Final answer:
The expulsion of the fetus before 20 weeks is known as a spontaneous abortion, or commonly, a miscarriage.
Step-by-step explanation:
The expulsion of the fetus before 20 weeks is known as a spontaneous abortion or miscarriage. This event occurs when the fetus cannot develop properly, leading to a natural termination of the gestation. A voluntary termination is known as an abortion, which can be legally regulated and may be performed for various reasons, including medical necessity. The term for a birth that occurs after the 20th week but results in a baby born without signs of life is called a stillbirth. An ectopic pregnancy occurs when a fertilized egg implants outside the uterus, most commonly in a fallopian tube, and preterm birth refers to a baby being born alive before 37 weeks of pregnancy are completed.