These genetic factors influence the rate at which alcohol and its initial metabolic product, acetaldehyde, are metabolized. They are found at different frequencies in people from different parts of the world. The alcohol dehydrogenase allele ADH1B*2 causes a more rapid metabolism of alcohol to acetaldehyde, and reduces risk for alcoholism; it is most common in individuals from East Asia and the Middle East. The alcohol dehydrogenase allele ADH1B*3 also causes a more rapid metabolism of alcohol. The allele ADH1B*3 is only found in some individuals of African descent and certain Native American tribes. African Americans and Native Americans with this allele have a reduced risk of developing alcoholism. Native Americans, however, have a significantly higher rate of alcoholism than average; risk factors such as cultural environmental effects (e.g. trauma) have been proposed to explain the higher rates. The aldehyde dehydrogenase allele ALDH2*2 greatly reduces the rate at which acetaldehyde, the initial product of alcohol metabolism, is removed by conversion to acetate; it greatly reduces the risk for alcoholism.A genome-wide association study (GWAS) of more than 100,000 human individuals identified variants of the gene KLB, which encodes the transmembrane protein β-Klotho, as highly associated with alcohol consumption. The protein β-Klotho is an essential element in cell surface receptors for hormones involved in modulation of appetites for simple sugars and alcohol. Several large GWAS have found differences in the genetics of alcohol consumption and alcohol dependence, although the two are to some degree related.
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.