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According to a study conducted by Whitcome, et al., lumbar lordosis can increase from an angle of 32 degrees at 0% fetal mass (i.e. non-pregnant women or very early in pregnancy) to 50 degrees at 100% fetal mass (very late in pregnancy). Postpartum, the angle of the lordosis declines and can reach the angle prior to pregnancy.
Gestational age: 8 weeks and 0 days until 8 weeks and 6 days old. 57–63 days from last menstruation. Embryonic age: Week nr 7. 6 weeks old. 43–49 days from fertilization. The embryo measures 18 mm (3 ⁄ 4 in) in length. Fetal heart tone (the sound of the heart beat) can be heard using doppler. Nipples and hair follicles begin to form.
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 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 earliest fetal response to a sound stimulus has been observed at 16 weeks' gestational age, while the auditory system is fully functional at 25–29 weeks' gestation. [4] At 33–41 weeks' gestation, the fetus is able to distinguish its mother's voice from others.
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The sex of the fetus may be discerned by ultrasound as early as 11 weeks' gestation. The accuracy is relatively imprecise when attempted early. [15] [16] [17] After 13 weeks' gestation, a high accuracy of between 99% and 100% is possible if the fetus does not display intersex external characteristics. [18]
Adapted to the weight of the fetus, this corresponds to 115 mL/min/kg at 20 weeks and 64 mL/min/kg at 40 weeks. [18] It corresponds to 17% of the combined cardiac output of the fetus at 10 weeks, and 33% at 20 weeks of gestation. [18] Endothelin and prostanoids cause vasoconstriction in placental arteries, while nitric oxide causes vasodilation ...