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Gestational age: 30 weeks old. Embryonic age: Week nr 29. 28 weeks old. The fetus reaches a length of about 38–43 cm (15–17 in). The fetus weighs about 1.5 kg (3 lb 5 oz). The amount of body fat rapidly increases. Rhythmic breathing movements occur, but lungs are not fully mature. Thalamic brain connections, which mediate sensory input, form.
The first ten weeks of gestational age is the period of embryogenesis and together with the first three weeks of prenatal development make up the first trimester of pregnancy. From the 10th week of gestation (8th week of development), the developing embryo is called a fetus.
2.2 Weeks 17 to 25 (3.6 to 6.6 months) 2 ... Old adult; Dying; ... In human prenatal development, fetal development begins from the ninth week after fertilization ...
Group A had 90 fetuses of 9–12 weeks of gestation and the weight varied between 1-14 grams. Group B had 337 fetuses, age 13–16 weeks of gestation with weight variation between 15 and 105 grams whereas the third group had 435 fetuses of 17–20 weeks of gestation with a weight range between 106 and 310 grams.
Human embryonic development covers the first eight weeks of development, which have 23 stages, called Carnegie stages. At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs.
A fetus is a stage in the human development considered to begin nine weeks after fertilization. [4] [5] In biological terms, however, prenatal development is a continuum, with many defining features distinguishing an embryo from a fetus. A fetus is also characterized by the presence of all the major body organs, though they will not yet be ...
The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos. In the human being, only the first 60 days of development are covered; at that point, the term embryo is usually replaced with the term fetus.
At 20 weeks, the fetus is able to implement feedback mechanisms for the production of thyroid hormones. During fetal development, T 4 is the major thyroid hormone being produced while triiodothyronine (T 3) and its inactive derivative, reverse T 3, are not detected until the third trimester. [2]