A fertilized egg is referred to as an embryo until it reaches what stage?

A fertilized egg is termed an embryo until it reaches the fetal stage, which is referred to as a fetus. This transition typically occurs after about eight weeks of development post-fertilization. During the embryonic stage, the developing organism undergoes critical initial developments, including the formation of major organs and systems. Once this stage is complete, and the developing baby reaches a more advanced state of development, it is classified as a fetus.

The other options do not represent stages of development but rather locations or structures related to pregnancy. The uterus is the organ where the embryo implants and grows, the placenta is an organ that develops during pregnancy to provide nourishment and waste removal for the fetus, and the womb is a more colloquial term often used interchangeably with the uterus. However, none of these signify the developmental transition from embryo to fetus.