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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 ...
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]
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.
An ultrasound showing an embryo measured to have a crown-rump length of 1.67 cm and estimated to have a gestational age of 8 weeks and 1 day. Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump).
Newborns typically lose 7–10% of their birth weight in the first few days, but they usually regain it within two weeks. [17] During the first month, infants grow about 1 to 1.5 inches (2.5 to 3.8 cm) and gain weight at a rate of about 1 ounce (28 g) per day. [17] Resting heart rate is generally between 70 and 190 beats per minute. [18]
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 36 weeks.
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. [48] 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.
Stages in prenatal development, with weeks and months numbered from last menstruation. In humans, the usual definition of preterm birth is birth before a gestational age of 37 complete weeks. [94] In the normal human fetus, several organ systems mature between 34 and 37 weeks, and the fetus reaches adequate maturity by the end of this period.