foreign also called parturition describes the hard work of delivering a baby it specifically refers to the process which starts with uterine contractions which cause cervical changes which allow the fetus to be delivered vaginally and ends with the delivery of the placenta labor typically begins at some point when the fetus is considered full term between 37 and 42 weeks gestation in the third trimester before Labor starts a woman might have a plug of mucus and blood fall out of the opening to the cervix sometimes called the bloody shell other times the amniotic sac might rupture sometimes called water breaking either of these can trigger the onset of Labor and so-called true labor contractions these guys have to be distinguished from the milder and ineffective false labor contractions also called Braxton Hicks contractions or sometimes called practice contractions once they start true labor contractions progress in frequency duration and intensity and they can feel like waves that build up to a peak intensity and then gradually decrease the contractions pull on the thick tissues of the cervix causing it to a face or get thinner and also dilate or open up so then the fetus can leave the uterus and enter the world from the moment true contractions begin to the baby's delivery usually takes about 12 to 18 hours for a first-time pregnancy and about half that time for subsequent pregnancies although as any mother knows this time can vary a lot even though labor is a continuous process it can be broken down into three stages additionally this first stage is subdivided into two phases the first phase is the early phase or latent phase and usually lasts up to 20 hours or until the cervix dilates to six centimeters at first there are irregular contractions that occur every 5 to 30 minutes and last about 30 seconds each causing the cervix to dilate from zero centimeters to about three centimeters and a face from about zero percent to thirty percent then regular contractions follow they happen every three to five minutes and last about a minute or more and this causes the cervix to dilate from three centimeters to about six centimeters and a face up to about 80 percent this marks the beginning of the active phase of Labor during which the cervix dilates from 6 to 10 centimeters and a faces to a hundred percent contractions are very intense lasting between 60 to 90 seconds each with only 30 seconds to two minutes of rest in between so sometimes they can even overlap a bit with one contraction beginning before the previous one is done also the amniotics ACT often ruptures at this point if it hasn't already now that the cervix is fully dilated we enter the second stage of Labor and this can be thought of as the pushing stage during this stage the critical thing is for the baby and in particular the baby's head to navigate through the maternal pelvis and this depends on the three p's power passenger and Passage power refers to the forceful uterine contractions passenger refers to the fetus and passage refers to the route that the fetus has to travel through the Bony pelvis in fact the relationship between the baby's head and the Bony pelvis is so critical that human babies have evolved with unfused skulls just so their head can be as large as possible and still successfully and safely make that Passage through the pelvis into the world now there are a few factors that determine how easy this passage is for the fetus first is fetal size the critical Factor here is the size of the fetal head also there's fetal attitude which refers to the way that the fetal body is flexed not its personality when labor starts the fetus is normally fully flexed which means the chin is on the chest and they have a rounded back with flexed arms and legs in this position the smallest diameter which is referred to as a suboccipital brigmatic diameter presents of the pelvic Inlet larger fetuses and those that aren't completely flexed have more difficulty making it through the passage next there's fetal lie which describes how the fetus is positioned in the uterus a longitudinal fetal lie is ideal where the long axis of the fetus which is its spine lies along the maternal long axis the mom's spine the fetus can also be transverso where the fetal spine is perpendicular to Mom's spine or it can be oblique where it's slightly at an angle and these two positions can impede the progression of Labor finally there's fetal presentation which refers to the first fetal part called the presenting part to descend into the pelvic Inlet cephalic or head first is the first type and furthermore the most common and optimal presentation for easy delivery is a type of cephalic presentation called vertex which includes complete flexion of the head as well also there's breach presentation which is head up so the bottom feet or knees present first as well as shoulder where the shoulders present first to make it through the passage the fetus makes several positional changes which are called Cardinal movements or mechanisms of Labor initially there's descent which is a downward movement of the fetus into the pelvic Inlet the degree of descent is called the fetal station which is described in terms of the relationship of the presenting part to Mom's ischial spines the fetus moves from the pelvic Inlet which is at about -5 station down to the ischial spines which is station zero and this position is called engagement then there's flexion where the fetal chin presses against its chest as its head meets resistance from the pelvic floor next there's internal rotation where the fetal shoulders internally rotate by 45 degrees so that the widest part of the shoulders are in line with the widest part of the pelvic Inlet after the fetal head passes under the symphysis pubis which is at about plus four station there's extension which is where the fetal head will change from flexion to extension and then they move to about plus five station and emerge from the vagina after the delivery of the head there's restitution where the head externally rotates so that the shoulders can pass through the pelvic outlet and under the symphysis pubis and finally there's expulsion where the anterior shoulder slips under the symphysis pubis followed by the posterior shoulder and then finally followed by the breast of the body this marks the end of the second stage of Labor the third stage of Labor occurs after the baby has been delivered an evolved delivery of the placenta after the babies delivered the uterus contracts firmly and the placenta begins to separate from the uterine wall it's then carefully removed to ensure that there are no placental remnants left in the uterus sometimes several hours after delivery is called the fourth stage because there are major physiologic changes like adaptation to the blood loss and the start of uterine involution where the uterus begins returning to its pre-pregnant stage all right as a quick recap labor is composed of three stages the first stage starts with true labor contractions and ends when the cervix is completely effaced and dilated the second stage is the pushing stage which ends with the birth of the baby the third stage ends with delivery of the placenta