Final answer:
The term for the number of pregnancies that reached 20 weeks of gestation is 'parity' or 'gravida,' encompassing all pregnancies that reached the stage of fetal viability.
Step-by-step explanation:
The term that refers to the number of pregnancies that reached fetal viability, which is the point in fetal development where the fetus is likely to survive outside the uterus, is called 'parity' or 'gravida'. This count includes all pregnancies that reach 20 weeks of gestation (regardless of whether the fetus was born alive or not). It is important to distinguish this from the number of fetuses, as a single pregnancy could result in multiple fetuses. Fetal viability is crucial since it represents a significant milestone in gestation, where the chances of the fetus surviving increase significantly, particularly after 26 weeks of gestation where more than 90 percent of babies survive if they receive necessary medical care.