Final answer:
A fetus positioned with its buttocks or feet first is in a breech presentation. Today, most breech births are delivered by Caesarian section due to safety concerns.
Step-by-step explanation:
The term that refers to a fetus in the buttocks or feet-first position is known as a breech presentation. In this type of birth, the baby's buttocks and feet are positioned to descend through the birth canal first, as opposed to the more common head-first position. In a complete breech, the legs of the fetus are crossed and pointed downward, whereas in a frank breech, the legs are flexed at the hip and extended toward the shoulders. Historically, breech presentations were often delivered vaginally, but today, a Caesarian section is typically performed to ensure safety for both the mother and child.
During the second trimester, specifically weeks 16-20, quickening, or the sensation of fetal movements, can be felt by the pregnant person. The fetus's skin is protected by a waxy substance named vernix caseosa and covered with a fine hair called lanugo, which is usually shed as the fetus grows. By the time of birth, the fetus typically loses the confined fetal position and has grown to an average length of approximately 51 cm (20 inches).
The preferred orientation for childbirth is the vertex presentation, with the occiput anterior vertex more conducive for an easier vaginal birth. However, in the case of a breech presentation, the delivery method has shifted more towards Caesarian section for the safety and health of both the newborn and the mother.