This article dr spock baby and child care pdf about the stage of prenatal development. Views of a Foetus in the Womb detail.
In biological terms, however, prenatal development is a continuum, with no clear defining feature distinguishing an embryo from a fetus. Canada and the United States. English spelling throughout the world in medical journals. In humans, the fetal stage commences at the beginning of the ninth week. The head makes up nearly half of the fetus’ size.
Breathing-like movement of the fetus is necessary for 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. The genitalia of the fetus starts to form and placenta becomes fully functional during week 9. At this point in development, uncontrolled movements and twitches occur as muscles, the brain, and pathways begin to develop. The amount of body fat rapidly increases. Lungs are not fully mature. Bones are fully developed, but are still soft and pliable.
Fingernails reach the end of the fingertips. 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. Control of movement is limited at birth, and purposeful voluntary movements develop all the way until puberty. There is much variation in the growth of the human fetus.
Also, female fetuses tend to weigh less than males, at full term. SGA may be associated with growth delay, or it may instead be associated with absolute stunting of growth. Weeks and months numbered by gestation. Viability refers to a point in fetal development at which the fetus may survive outside the womb.
There is no sharp limit of development, age, or weight at which a fetus automatically becomes viable. It is rare for a baby weighing less than 1. If given expert postnatal care, some fetuses weighing less than 1. 30 percent of neonatal deaths.
According to the conclusions of a review published in 2005, “Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester. Nevertheless, the perception of pain involves sensory, emotional and cognitive factors and it is “impossible to know” when pain is experienced, even if it is known when thalamocortical connections are established. A functional circulatory system is a biological necessity, since mammalian tissues can not grow more than a few cell layers thick without an active blood supply. The prenatal circulation of blood is different than the postnatal circulation, mainly because the lungs are not in use. With the first breath after birth, the system changes suddenly. Remnants of the fetal circulation can be found in the adult. This enables fetal hemoglobin to absorb oxygen from adult hemoglobin in the placenta, where the oxygen pressure is lower than at the lungs.