In humans, the fetal stage starts nine weeks after fertilization.  At the start of the fetal stage, the fetus is typically about 30 millimetres (1+¹⁄₄ in) in length from crown-rump, and weighs about 8 grams. The head makes up nearly half of the size of the fetus. Breathing-like movements of the fetus are necessary for the stimulation of lung development, rather than for obtaining oxygen. The heart, hands, feet, brain and other organs are present, but are only at the beginning of development and have minimal operation.

At this point in development, uncontrolled movements and twitches occur as muscles, the brain, and pathways begin to develop.

Weeks 17 to 25 (3.6 to 6.6 months)

A woman pregnant for the first time (nulliparous) typically feels fetal movements at about 21 weeks, whereas a woman who has given birth before will typically feel movements by 20 weeks. By the end of the fifth month, the fetus is about 20 cm (8 in) long.

Weeks 26 to 38 (6.6 to 8.6 months)

The amount of body fat rapidly increases. Lungs are not fully mature. 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. Bones are fully developed, but are still soft and pliable. Iron, calcium, and phosphorus become more abundant. Fingernails reach the end of the fingertips. The lanugo, or fine hair, begins to disappear, until it is gone except on the upper arms and shoulders. Small breast buds are present on both sexes. Head hair becomes coarse and thicker. Birth is imminent and occurs around the 38th week after fertilization. The fetus is considered full-term between weeks 36 and 40, when it is sufficiently developed for life outside the uterus. 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.

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Regards,
Andrina Williams
Managing Editor