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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.
Fetal viability refers to a point in fetal development at which the fetus may survive outside the womb. The lower limit of viability is approximately 5 + 3 ⁄ 4 months gestational age and is usually later. [20] There is no sharp limit of development, age, or weight at which a fetus automatically becomes viable. [21]
Embryonic age: Week nr 33. 32 weeks old. The fetus reaches a length of about 40–48 cm (16–19 in). The fetus weighs about 2.5 to 3 kg (6 lb 10 oz)to 6 lb 12 oz). Lanugo begins to disappear. Body fat increases. Fingernails reach the end of the fingertips. A baby born at 36 weeks has a high chance of survival, but may require medical ...
In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. 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 40 weeks.
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]
[4] [5] This is just over nine months. Counting by fertilization age, the length is about 38 weeks. [5] [13] Pregnancy is "the presence of an implanted human embryo or fetus in the uterus"; implantation occurs on average 8–9 days after fertilization. [15]
An Ohio hospital successfully performed its first in utero fetal surgery to repair a birth defect in a nearly 23-week-old fetus, making it one of few elite medical facilities in the U.S. capable ...
The book was often cited as presenting the first images of a live fetus in utero. [14] In fact, Geraldine Flanagan's The First Nine Months Of Life had in 1962 compiled a similar set of fetal images from medical archives. [15] The images played an important role in debates about abortion and the beginning of human life. [16]