Child Development From Infancy to Adolescence. Laura E. Levine
womb. If the test is repeated at about 20 weeks, it can confirm that the fetus is continuing to grow at the expected rate and the physician can check for any physical abnormalities, confirm if there is more than one fetus, determine whether other aspects of the pregnancy appear to be normal, and visually determine the sex of the baby. Because this is a medical procedure, the American Congress of Obstetricians and Gynecologists (ACOG, 2017b) recommends that ultrasounds be performed only when there is a medical reason for them, so women with low-risk pregnancies may not have this test at all.
Ultrasound: A prenatal test that uses high-frequency sound waves to create an image of the developing embryo’s size, shape, and position in the womb.
Prenatal testing. This technician is performing a prenatal ultrasound for this couple. A standard ultrasound produces the top image, but the 3-D ultrasound image at the bottom can show some birth defects that would not be apparent on a standard ultrasound. Both of these images are of a normally developing fetus.
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BSIP / Contributor via Getty Images
BSIP / Contributor via Getty Images
The Fetal Stage (2 Months to Birth)
From the beginning of the third month postconception until the baby is born is the fetal stage. This stage is characterized by a remarkable increase in size and weight of the fetus as all the organ systems complete their development and become functional so the newborn can survive independently of the mother after birth.
Fetal stage: The prenatal stage that lasts from week 9 postconception to birth.
Fetus: The developing organism from the end of the eighth week postconception until birth.
We said earlier that the placenta provides oxygen and nutrients to the developing organism and carries away metabolic waste products. Figure 4.4 shows how this occurs. Arteries from the fetus enter spaces in the placenta that are filled with maternal blood, spiral around within these spaces, and then return as a closed loop to the fetus. Because the concentration of oxygen and nutrients is high in the maternal blood and low in the fetal blood, these substances move from the mother’s blood through the artery walls and are carried back to the fetus. In a similar way, the waste products that are in high concentration in the fetal blood move into the spaces in the placenta, where the maternal blood picks them up to transport back to the mother for disposal through her organ systems. At no point do fetal and maternal arteries or veins directly connect (Cunningham, Leveno, et al., 2014). Each blood supply remains separate throughout the pregnancy. This is why a mother and her child can have different blood types.
Figure 4.4 Functions of the placenta.
Source: Anatomy & Physiology, Connexions Website.
One particularly significant event during this period is the transformation of the genitalia of the fetus into male or female genitalia. Although the biological sex of the embryo is determined at conception by the chromosomal information carried in the sperm, until this point in the pregnancy the appearance of male and female embryos has been the same (McClure & Fitch, 2005). At 9 weeks of age, the testes in a male fetus begin to produce the male hormone androgen, and that hormone alters the development of the genitalia from this point on. In a female fetus, in the absence of androgen, the genitalia continue along their developmental pathway, and a female reproductive system is laid down.
Hormones produced prenatally not only shape the physical development of the fetus, but also influence the development of the brain (McCarthy, 2015). For example, there are prenatal differences in the amygdala, the area of the brain that processes emotion and certain social behaviors such as rough-and-tumble play in children, and also in the preoptic area that is implicated in male sexual behavior (McCarthy, 2015). However, when we talk about such differences, it is important to remember that there are many more similarities than differences between male and female brains, and many other factors, such as experiences later in life, also affect the formation of boys’ and girls’ brains.
At about 10 weeks, fetal breathing movements begin. Although there is no air in the amniotic sac to breathe, fetuses breathe in and then expel amniotic fluid. Between week 18 and week 25, most women will begin to feel the movement of the fetus. At first this feels like a light fluttering, but as time goes on, the movement becomes more and more marked. The developing fetus also has periods of wakefulness and periods of sleep, much of which is REM sleep that is marked by rapid eye movements. While adults spend 20% to 25% of their sleep in a REM state, fetuses spend about 90% in REM sleep. Sleep scientists believe that this amount of REM sleep is necessary for prenatal neural development (McNamara, 2012).
Although the fetus is protected from extreme stimulation within its uterine environment, it is not isolated from the sensory world. The “skin senses” such as touch and pain and the proprioceptive senses that detect motion or the position of the body are the first to develop prenatally. These are followed by the chemical senses, such as smell and taste, and the vestibular senses, such as the sense of equilibrium and balance. The last to develop are the auditory and visual senses (Lecanuet, Graniere-Deferre, & DeCasper, 2005).
The intrauterine environment provides at least some stimulation for all these senses and by the time the baby is born, all are functional to some extent (Hopkins & Johnson, 2005). For instance, sounds that are transmitted through the mother’s abdomen provide auditory stimulation (Thurston, 2008), amniotic fluid carries chemosensory molecules that stimulate the smell and taste receptors, and movement of the fetus stimulates the vestibular senses (Lecanuet et al., 2005). Throughout the prenatal period we see a great deal of continuity as systems develop and later become functional. This prepares the newborn to begin interacting with—and responding to—the environment almost immediately after birth.
There is even evidence that some simple forms of learning can occur before birth. Research has found that newborns respond differently to vowel sounds that were part of the native language they were exposed to in utero than to sounds they did not hear prenatally (Moon, Lagercrantz, & Kuhl, 2013). This is an indication of an intact and functional central nervous system, but researchers caution that we should not presume that differences in prenatal stimulation are related to later differences in cognitive functioning (Lecanuet et al., 2005). Research on prenatal sensory capabilities has led to the development and marketing of some gadgets that purport to stimulate neural growth or to facilitate learning, memory, thinking, and even social interaction prenatally. However, this shows a lack of understanding of the meaning of the research. Stimulation beyond what is normally provided to the developing fetus is not necessarily better and could, in fact, be harmful (Krueger, Horesh, & Crosland, 2012). The normal prenatal environment provides enough stimulation for optimal development.
Unnecessary prenatal stimulation. Although there are commercial devices that claim to provide extra beneficial stimulation to the developing fetus while in utero, there is no scientific support for this practice. Everyday sounds in the mother’s environment provide all the stimulation that is necessary.
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