39.1 Growth and Development Stages

Pre-Embryonic

The pre-embryonic period is also known as the germinal period. This pre-embryonic period occurs in the first two weeks after conception. In the early pre-embryonic period, days one to three after conception, the fertilized egg, or zygote, remains in the fallopian tube. By the third day, the zygote has replicated to be approximately sixteen cells. This mass of cells is called the morula, and it migrates from the fallopian tube to the uterus for implantation. In the uterus, the mass of cells continues to grow and forms a blastocyst and a trophoblast. The blastocyst is the cluster of cells that ultimately develops into the embryo; it is surrounded by the trophoblast, which is the group of cells that develops into the placenta. By the end of this period, the fertilized egg is implanted in the uterus (Lally & Valentine-French, 2019).

Embryonic

The embryonic period is the period of development from approximately two weeks after conception to eight weeks after conception. During this stage, the blastocyst and trophoblast that developed in the pre-embryonic stage continue to specialize. The trophoblasts develop chorionic villi, or a network of blood vessels that penetrate the lining of the uterus. The blood vessels from the lining of the uterus dilatate and grow around the chorionic villi, ultimately becoming the placenta.

The other cellular formation from the pre-embryonic phase, the blastocyst, develops into three cell layers: the ectoderm, the mesoderm, and the endoderm. These three layers develop into all the tissue and organ systems in the human body. The ectoderm becomes the outer layer of skin, hair, nails, and mucous membranes. The mesoderm becomes the deeper skin layers, cartilage, bones, muscles, cardiac structures, and kidneys. The endoderm becomes the lining of the trachea, pharynx, bronchi, and gastrointestinal (GI) and genitourinary (GU) tracts.

A key concept of embryonic development is that if there is a problem in a cell layer it will likely affect multiple organ systems. For example, both the cartilage, a key component of ear formation, and the kidneys develop from the mesoderm layer. It is common that children born with congenital kidney problems also have problems with their ears (Phelan & Rheault, 2018).

It is also important to remember that the risk of teratogenic exposure is highest during the embryonic developmental stage. A teratogen is any external force, like a medication, chemical, alcohol, drug, or maternal infection, that can cause fetal abnormalities. Since the basic structure of the human body is being developed in this stage, exposure to teratogen has the potential to cause permanent damage or even death (Lally & Valentine-French, 2019).

Fetal

The fetal period describes prenatal development from week nine after conception to birth (see Figure 39.3). By week nine, all the organ systems and external structure of an infant are partially developed. From this point forward, the organ systems continue to mature and prepare the fetus for extrauterine life. There are several key developmental milestones of the fetal developmental stage. By sixteen weeks’ gestation, the gender can be determined. At twenty-four weeks, fetal breathing movements start to occur. Around twenty-eight weeks, the fetus begins to develop surfactant, which is a hormone needed to keep the alveoli in the lungs open. Around thirty-two weeks, the fetus begins to demonstrate the sucking reflex, which is a survival reflex needed to feed. Forty weeks is considered full term (Lally & Valentine-French, 2019).

Figure 39.3 During the fetal stage, the baby’s brain develops, and the body adds size and weight until the fetus reaches full-term development. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Physical

Full-term newborns are born with reflexes that are protective in nature. For example, they have a rooting reflex and a suck reflex. The rooting reflex is an innate response to stimulation of the face, mouth, or cheek. It helps babies find and latch onto a nipple to begin feeding. The suck reflex begins around thirty-two weeks’ gestation and is an automatic response to suck and swallow in response to oral stimulation (Saddleback College, 2019).

A healthy newborn is expected to lose 7 to 10 percent of their birth weight in the first two to three days after birth. This is because newborns are born with excess fluid as a result of the birthing process, especially if the birthing person received intravenous fluid during labor (Miyoshi et al., 2020). They should regain their birth weight by the first two weeks. Once they regain their birth weight, newborns should gain an average of 1 oz (30 g) per day and grow 1 to 1.5 in. (2.5 to 4 cm) over the first twenty-eight days (Desiraju, 2018).

Behavioral

The most important psychosocial milestone of the neonatal period is bonding with the caregiver and developing a sense of trust. It is important to educate parents about normal neonatal sleeping and feeding behavior so they can respond appropriately to their infant.

Neonates sleep for approximately twelve to sixteen hours per day. When they are not sleeping, they are most often feeding. It is common for a bottle-fed neonate to feed every two to three hours. Breastfed neonates may feed more frequently, every one and a half to two hours.

During these initial twenty-eight days, it is extremely important that parents learn to recognize cues from their infant. As parents respond when the infant is hungry, has a dirty diaper, or is uncomfortable, the neonate develops a sense of trust, which is an important element of psychosocial and personality development throughout childhood.

Physical

Rapid growth is the hallmark feature of infancy. By 6 months of age, infants are expected to double their birth weight, and they should triple their birth weight by 1 year. They should also be growing between ½ and 1 in. (1.3 and 2.5 cm) every month.

In addition to rapid changes in height and weight, infants’ heads are also growing during this age range. At birth, an infant’s head circumference, on average, is ¾ in. (2 cm) greater than the chest circumference. The head continues to grow rapidly during the first four months and then starts to slow down. By approximately 6 months of age, the head circumference and the chest circumference are equal (Graber, 2023).

Developmental Patterns

Infant development patterns revolve around acquisition of gross motor skills. There are two primary developmental patterns: proximodistal and cephalocaudal. In the proximodistal pattern, development occurs closer to the midline first and then in extremities. For example, infants have trunk control, which is midline, before they have control of their hands and feet, which are distal. In the cephalocaudal pattern, development begins first with the head and then extends downward toward the trunk. An example of cephalocaudal development is having head and neck control before having control of the trunk and extremities.

Cognitive

Cognitive development in infancy is assessed by evaluating whether the infant is meeting developmental milestones. Developmental milestones are activities 75 percent or more of children can do by a certain age (Table 39.1) (Centers for Disease Control and Prevention, 2023).

Psychosocial

The psychosocial development of an infant 1 month to 1 year focuses on recognition of caregivers and the initiation of play. By approximately 6 months of age, infants demonstrate separation anxiety, or fear of abandonment when their primary caregiver leaves. This behavior is a normal part of development that children usually outgrow by age 3 years.

Throughout the first year, infants become more active with their play. Starting at 6 months, infants enjoy knocking over blocks, rolling a ball on the floor, and playing with other sensory toys. They learn to explore their environment through play and develop both their fine and gross motor skills. Providing a safe environment for infants to play is an important part of caring for them (Newton, 2022).

Physical

Although physical growth slows during the toddler years, toddlers noticeably change year by year in their physical size. By approximately age 2 years, toddlers have quadrupled their birth weight. Once this milestone is achieved, they continue to gain 4 to 6 lb (2 to 3 kg) per year and grow 2 to 3 in. (5 to 7.5 cm). This rate of growth continues to approximately age 3 years (Graber, 2023).

Cognitive

Toddlers are on the go. They love running, climbing, and testing out their new physical skills. Much of toddlers’ cognitive development is demonstrated in their rapid achievement in gross motor skills. By the end of the toddler years, children should be able to throw a ball, kick a ball, and run without falling (Saddleback College, 2019).

In addition to rapid attainment of new gross motor skills, toddlers develop language skills and fine motor skills. By the end of the second year, children should be able to speak in two- to three-word sentences and have a 200-word vocabulary. They should also have the fine motor skills needed to scribble with a crayon or marker and be able to feed themselves with a spoon and fork (Byington & Kim, 2015).

Psychosocial

The primary psychosocial achievement during the toddler years is to transition from independent play to parallel play. Children learn how to socialize through play. During parallel play, children play near each other but not with each other. Although it appears that children engaged in parallel play are not paying attention to the other child, they are. They often mimic the other child and are learning to socialize (Figure 39.5). This type of play is a bridge to other more advanced play that develops throughout childhood (Newton, 2022).

Figure 39.5 Children may engage in parallel play even when they are in close proximity, and may switch between playing together or separately at any time. (credit: US Army Southern European Task Force/Flickr, CC-BY 2.0)

Physical

The rate of growth continues to slow during the preschool years. The average preschool-age child gains 5 lb (2 kg) per year and grows 3 in. (8 cm) per year. As their body proportions change, they become more coordinated with their movements. Their limbs grow longer, and their balance improves, making it easier for them to participate in active play. In addition to these changes, their abdominal muscles strengthen so their abdomen no longer looks distended, and they have a more slender physique (Graber, 2023).

Cognitive

Cognitive development in the preschool years focuses on changes in how children think. Toddlers are very egocentric and view the world only from their perspective. Preschool-age children have a greater appreciation of others and are very creative. Their language skills are growing exponentially, and they love to tell stories. They also frequently have imaginary friends and like to play make believe.

By the end of this developmental stage, children should have the cognitive skills to learn new knowledge. Attending preschool helps them get ready. Children who attend preschool are likely able to write their name, cut with scissors, and draw shapes when they start school. They are also used to being in a group setting and can follow rules. All of this makes it easier for them to adapt to the school environment (Newton, 2022).

Psychosocial

Psychosocial development in preschool children revolves around learning to function outside of the home, being away from their primary caregiver, and learning the rules of being in a group setting.

A common stress for parents of preschool-age children is separation anxiety. Children in this age group frequently have a hard time adjusting when they are left at preschool. It is important to teach parents that separation anxiety is a normal part of development and does not mean that their child is not ready for preschool (National Health Services UK, 2023).

Physical

Growth continues at a steady pace during the school-age years. On average, children grow 2.5 in. (6 cm) per year and gain 5 to 7 lb (2 to 3 kg) per year. By the end of the school-age period, children start to accumulate more fat in preparation for the growth spurt that occurs during adolescence. Another important physical change of this period is related to teeth. Around age 6 years, children start to lose their deciduous teeth. By age 12 to 13 years, all their adult teeth, except their wisdom teeth, should be in (Graber, 2023).

Cognitive

As children mature through the school-age period, their ability to pay attention and concentrate increases. They move beyond learning through memorization to developing math skills, writing skills, and problem-solving skills. Their language evolves, and they can understand grammar rules, participate in creative writing activities, and use language in a more expressive way (Saddleback College, 2019).

Psychosocial

Peer-to-peer relationships are the backbone of psychosocial development for school-age children (Ţepordei et al., 2023). In this age group, children tend to have a best friend, and friendship groups start to form. Children like to spend time with their friends through activities like riding bicycles, skating, swimming, and participating in competitive sports (Figure 39.6). Although they are still very active, their fine motor skills have developed to the point that they can sit and work on projects. They frequently enjoy drawing, computer work, and hobbies like collecting things (Newton, 2022).

Figure 39.6 Because they understand luck and fairness, children in middle and late childhood (6 to 11 years old) are able to follow rules for games. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Physical

The primary physical change during adolescence is puberty, or the development process of becoming sexually mature. Puberty is a stepwise process that takes about five years. People assigned female at birth tend to enter puberty before people assigned male. The onset of puberty for females is usually between the ages of 8 and 13 years. Males tend to start puberty between the ages of 9 and 14 years (National Institutes of Health, 2021).

In addition to sexual maturation, all people go through a rapid growth spurt during adolescence. They tend to grow between 3 and 3.5 in. (7.5 and 9 cm) per year during their peak growth spurt. However, females tend to stop growing sooner. Most females reach their final, adult height two years after menarche (first menstrual period), while males tend to continue growing until age 20 years (Graber, 2023).

Cognitive

Cognitive maturation during adolescence focuses on two elements: abstract thinking and a sense of morality. By the end of adolescence, teenagers should have developed abstract thinking, or the ability to think through scenarios with different possible outcomes and evaluate which outcome would be best. The same process is true with regard to a sense of right versus wrong. Prior to adolescence, children view ethical dilemmas based on the desire to follow rules or to avoid punishment. By the end of adolescence, they can analyze individual circumstances and make decisions based on a sense of ethical correctness (Figure 39.7) (Newton, 2022).

Figure 39.7 Teenage thinking is characterized by the ability to reason logically and solve hypothetical problems such as how to design, plan, and build a structure. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Psychosocial

The primary psychosocial task of adolescence is establishing independence and an identity apart from the family of origin. Peer relationships are incredibly important in this age group (Figure 39.8). Adolescents dress like their friends, participate in the same activities as their friends, and are prone to give in to peer pressure. This can be a challenging time for parents. As adolescents try to assert their autonomy, they challenge the authority of their parents. This process is made even more tumultuous by the hormonal changes of puberty that can lead to emotional outbursts (Saddleback College, 2019).

Figure 39.8 Peers are a primary influence on our development in adolescence. (credit: “130726-F-BZ180-001” by Staff Sgt. Luther Mitchell/U.S. Air Force, Public Domain)