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By about week 21, the fetus begins to develop a regular schedule of movement. [17] The startle reflex is present in half of all fetuses by week 24 and in all fetuses by week 28. [19] Movement is restricted around this time because the fetus has grown so large it has little space for kicking or changing body position. [20]
Quickening indicates the start of fetal movements, usually felt 14–26 weeks after conception, or between the fourth and sixth month. [ 5 ] [ 6 ] A woman pregnant for the first time (i.e., a primigravida woman) typically feels fetal movements at about 20–21 weeks, whereas a woman who has given birth at least once will typically feel ...
A baby's chances for survival increases 3 to 4 percentage points per day between 23 and 24 weeks of gestation, and about 2 to 3 percentage points per day between 24 and 26 weeks of gestation. After 26 weeks the rate of survival increases at a much slower rate because survival is high already. [16]
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. Location of the elbows and toes are visible. Spontaneous limb movements may be detected by ultrasound.
The fetus is considered full-term between weeks 37 and 40 when it is sufficiently developed for life outside the uterus. [14] [15] It may be 48 to 53 cm (19 to 21 in) in length when born. Control of movement is limited at birth, and purposeful voluntary movements continue to develop until puberty. [16] [17]
Synapses do not begin to form until week 17. [11] Neural connections between the sensory cortex and thalamus develop as early as 24 weeks' gestational age, but the first evidence of their function does not occur until around 30 weeks, when minimal consciousness, dreaming, and the ability to feel pain emerges. [12]
One randomized controlled trial, however, came to the result of a higher perinatal death rate of normally formed infants born after 24 weeks exposed to Doppler ultrasonography (RR 3.95, 95% CI 1.32–11.77), but this was not a primary outcome of the study, and has been speculated to be due to chance rather than a harmful effect of Doppler itself.
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.