occiput transverse to occiput anterior position, which means the infant must rotate from the sideways position so the anterior head faces the buttock of the mother. Extension is the point where the head moves past the pubic symphysis, where it has to curve underneath the birth canal while the anterior head still faces the mother's bottom. External rotation (or Restitution) occurs when the baby pauses after the head passes through the body. During this pause, the infant rotates itself sideways (facing the mother's thigh) to allow for the shoulder to fit though the birth canal. Expulsion is the final step of labor. During this stage, the anterior shoulder moves past the birth canal first then the posterior shoulder. Once both shoulders are out, the baby is delivered through the birth canal completely. While the seven cardinal movements is considered the normal mechanism for labor and delivery of human babies, pelvic sizes and shapes can vary among female humans which can increase the risk of errors in rotations and delivery, especially since these moments are done completely by the baby. One of the biggest issues with the pelvic shape for childbirth is the Ischial spine. Since the ischial spines support the pelvic floor, if the spines are too far apart it can lead to a weakened pelvic floor muscles. This can cause issues as pregnancy progresses, such as difficulty carrying the fetus to full term. Another complication that can occur during human childbirth is shoulder dystocia, where the shoulder is stuck in the birth canal. This can lead to fractured humerus and clavicle of the fetus and hemorrhaging of the mother postpartum. Thus, these neonatal rotations are important in allowing the baby to safely pass through the pelvic and ensure the health of the mother as well. Gestation length and altriciality Gestation length in humans is believed to be shorter than most other primates of comparable size. The gestation length for humans is 266 days, or eight days short of nine months, which is counted from the first day of the woman's last menstrual period. During gestation, mothers must support the metabolic cost of tissue growth, both of the fetus and the mother, as well as the ever-increasing metabolic rate of the growing fetus. Comparative data from across mammals and primates suggest that there is a metabolic constraint on how large and energetically expensive a fetus can grow before it must