result in inhibition of uterine contraction.
- 30. PRELABOR • “Lightening”: – Few weeks prior to the onset of labor specially in primigravidae, the presenting part sinks into the true pelvis. – It is due to active pulling up of the lower pole of the uterus around the presenting part. It signifies incorporation of the lower uterine segment into the wall of the uterus. – It is a welcome sign as it rules out cephalopelvic disproportion and other conditions preventing the head from entering the pelvic inlet. • Cervical changes: Few days prior to the onset of labor, the cervix becomes ripe. A ripe cervix is soft, less than 1.5 cm in length, admits a finger easily and is dilatable. • Appearance of false pain
- 31. Labor pains • Throughout pregnancy, painless Braxton Hicks contractions with simultaneous hardening of the uterus occur. • These contractions change their character, become more powerful, intermittent and are associated with pain. The pains are more often felt in front of the abdomen or radiating toward the thighs. • Show: • With the onset of labor, there is profuse cervical secretion. • Simultaneously, there is slight oozing of blood from rupture of capillary vessels of the cervix and from the raw decidual surface caused by separation of the membranes due to stretching of the lower uterine segment. • Expulsion of cervical mucus plug mixed with blood is called “show”
- 32. True labor pains • characterized by – (i) Uterine contractions at regular intervals – (ii) Frequency of contractions increase gradually – (iii) Intensity and duration of contractions increase progressively – (iv) Associated with “show” – (v) Progressive effacement and dilatation of the cervix (vi) Descent of the presenting part – (vii)Formation of the “bag of forewaters” – (viii) Not relieved by enema or sedatives.
- 33. False labor pains are – (i) Dull in nature –(ii) Confined to lower abdomen and groin –(iii) Not associated with hardening of the uterus – (iv) They have no other features of true labor pains as discussed above – (v) Usually relieved by enema or sedative.
- 34. Pains at regular intervals Intervals gradually shorten Duration and severity increases Pain starts in back and moves to front Walking increases the intensity Association between the degree of uterine hardening and intensity of pain Bloody show often present Cervix effaced and dilated Descent of presenting part Head is fixed between pains sedation does not stop true labor. ×Irregular intervals ×No change ×No change ×Pain mainly in front ×No change ×No relationship ×No show ×No change in cervix ×No descent ×Head remains free × efficient sedative stops pains False laborTrue labor
- 35. Dilatation of internal os • With the onset of labor pain, the cervical canal begins to dilate more in the upper part than in the lower, the former being accompanied by corresponding stretching of the lower uterine segment.
- 36. Formation of “bag of waters”: • As it contains liquor which has passed below the presenting part, it is called “bag of waters”. • During uterine contraction with consequent rise of intra-amniotic pressure, this bag becomes tense and convex. • This is almost a certain sign of onset of labor. However, in some cases the membranes are so well applied to the head that the finding may not be detected.
- 37. STAGES OF LABOR: 1st stage 2nd stage 3rd stage 4th stage
- 38. STAGES OF LABOR: • Conventionally, events of labor are divided into three stages: • 1st stage: It starts from the onset of true labor pain and ends with full dilatation of the cervix. It is, in other words, the “cervical stage” of labor. • Its average duration is 12 hours in primigravidae and 6 hours in multiparae.
- 39. 2nd stage: • It starts from the full dilatation of the cervix (not from the rupture of the membranes) and ends with expulsion of the fetus from the birth canal. • It has got two phases— – (a) The propulsive phase – starts from full dilatation upto the descent of the presenting part to the pelvic floor. – (b) The expulsive phase is distinguished by maternal bearing down efforts and ends with delivery of the baby. • Its average duration is 2 hours in primigravidae and 30 minutes in multiparae.
- 40. • Third stage: It begins after expulsion of the fetus and ends with expulsion of the placenta and membranes (after-births). • Its average duration is about 15 minutes in both primigravidae and multiparae. The duration is, however, reduced to 5 minutes in active management. • Fourth stage: It is the stage of observation for at least 1 hour after expulsion of the after-births. • During this period, general condition of the patient and the behavior of the uterus are to be carefully monitored.
- 41. physiology 35
- 42. • UTERINE CONTRACTION IN LABOR: Throughout pregnancy there are irregular involuntary spasmodic uterine contractions which are painless (Braxton-Hicks) and have no effect on dilatation of the cervix .The character of the contractions change with the onset of labor. • pacemaker of the uterine contractions. • Simultaneously, the patient experiences pain which is situated more on the hypogastric region, often radiating to the thighs. • Probable causes of pain are: • (a) Myometrial hypoxia during contractions (as in angina). • (b) Stretching of the peritoneum over the fundus. • (c) Stretching of the cervix during dilatation. (d) Compression of the nerve ganglion. The pain of uterine contractions is distributed along the cutaneous nerve distribution of T10 to L1 • . Pain of cervical dilatation and stretching is referred to the back through the sacral plexus. Good relaxation occurs in between contractions to bring down the intra- amniotic pressure to < 8 mm Hg. Contractions of the fundus last longer than that of the midzone. Intra-amniotic pressure rises > 20 mm Hg during uterine contraction The waves of contraction follow a regular pattern. There is fundal dominance with gradual diminishing contraction wave through midzone down to lower segment which takes about 10–20 seconds. There is good synchronization of the contraction waves from both halves of the uterus.
- 43. • Tonus: It is the intrauterine pressure in between contractions. • The factors which govern the tonus are— – (i) Contractility of uterine muscles – (ii) Intra-abdominal pressure – (iii) Overdistension of uterus as in twins and hydramnios. • Intensity: The intensity of uterine contraction describes the degree of uterine systole. • Intrauterine pressure is raised to 40–50 mm Hg during first stage and about 100–120 mm Hg in second stage of labor during contractions. • In spite of diminished pain in third stage, the intrauterine pressure is probably the same as that in the second stage. • The diminished pain is due to lack of stretching effect.
- 44. • Duration: In the 1st stage, the contractions last for about 30 seconds initially but gradually in duration with the progress of labor. • Thus in the 2nd stage, the contractions last longer than in the 1st stage. • Frequency: In the early stage of labor, the contractions come at intervals of 10–15 minutes. • The intervals gradually shorten with advancement of labor until in the 2nd stage, when it comes every 2–3 minutes.
- 45. RETRACTION: • Retraction is a phenomenon of the uterus in labor in which the muscle fibers are permanently shortened. • (The net effects of retraction in normal labor are: – Essential property in the formation of lower uterine segment and dilatation and effacement of the cervix. – To maintain the advancement of the presenting part made by the uterine contractions and to help in ultimate expulsion of the fetus. – To reduce the surface area of the uterus favoring separation of placenta. – Effective hemostasis after the separation of the placenta.
Editor's Notes
- #3: A famous person once said that the hand that rocks the cradle will rule the world
- #5: She undergoes many anatomical and physiological changes in her body ,but she is only concerned about her baby.
- #9: It may occur prior to 37 completed weeks, when it is called preterm labor Expulsion of a previable live fetus occurs through the same process but in a miniature form and is called mini-labor. A parturient is a patient in labor and parturition is the process of giving birth.
- #10: Delivery may be vaginal, either spontaneous or aided or it may be abdominal.
- #12: Thus, labor in a case with presentation other than vertex or having some complications even with vertex presentation affecting the course of labor or modifying the nature of termination or adversely affecting the maternal and/or fetal prognosis is called abnormal labor.
- #13: Ultrasound confirmation of gestational age[edit] Since the 1970s, ultrasound scans have allowed measurement of the size of developing embryos directly and so allow for an estimation of gestation age. Ultrasound dating is most accurate if undertaken in the first trimester (first 12 weeks of pregnancy) with a 95% error margin of six days.
- #14: In sheep it is clear that maturation of fetal Hypothalamo-hypophyseal adrenal axis during late pregnancy is responsible for iniating labor by inducing changes in pattern of placental steroidogenesis and ultimately by increasing the production of intrauterine PGs. Administration of ACTH or GCs to fetal lamb in utero sheep induces birth before term has been reached. In both humans and monkeys the admin of GCs doesnot bring on labor nor is there evidence to show that fetal cortisol sets off parturition in humans.
- #21: Prostaglandins are the important factors which initiate and maintain labor.
- #22: involved in the synthesis of prostaglandins in the lysosomes of the fetal membranes near term
- #23: Fetal plasma oxytocin level is found increased during spontaneous labor compared to that of mother. Its role in human labor is not yet established
- #24: Although labor may start in denervated uterus, labor may also be initiated through nerve pathways. This is based on observation that onset of labor occurs following stripping or low rupture of the membranes.
- #29: Oxytocin binds receptor and activates phospholipase c. PHC increase intracellular Ca by release of intracellular calcium and promote influx of calcium. Ca binds myosin light chain kinase
- #30: Intracellular Ca ++ → Calmodulin Ca → MLCK → Phosphorylated Myosin + Actin → Myometrial contraction. • Decease of intracellular Ca ++ ++ 2 (or its shift to the storage sites) → dephosphorylation of myosin light chain → inactivation of myosin light chain kinase → Myometrial relaxation.
- #31: The premonitory stage may begin 2–3 weeks before the onset of true labor in primigravidae and a few days before in multiparae. The features are inconsistent and may consist of the following: This diminishes the fundal height and hence minimizes the pressure on the diaphragm . The mother experiences a sense of relief from the mechanical cardiorespiratory embarrassment. There may be frequency of and micturition or constipation due to mechanical factor—pressure by the engaged presenting part
- #34: Inefficient contractions of the uterus or painful spasms of the intestines ,bladder and abdominal wall muscles They are irregular and short and are felt more in the infront than the back The uterus doesnot become stony hard and can be indented with the finger These contractions are inefficient in pushing down the presenting part and donot bring about progressive effacement and dilatation of the cervix. False labor pains can have harmful effect of tiring the patient , so that when true labor does begin she is in poor condition, both mentally and physically They appear few days to a month before term.
- #35: he experience of labor pain varies markedly from woman to woman. It can also vary for the same woman in different parts of the labor and from one labor to another. Nearly all women experience lower abdominal pain during contractions. Many also experience low back pain, either with contractions or, less often, continuously. Women may also feel pain throughout the belly; in the hips, buttocks, or thighs; or in some combination of these locations. Pain may radiate from front to back, back to front, or down the thighs. It may be felt in several areas at once or just in one specific place. Words women use to describe their pain include: cramping, sharp, aching, throbbing, pressing, and shooting. Pain intensity varies widely and generally increases as labor progresses. The sources and sensations of pain are different in the dilation and pushing phases of labor, and your experience may differ substantially as well. The pushing phase may be less painful. Some women reporting intense labor pain prefer not to describe their pain in negative terms. This suggests that the sensation and interpretation of pain may be distinct from each other. There are various reasons why this may be so.
- #37: Due to stretching of the lower uterine segment, the membranes are detached easily because of its loose attachment to the poorly formed decidua. With the dilatation of the cervical canal, the lower pole of the fetal membranes becomes unsupported and tends to bulge into the cervical canal. After the contractions pass off, the bulging may disappear completely.
- #42: During pregnancy there is marked hypertrophy and hyperplasia of the uterine muscle and the enlargement of the uterus. At term, the length of the uterus measures about 35 cm including cervix. The fundus is wider both transversely and anteroposteriorly than the lower segment. The uterus assumes pyriform or ovoid shape. The cervical canal is occluded by a thick, tenacious, mucus plug.
- #43: While there are wide variations in frequency, intensity and duration of contractions, they remain usually within normal limits in the following patterns. During contraction, uterus becomes hard and somewhat pushed anteriorly to make the long axis of the uterus in line with that of pelvic axis.
- #44: During pregnancy, as the uterus is quiescent (inactive), the tonus is of 2–3 mm Hg. During the first stage of labor, it varies from 8–10 mm Hg. It is inversely proportional to relaxation. . The intensity gradually increases with advancement of labor until it becomes maximum in the second stage during delivery of the baby. Intensity is initially influenced probably by hormones but subsequently depend on multiple origin of contractions.
- #45: It is important to note that all the features of uterine contractions mentioned are very effective only when they are in combination.
- #46: Unlike any other muscles of the body, the uterine muscles have this property to become shortened once and for all. Contraction is a temporary reduction in length of the fibers, which attain their full length during relaxation. In contrast, retraction results in permanent shortening and the fibers are shortened once and for all