There are some variations, but the most commonly used fetal station system today assigns a value of -5 to the pelvic inlet and a value of +5 to the pelvic outlet. In order to chart the position of the fetus as it moves through the birth canal, a system of fetal stations was devised many years ago and is still in use today. The orientation of the long axis of the pelvic inlet and pelvic outlet will come into play when we examine the cardinal movements later in the presentation. The long axis goes from the front to the back, the pelvic outlet is deeper than it is wide. In other words, the pelvic inlet is wider than it is deep.Ĭhanging our view to the bottom of the pelvis, we can see that the situation for the pelvic outlet is the opposite of that of the inlet. The long axis of the pelvic inlet goes from left to right. Viewing the pelvis from above, the yellow line highlights the outer border of the pelvic inlet. In relation to how the cardinal movements facilitate passage of the fetus through the birth canal, it is important to note one key anatomical difference between the pelvic inlet and the pelvic outlet. The fetus enters the birth canal at the pelvic inlet and exits through the pelvic outlet. The pelvic outlet is described by a line going from the bottom of the pubic bone to the tip of the sacrum. The pelvic inlet is described by a line going from the top of the pubic bone to the top of the sacrum. While the lowest part of the mother’s spine, the sacrum makes up the back (posterior) wall. Viewing the fetus and the maternal pelvis in a cross-sectional view from the mother’s right side, the front (also known as the anterior) border of the birth canal is provided by the mother’s pubic bone. To better understand the significance of the cardinal movements, let’s do a brief review of maternal pelvic anatomy. The cardinal movements in labor are so named because they are considered essential to successful navigation by the fetus of the maternal birth canal. Cal Shipley with a review of the seven cardinal movements in labor. And the head of the baby is born.This is Dr. Fifth step – ExtentionĪs fetal occiput slip below the pubic arch (which is also called crawling), the fetal head began to extend. But the shoulder does not rotate along with the head of the fetus. it causes the back of the baby’s head to rotate to anterior from its original transverse position. Forth step – Internal rotationĪs uterine contraction increases and fetal occiput advance through the maternal pelvis, it gets resistance from the maternal pelvic floor. It reduces anteroposterior diameter which makes it easier to pass through the pelvic bone. Flexion usually occurs due to resistance of the pelvic floor. it helps the baby to go down through the pelvic bone easily. The lowest diameter of the baby head is when the baby flexes its head. Decent is usually occurred after labor start due to uterine contraction and maternal pushing down effort. This is the time where your baby head moves down into the pelvis. If this is your first pregnancy, the baby head might be engaged even before the labor started. This is the time when the baby head entered the mother’s pelvis (usually in a transverse position).
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