October 24, 2024 Labor is the process by which the body of a pregnant woman prepares for birth . It is characterized by hormonal, physical and emotional changes that culminate in painful and regular uterine contractions, cervical dilation and birth of the baby. Labor can be divided into 3 periods or stages: 1 st stage or dilation period 2 nd stage or expulsion period 3 rd stage The duration and evolution of these periods depend on multiple maternal and fetal factors . Cervical dilation period The dilation period, or 1st stage, goes from the beginning of labor until complete dilation and comprises two phases: The latent phase , characterized by slower dilation, generally up to 6 cm dilation; The active phase , with faster dilation. Dilation period changes In 20% of births, there are changes to the normal dilation period, which can be of two types: Prolonged labor , which is defined as dilation of less than 1-2 cm every 2 hours, after reaching 6 cm of dilation; Labor arrest , which is defined by the absence of dilation for 4-6 hours, in pregnant women with 6 or more cm of dilation and ruptured membranes. Changes in the dilation period are more frequent in the first birth. They can have different causes: uterine (low uterine contractility), fetal (large or poorly positioned fetus), related to the mother's pelvis, or a mixture of several factors. There is also a genetic component. Assessing whether or not labor is occurring normally is a key factor in intrapartum care. Risks of cervical dilation period changes Prolonged labor and labor arrest have maternal and fetal risks: In pregnant women , the risk of chorioamnionitis (infection of the placenta and amniotic fluid), instrumented birth (forceps and suction cup), damage to the anal sphincter, cesarean section, postpartum hemorrhage, urinary retention and endometritis (infection of the uterus) increases; In newborns , the risk of fetal distress, infection, respiratory problems and eventual admission to the neonatal care unit, respiratory distress syndrome, sepsis (generalized infection) and neonatal asphyxia increases. In the case of prolonged labor, the use of oxytocin and amniotomy (membrane rupture) is recommended. In cases where labor stops, a cesarean section is recommended. Expulsion period The expulsive period, or 2nd stage, lasts from complete dilation until the birth of the baby . Its duration and evolution depend on factors such as : The size and shape of the mother pelvis; The maternal position; The frequency and intensity of contractions; The quality of expulsive efforts; The number of previous births; The use of epidural analgesia; The size and position of the fetus. Expulsive efforts are the voluntary contraction of the diaphragm and abdominal wall muscles. They are a response to the stimulation of the pelvic floor by the baby head, but also an effort that the pregnant woman initiates voluntarily. There are several techniques described for “pushing”. None is superior to the others with regard to maternal (eg, duration of the expulsive period, rate of episiotomy and lacerations) and neonatal (eg, Apgar score) outcomes. Expulsion period changes Most pregnant women deliver their baby 60-90 minutes after initiating expulsive efforts, regardless of the number of previous births or whether or not they have had epidural analgesia. Whenever this period exceeds 3-4 hours in a first birth or 2-3 hours in subsequent ones, it is considered to be a prolonged or prolonged expulsion period . Depending on the reason, a prolonged expulsive period may be an indication for administering oxytocin, manual rotation of the presentation (fetal head), instrumented delivery (suction cup or forceps) or cesarean section. Risks of expulsion period changes A prolonged expulsive period has maternal (postpartum bleeding and infection), neonatal (higher rate of admission to intensive care and neonatal sepsis) and surgical risks (higher risk of uterine laceration in case of cesarean section). Several interventions have been described, namely different expulsive effort techniques, maternal positioning and pelvic floor exercises, but there is no scientific evidence demonstrating their effect in reducing the duration of the expulsive period or the rate of instrumented births. 3 rd period The 3 rd stage of labor is the period lasting from the baby birth to the delivery of the placenta . The umbilical cord must be clamped 30 to 60 seconds after birth , and at this time 75% of the blood available in the placenta has been transfused. The position of the newborn, below or above the placenta, does not appear to affect the volume of the placenta-newborn transfusion so that it can be placed in the maternal abdomen. The main advantage of delayed umbilical cord clamping is to achieve greater iron reserves at 6 months of age, which can improve the baby's neurodevelopment. In the mother, delayed cord clamping has no impact. The main disadvantages are the increased risk of neonatal jaundice requiring phototherapy, polycythemia in small newborns and lower blood volume for stem cell collection (if applicable). A mother or baby hemodynamically unstable are contraindications for delayed cord clamping, as occurs in situations of placental abruption or cord rupture, among others. After the fetus is delivered, the uterine muscle contracts, separating the placenta from the uterus, leading to its expulsion . The active management of this process, when compared to the expectant attitude, reduces the risk of serious hemorrhage. This content was prepared by the Gynecology-Obstetrics team at Hospital da Luz. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
