Final answer:
The number of pregnancies delivered after 20 weeks is referred to as fetal viability, which indicates that the fetus is capable of surviving outside the uterus with medical support. Fetal viability is generally associated with the 24 to 25 week mark. Full-term development is reached after a 40-week gestation period.
Step-by-step explanation:
The number of pregnancies delivered after 20 weeks is referred to as viability of the fetus. The concept of fetal viability is crucial because it represents the stage where the fetus has developed sufficiently to have a reasonable chance of surviving outside the womb. Commonly, medical professionals consider the threshold for viability to be around 24 to 25 weeks of gestation, where the survival rate is significantly higher with medical assistance.
The third trimester is marked by rapid fetal growth and weight gain which is crucial for maintaining a stable body temperature post-birth. During this time, important developmental milestones such as myelination of nerves and production of surfactant in the lungs take place. The former is important for the proper functioning of the nervous system, and the latter helps with lung function after birth.
By the end of a full-term 40-week pregnancy, the fetus reaches full-term development, characterized by significant brain development, and achieves the size and weight necessary for a newborn. During labor, which signifies the end of the gestation period, there are three key stages: dilation of the cervix, delivery of the baby, and delivery of the placenta.