Child Development From Infancy to Adolescence. Laura E. Levine

      Figure 4.2 Development of the blastocyst.

      Source: Jim Dowdalls/Photo Researchers, Inc.

      Cells in the trophoblast secrete an enzyme that digests some of the lining in the uterus so that the blastocyst can securely embed itself there. After implantation, fingerlike extensions from the trophoblast grow into the uterus, and a connection between the embryo and the woman is established (Butkus, 2015). Once an outside source of nourishment is available, the blastocyst can really begin to increase in size.

      Couples who engage in frequent, unprotected sex can expect to conceive a child within 1 year, so when this does not happen it may mean that the couple is dealing with infertility. About 12% of married women in the United States have difficulty either getting pregnant or carrying a pregnancy to term (RESOLVE: The National Fertility Association, 2017). One third of the cases are attributable to female factors and one third to male factors; in the remaining cases the cause is mutual or cannot be determined (RESOLVE, 2017). Although infertility can be the result of physical problems in either partner, one of the most significant factors is maternal age. Women in the United States are waiting longer to have children, and today 20% don’t have their first child until they are 35 or older (Centers for Disease Control and Prevention [CDC], 2017l). About one third of these women will have a problem with fertility, but medical science today can offer infertile couples a wide range of interventions. Several are described in Table 4.1.

      Infertility: The inability to conceive within 1 year of frequent unprotected sex.

       Table 4.1

      Sources: American Pregnancy Association (2017); CDC (2017l).

      T/F #2

      Using techniques that are available today, it is possible for some parents to choose the sex of their baby with 100% accuracy. True

      The term assisted reproductive technology (or ART) describes all procedures in which both the egg and the sperm are handled outside of the body (CDC, 2017l). It does not include procedures that involve only the sperm, such as artificial insemination, or in which the woman receives medication intended to stimulate egg production. By this definition, 1.6% of infants born in the United States in 2014 were conceived using ART (Sunderam et al., 2017).

      Despite the emotional toll of infertility, less than one third of infertile couples seek counseling, but when they do, it is important that they receive the specific type of support that they need (Read et al., 2014). For one couple, that might be emotional support to help them deal with what they see as an unforeseen and uncontrollable event in their lives, for another it might be information about the options they have, and another couple may need both types of help.

      The Embryonic Stage (2 Weeks to 2 Months)

      The embryonic stage begins at about 2 weeks postconception and lasts until 8 weeks. At this point, the conception is called an embryo. The embryo is surrounded by a support system that connects it to the mother. This support system includes two membranes as well as the placenta and umbilical cord. You can think of the membranes as two sacs, one inside the other. The chorion is the outer one, and the connection that it establishes with the uterus gives rise to the placenta. The inner one, called the amnion, surrounds the developing embryo and is filled with amniotic fluid to cushion and protect the embryo (later called the fetus). The placenta performs the essential functions of bringing oxygen and nutrients from the mother to the developing organism throughout the pregnancy through the umbilical cord. Later in the pregnancy, it also will carry away fetal waste products. Both functions are described in more detail in the next section.

      Embryonic stage: The prenatal stage that lasts from 2 weeks to 2 months postconception.

      Placenta: The organ that supports a pregnancy by bringing oxygen and nutrients to the embryo from the mother through the umbilical cord and carrying away fetal waste products.

      During the embryonic stage, all the major organ systems of the body are laid down in a process called organogenesis, meaning the genesis or beginning of the organs. The inner cell mass differentiates into three layers, each of which goes on to become different organs and structures, as shown in Figure 4.3. The outermost layer, the ectoderm (ecto means “outside” or “external”), becomes the skin, the sense organs, and the brain and spinal cord. The innermost layer, the endoderm (endo means “within” or “inner”), goes on to become the respiratory system, the digestive system, the liver, and the pancreas. The layer between these two other layers, the mesoderm (meso means “middle”), becomes the muscles, bones, blood, heart, kidneys, and gonads.

      Organogenesis: The process in prenatal development by which all of the major organ systems of the body are laid down.

      Description

      Figure 4.3 Differentiation of the inner cell mass.

      Source: DevelopmentalBiology.net (n.d.). Ectoderm, mesoderm, endoderm. Retrieved from http://www.developmentalbiology.net/images/neurulasm.jpg

      At 4 weeks, a primitive heart begins beating, and at about 5 to 6 weeks, spontaneous movement begins, although the mother cannot yet feel this movement. By 8 weeks, all the major organs and structures of the body have been laid down and the brain and nervous system are developing rapidly, although the organs will need quite a bit more time before they are able to do the work they are intended to do. Anything in the prenatal environment that disrupts the process at this point can cause damage that is both severe and irreversible. Unfortunately, at this point the woman may not even realize she is pregnant which is why women of childbearing age are urged to be cautious about decisions they make that could affect the health of a pregnancy even if they do not think they are pregnant.

      During the prenatal period, development moves from the head region down through the body. This is called cephalocaudal development (cephalus means “head,” and caudal means “tail”). Consequently, throughout the pregnancy, but especially in the early months, the development of the upper half of the embryo (and later of the fetus) is more advanced than the lower half.

      Cephalocaudal development: A principle whereby development proceeds from the head region down through the body.