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A human fetus, attached to placenta, at three months gestational age. In humans, the fetal stage starts nine weeks after fertilization. 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. The head makes up nearly half of the size of the fetus.
Embryonic development in the human, covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a fetus. The eight weeks have 23 stages. Human embryology is the study of this development during the first eight weeks after fertilization. The normal period of gestation (pregnancy) is about nine months or ...
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. 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.
Fetal viability is the ability of a human fetus to survive outside the uterus. Viability depends upon factors such as birth weight , gestational age, and the availability of advanced medical care . In low-income countries , more than 90% of extremely preterm newborns (less than 28 weeks gestational age ) die due to a lack of said medical care ...
The fetus starts producing leukocytes at 2 months gestational age, mainly from the thymus and the spleen. Lymphocytes derived from the thymus are called T lymphocytes (T cells), whereas those derived from bone marrow are called B lymphocytes (B cells). Both of these populations of lymphocytes have short-lived and long-lived groups.
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.
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 ...
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 ...