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Human embryonic development or human embryogenesis is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of development. In biological terms, the development of the human body entails growth from a one-celled ...
A human fetus, attached to placenta, at three months gestational age. In humans, the fetal stage starts nine weeks after fertilization. [7] At this time the fetus is typically about 30 millimetres (1 + 1 ⁄ 4 in) in length from crown to rump, and weighs about 8 grams. [7] The head makes up nearly half of the size of the fetus. [8]
Gestation. Drawing of a fetus in utero. Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). [ 1] It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for ...
At this stage, a fetus is about 30 mm (1.2 inches) in length, the heartbeat is seen via ultrasound, and the fetus makes involuntary motions. [47] During continued fetal development, the early body systems, and structures that were established in the embryonic stage continue to develop. Sex organs begin to appear during the third month of gestation.
Gestational age: 3 weeks and 0 days until 3 weeks and 6 days old. 22–28 days from last menstruation. Embryonic age: Week nr 2. 1 week old. 8–14 days from fertilization. Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into the uterine lining. They will eventually form the placenta and embryonic membranes.
In human pregnancy, prenatal development is also called antenatal development. The development of the human embryo follows fertilization, and continues as fetal development. By the end of the tenth week of gestational age, the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where ...
Gestational age. In obstetrics, gestational age is a measure of the age of a pregnancy taken from the beginning of the woman's last menstrual period (LMP), [ 1] or the corresponding age of the gestation as estimated by a more accurate method, if available. Such methods include adding 14 days to a known duration since fertilization (as is ...
Active and quiet periods for the fetus do not correspond to those of the mother; fetuses are most active from 9 a.m. to 2 p.m. and again from 7 p.m. to 4 a.m. [21] During the last four to six weeks before birth, most of the fetus's kicking and jabbing movements occur while it is sleeping lightly. [22]