​which event is characteristic of the period of the fetus
Fetus A fetus is a stage in the prenatal development of viviparous organisms. In human development, a fetus or foetus (/ˈfiːtəs/; plural fetuses or foetuses) is a prenatal human between the embryonic state and birth. The fetal stage of development tends to be taken as beginning at the gestational age of eleven weeks, i.e. nine weeks after fertilization.[1][2] In biological terms, however, prenatal development is a continuum, with no clear defining feature distinguishing an embryo from a fetus. The use of the term "fetus" generally implies that an embryo has developed to the point of being recognizable as a human; this is the point usually taken to be the ninth week after fertilization. A fetus is also characterized by the presence of all the major body organs, though they will not yet be fully developed and functional and some not yet situated in their final anatomical location.
Menarche Menarche (/mɪˈnɑːrkiː/ mi-NAR-kee; Greek: μήν mēn "month" + ἀρχή arkhē "beginning") is the first menstrual cycle, or first menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility.