The Physiology of the First Stage of Labour - Essay Example

?Labour: Questions and Answers Describe the physiology of the first stage of labour? Labour may be defined as a physiologic process during which various products of conception like fetus, umbilical cord, membranes and placenta are expelled from the uterus outside. There are basically 3 stages of labour. All the stages occur as a continuous process. Several changes in the biochemistry of the connective tissues along with gradual effacement and dilatation of the cervix leads to rhythmic uterine contractions which are of appropriate intensity, frequency and duration. First stage of labour begins with uterine contractions that are regular and ends with complete dilatation of the cervix, i.e. 10 cm. This stage may be divided into early latent phase, an active phase and a transitional phase. During the latent phase, the uterine contractions are irregular and mild. The cervix begins to shorten and soften. The cervix is dilated 1-4cm. Contractions of the uterus may or may not be regular and may be associated with backache, abdominal cramps, show, rupture of membranes, mucoid vaginal discharge and passage of the mucus plug. Active phase begins when the cervix is 3-4 cm dilated. The dilatation rapidly increases and presenting fetal part descends. The uterine contractions are much stronger and last for longer period, approximately 40-45 seconds. They are also more frequent. Contractions may be accompanied by pain in this stage. The cervix is dilated upto 8cm. This phase is followed by the transitional stage. Cervix dilatation is 8-10cm. The contractions of the uterus are stronger and of longer duration, 50-60seconds. Other symptoms in this stage are discomfort, hiccups, irritable abdomen, behavioural changes, restlessness, nausea and vomiting, increased perspiration, heavy show that is profusely dark, rupture of membranes, low back ache and sensation of stretching in deep pelvis. The first stage of labour ends when the cervix is dilated at 10 cm. In the primigravida, this stage lasts about 12 hours. In multigravida, the duration is about 7 hours. Friedman has divided active phase into phase of acceleration, followed by maximum slope phase and eventually a deceleration phase (Fraser and Cooper, 2006). The uterine activity is minimal during pregnancy. As the end of gestation approaches, procontractile influences increase and nullify the action of factors which keep the uterus and cervix quiescent. At term, cortisol production of fetus increases. This causes increase in the production of estrone and estradiol and decreased production of progesterone from placenta. This amounts to increase in uterine activity because, basically, while progesterone suppresses the activity of the uterus, estradiol increases it. Increased production of prostaglandins occurs which contribute to increased activity of the myometrium. All these changes amount to release of oxytocin and other hormones like CRH, activin A, follistatin, relaxin and hCG, which further increase myometrial activity (Fraser and Cooper, 2006). Towards term, softening of cervix occurs due to decrease in collagen and increase in proteolytic enzymes. This partly occurs due to increased production of hyaluronc acid which decreases the affinity between collagen and fibronectin. Due to affinity of hyaluronic acid towards water, the cervix gradually softens and ripens. Even cervix contracts from the point of dilatation of 3-4 cm. However, in the active phase of labour, dilatation of cervix mainly occurs due to passive stretching of contractions of the uterus (Fraser and Cooper, 2006). The uterine pressures in first stage of labour rise to 20-30mmHg during contraction. The contractions occur every 10-15 minutes and lasts for 30-40 seconds. The intensity of contractions increases to a maximum of 50mmHg. Pain develops when the amniotic pressures increase beyond 25mmHg. Uterine contractions cause dilatation and effacement of the cervix due to shortening of the fibers of the myometrium in the upper segment of the uterus. This is called retraction. The lower segment of the uterus elongates and thins out gradually and the junction between the lower and the upper segments of the uterus rises into the abdomen. Contraction of the uterine body, along with relaxation of the cervical circular fibers is known as uterine polarity. Both the processes are interdependent and actually mark the commencement of labour (Fraser and Cooper, 2006). The pacemaker for contractions is in the left uterine cornua and the contractions spread downwards. The contractions first occur in the uterine fundus. Fundal contractions are much stronger and last much longer than the contractions in other parts of the uterus. This is known as fundal dominance. Fundal dominance plays a crucial role in the progression of the dilatation and also effacement of the cervix. During each contraction, fundal contraction force is transmitted to the upper pole of the fetus, then down the long axis of the fetus and to the presenting part that is applied to the cervix. This is known as fetal axis pressure. This is more significant in the second stage of labour (Symonds, 2003). During the first stage of labour, the presenting part of the fetus does not descend much. Amniotic fluid accumulates in the membranes in such a a way the a bad of fore waters is formed. This may or may not get ruptured. If it does, then it becomes cervix dilator. The fore waters help as cushion to the baby. They also help transmission of the pressure of the uterine contractions to internal os of the cervix, which is the point of least resistance (NICE, 2007). What are the signs of second stage of labour and outline the principle of care? The second stage of labour follows the first stage. It begins when the cervix is dilated completely and ends with the delivery of the fetus. In this stage, the membranes of the fetus are usually ruptured and the uterus exerts pressure on the fetus. The pressure is firm. The contractions of the uterus are very frequent and may be just 1-2 minutes apart, gradually they become expulsive in nature. During exhaling, an expulsion grunt occurs. The uterus adapts to the volume of the contents present in it as the fundus gradually expels the fetus. The lower segment becomes stretched to accomodate the passage of the fetus. In the beginning of the second stage, the diaphragm and the abdominal muscles are voluntary. However, as the head of the fetus presses against the perineum, the muscles begin to act involuntarily. Pressure against the rectum causes an urge to bear down and defecate. Rectal bulging is prominent along with flattening of perineum. Amnesia between contractions increases. The skeletal pelvis gives way for passage of the fetus. As expulsion occurs, the cervix slips back over the parts of the fetus that come successively. The muscles of the pelvic floor and also the perineum stretch. They may tear in the midline and an episiotomy may be done (Fraser and Cooper, 2006). When the membranes rupture, the leakage of amniotic fluid lubricates the passage of delivery. The intensity of uterine contractions and also the contractions of the muscles of the abdomen get transmitted to the fetus and force the presenting part through the birth canal. The steps in the expulsion of the fetus are as follows: The fetus first gets engaged. During engagement, the presenting part gets adapted to the pelvic inlet that is constricted. Then the fetus descents. During descent, the presenting part of the fetus is forced through various planes of the pelvic floor. However, there is not much change in the original position. After this, the flexion of the fetus is further increased and this is known as flexion. Resistance offered by muscles of the pelvic floor causes internal rotation. This is followed by extension when the birth of the presenting part occurs. After that, restitution or external rotation occurs and the baby is born (NICE, 2007). The second stage of labour may be divided into passive and active stages. In the passive stage, the cervix is dilated, but involuntary expulsive contractions are absent. In the active stage, the baby is visible, expulsive contractions are present and there will be active effort by the mother after complete dilatation of the cervix even in the absence of contractions that are expulsive. The duration of second stage is 3 hours in primiparous women and 2 hours in nulliparous women. Principles of care in second stage: 1. Oxytocin administration: In nuliparous women, inadequacy of contractions at the onset of second stage warrants use of oxytocin. 2. Observations: Pulse rate and blood pressure must be checked hourly. Temperature should be measured 4th hourly. Vaginal examination must be measured hourly after onset of second stage of delivery. The frequency of contractions must be documented every half-an-hour. Other observations that must be made include frequency of emptying of bladder, behaviour of the woman, the psychological and emotional needs of the woman, effectiveness of pushing, fetal well being, intermittent fetal heart auscultation, position of the woman, coping strategies, hydration and relief of pain. Fetal monitoring must be done by checking fetal movements, listening to fetal heart rate using sonicaid and pinnard every 5 minutes after every contraction for a minute. 3. Position and pushing: The woman must adopt any comfortable position except the supine and the semi-supine position. She should push only when she has the urge to do so. 4. Interventions to reduce trauma to the perineum: No perineal massage must be performed and any technique: 'hands on' or 'hands poised' technique can be used. Episiotomy is done only when needed like fetal compromise threat or application of instrumentation. Mediolateral episiotomy is the choice. Prior to episiotomy effective analgesia must be provided (NICE, 2007). How would you advise a woman that she was indecisive about the 3rd stage? Third stage of labour is the stage beginning from the birth of the baby and ending at complete expulsion of the placenta and the fetal membranes. This phase can be managed both actively and physiologically. Active management: In this type of management, the patient is administered uterotonic drugs. The clamp is applied early to the cord and the cord is cut. The cord is pulled using controlled traction. The most commonly used uterotonic agent is oxytocin (10 IU is administered intramuscularly). Physiological management: The patient is not administered any uterotonic drug. The cord is not clamped until cessation of pulsation and placenta is delivered only through effort of the mother. Massaging of the uterus and breast feeding after delivery enhances tonicity of the uterus and decreases bleeding. Advice: Women must be advised that active management reduces the third stage and also decreases the risk of maternal hemorrhage. They must also be advised that administration of uterotonic drugs like synometrine is associated with side effects like hypertension, head ache, nausea and vomiting. However, those who are at low risk of postpartum hemorrhage and choose for physiological management must be supported. In these patients, active management is instituted in case of hemorrhage, delay in the delivery of the placenta of more than one hour and maternal wish to shorten the stage. Palpation of the uterus and pulling of the cord must be done only after administration of oxytocin (NICE, 2007). How is bleeding controlled following the delivery of the placenta? Maternal blood loss following expulsion of the placenta is limited mainly by the contraction of the uterus. Normally the blood loss in less than 600ml. Upto 800ml is considered as normal. Beyond that is considered as post partum hemorrhage. Postpartum hemorrhage mainly occurs when tonicity of the uterus is lacking or deficient. Tonicity of the uterus is maintained by contraction of myometrial fibers of the uterus. The myometrium has 3 layers of fibers, the outer layer, the middle layer and the inner layer. The inner layer or the internal layer is made up of smooth muscle fibers which are arranged in a longitudinal and circular manner. The middle layer fibers are arranged in all types of patterns. The outer layer fibers are longitudinally arranged and have some elastic fibers. All these fibers contract after expulsion of placenta and prevent further uterine blood loss (Smith, 2010). In all deliveries, risk factors for postpartum hemorrhage must be identifed. Antenatal risk factors are previous history of postpartum hemorrhage or retention of placenta, maternal hemoglobin of less than 8.5g/dl at the time of onset of labour, BMI of more than 35kg/m2, multiparity (more than 4), history of antepartum hemorrhage, overdistended uterus either due to fetal macrosomia, multiple pregnancy or polyhydrmanios, presence of existing abnormalities of the uterus, elderly primi and low-lying placenta. Intrapartum risk factors include prolongation of any stage of labour, induced labour, use of oxytocin, precipitate labour and operative birth. Presence of any of these risk factors warrants delivery of baby in a hospital setting and active management of third stage of labour (Smith, 2010). In case of postpartum hemorrhage, uterus must be massaged, intravenous fluids must be admnistered and the patient must be given uterotonics like intravenous oxytocin, intravenous ergometrine, combination of oxytocin and ergometrine intravenously (syntometrine), misoprostol or intramuscular carboprost. Which of these is the best uterotonic agent is yet unclear (NICE, 2007). What are the routine blood tests that are offered at booking to women and why? The routine blood tests that are offered at booking to pregnant women are hemoglobin, blood group and antibodies, and tests to detect rubella, hepatitis-B, syphilis, HIV and blood disorders sickle cell anemia and thalassemia. Hemoglobin is tested to screen for anemia. Detection of anemia in early stages provides enough time to treat. The desired hemoglobin level is more than 11g/100ml. Blood grouping and Rh-D testing must be done along with atypical red-cell alloantibodies. Non-sensitised women with Rh-D negative status must be administered anti-D prophylaxis antenatally routinely. Screening for sickle cell anemia and thalassemia must be done as early as possible to take necessary and appropriate measures as early as possible. Hepatitis B status must be screened for effective postnatal interventions to decrease risk of mother-to-child transmission. HIV must be checked to take measures for proper antenatal interventions in order to decrease transmission of infection from mother to child. Identification and treatment of syphilis in early stages is beneficial to the baby and the mother. Rubella must be screened for because it is associated with increased risk of congenital malformations (NICE, 2008). What are the screening tests and why carry them out? Screening tests are those tests which are performed to detect certain diseases in the mother or anomalies in the baby so that early identification and appropriate treatments and measures can be initiated to provide the best benefits for both the mother and the baby. Screening tests can be categorized into: 1. Screening for hematological diseases: Screening is done for anemia, blood grouping and alloantibodies to red cells and hemoglobinopathies. 2. Screening for fetal anomalies: Fetus is screened for anomalies between 18- 21 weeks of gestation. This includes fetal echocardiography. 3. Screening for Down syndrome: Screening is preferably done before 14 weeks of gestation. The combined test, which includes nuchal translucency, pregnancy-associated plasma protein-A and beta-human chorionic gonadotrophin must be done. In those in whom nuchal translucency cannot be tested, triple or quadruple tests must be performed. 4. Screening for infections: Routine screening for aymptomatc bacteriuria must be done. Other tests to detect infections include chlamydia, cytomegalovirus, Hepatitis B, Hepatitis C, HIV, Rubella, syphilis and toxoplasmosis. 5. Screening for clinical conditions: Diabetes and preeclampsia are 2 conditions which are routinely screened. (NICE, 2008) With reference to relevant physiology explain the significance of examination of the placenta and membranes? Examination of the placenta and membranes provides valuable information about the health of the fetus, cause of preterm delivery, fetal growth retardation, impact of maternal disease on fetus and neurodevelopmental impairment. Such an examination helps in various legal issues like chronic vrs acute stress insult, diagnosis of specific causes of adverse outcomes of pregnancy, identification of zygosity and identification of potential recurrent disorders (Roberts et al, 2010). A pregnant woman who is low risk and at full term is in early labour at home. She telephones you for advice about coping with the pain. What advice would the midwife give to this woman? Gentle exercise, posture and relaxation techniques and breathing techniques are useful in early labour pain management. Warm baths also help. Some massaging also helps (NICE, 2007). With reference to transition to extra uterine life, describe and apply the physiology underpinning the Apgar score. Soon after birth, the placental blood flow to the baby is terminated because of clamping of the umbilical cord. Just before clamping, about 300ml per minute of extra blood gets shunted into the systemic circulation. This causes activation of stretch receptors and release of catecholamines. These hormones increase breathing movements. Before birth, there is no gas exchange n the lungs and lungs receive very little blood flow. Lungs also produce lots of fluid and hence the lungs are filled with fluid. Soon after birth, gas exchange begins in the lungs. Lungs receive 100 percent of cardiac output. the produce only minimal fluid and hence have very little fluid in them. Decrease in fluid production occurs due to catecholamine production. Breathing causes an increase in Blood PO2. It also decreases the pulmonary vascular resistance, indirectly opening the pulmonary vessels and decreasing the intrathoracic pressure. Failure of smooth respiratory transition leads to tachypnea, grunting, flaring, retractions and cyanosis. This is the basis for APGAR scoring (Fraser and Cooper, 2006). References Fraser, D.M., and Cooper, M.A. (2006). Myles' Textbook for Midwives 15th edition. London: Churchill livingston NICE. (2007). Intrapartum Care. Retrieved on 25th January, 2011 from http://www.nice.org.uk/nicemedia/live/11837/36280/36280.pdf NICE. (2008). Antenatal Care. Retrieved on 25th January, 2011 from http://www.nice.org.uk/nicemedia/live/11947/40115/40115.pdf Roberts, D.J., Lockwood, C.J., and Barss, V.A. (2010). Gross examination of the placenta. Retrieved on 25th January, 2011 from http://www.uptodate.com/contents/gross-examination-of-the-placenta Symonds, E. M. (2003). Essential Obstetrics and Gynaecology, 4th ed. Edinburgh: Churchill Livingstone. Smith, J.R. (2010). Postpartum Hemorrhage. Emedicine from WebMD. Retrieved on 25th January, 2011 from http://emedicine.medscape.com/article/275038-overview Read More