How did you come to be who you are? From beginning as a one-cell structure to your birth, your prenatal development occurred in an orderly and delicate sequence.
There are three stages of prenatal development: germinal, embryonic, and fetal. Let’s take a look at what happens to the developing baby in each of these stages.
Germinal Stage (Weeks 1–2)
In the discussion of biopsychology earlier in the book, you learned about genetics and DNA. DNA is passed on to the child at the moment of conception. Conception occurs when sperm fertilizes an egg and forms a zygote (Figure 9.7). A zygote begins as a one-cell structure that is created when a sperm and egg merge. The genetic makeup and sex of the zygote are set at this point. During the first week after conception, the zygote divides and multiplies, going from a one-cell structure to two cells, then four cells, then eight cells, and so on. This process of cell division is called mitosis. Mitosis is a fragile process, and fewer than one-half of all zygotes survive beyond the first two weeks (Hall, 2004). After 5 days of mitosis there are 100 cells, and after 9 months there are billions of cells. As the cells divide, they become more specialized, forming different organs and body parts. In the germinal stage, the mass of cells has yet to attach itself to the lining of the uterus. Once it does, the next stage begins.
Embryonic Stage (Weeks 3–8)
After the zygote divides for about 7–10 days and has 150 cells, it travels down the fallopian tubes and implants itself in the lining of the uterus. Upon implantation, this multi-cellular organism is called an embryo. Now blood vessels grow, forming the placenta. The placenta is a structure connected to the uterus that provides nourishment and oxygen to the developing embryo via the umbilical cord. Basic structures of the embryo start to develop into areas that will become the head, chest, and abdomen. During the embryonic stage, the heart begins to beat and organs form and begin to function. The neural tube forms along the back of the embryo, developing into the spinal cord and brain.
Fetal Stage (Weeks 9–40)
When the organism is about nine weeks old, the embryo is called a fetus. At this stage, the fetus is about the size of a kidney bean and begins to take on the recognizable form of a human being as the “tail” begins to disappear.
From 9–12 weeks, the sex organs begin to differentiate. At about 16 weeks, the fetus is approximately 4.5 inches long. Fingers and toes are fully developed, and fingerprints are visible. By the time the fetus reaches the sixth month of development (24 weeks), it weighs up to 1.4 pounds. Hearing has developed, so the fetus can respond to sounds. The internal organs, such as the lungs, heart, stomach, and intestines, have formed enough that a fetus born prematurely at this point has a chance to survive outside of the womb. Throughout the fetal stage the brain continues to grow and develop, nearly doubling in size from weeks 16 to 28. Around 36 weeks, the fetus is almost ready for birth. It weighs about 6 pounds and is about 18.5 inches long, and by week 37 all of the fetus’s organ systems are developed enough that it could survive outside the uterus without many of the risks associated with premature birth. The fetus continues to gain weight and grow in length until approximately 40 weeks. By then, the fetus has very little room to move around and birth becomes imminent. The progression through the stages is shown in Figure 9.8.
Link to Learning
For an amazing look at prenatal development and the process of birth, view the video Life’s Greatest Miracle from Nova and PBS.
Prenatal Influences
During each prenatal stage, genetic and environmental factors can affect development. The developing fetus is completely dependent on the person carrying it. Routine prenatal care, which is medical care during pregnancy that monitors the health of both the pregnant person and the fetus (Figure 9.9), is important because it can reduce the risk of complications during pregnancy (NIH, 2013). In fact, people who are trying to become pregnant or who may become pregnant should discuss pregnancy planning with their doctor. They may be advised, for example, to take a vitamin containing folic acid, which helps prevent certain birth defects, or to monitor aspects of their diet or exercise routines. People can face health risks without prenatal care, which is not provided equitably across populations or locations (Backes and Scrimshaw, 2020).
Recall that when the zygote attaches to the wall of the uterus, the placenta is formed. The placenta provides nourishment and oxygen to the fetus. Most everything a pregnant person ingests, including food, liquid, and even medication, travels through the placenta to the fetus, hence the common phrase “eating for two.” Everything in the environment affects the fetus; if they are exposed to something harmful, the child can show life-long effects.
A teratogen is any environmental agent—biological, chemical, or physical—that causes damage to the developing embryo or fetus. There are different types of teratogens. Alcohol and most drugs cross the placenta and affect the fetus. Alcohol is not safe to drink in any amount during pregnancy. Alcohol use during pregnancy has been found to be the leading preventable cause of intellectual disabilities in children in the United States (Maier & West, 2001). Excessive drinking while pregnant can cause fetal alcohol spectrum disorders with life-long consequences for the child ranging in severity from minor to major (Table 9.3). Fetal alcohol spectrum disorders (FASD) are a collection of birth defects associated with heavy consumption of alcohol during pregnancy. Physically, children with FASD may have a small head size and abnormal facial features. Cognitively, these children may have poor judgment, poor impulse control, higher rates of ADHD, learning issues, and lower IQ scores. These developmental problems and delays persist into adulthood (Streissguth et al., 2004). Based on studies conducted on animals, it also has been suggested that alcohol consumption during pregnancy may predispose offspring to like alcohol (Youngentob et al., 2007).
| Facial Feature | Potential Effect of Fetal Alcohol Syndrome |
|---|---|
| Head size | Below-average head circumference |
| Eyes | Smaller than average eye opening, skin folds at corners of eyes |
| Nose | Low nasal bridge, short nose |
| Midface | Smaller than average midface size |
| Lip and philtrum | Thin upper lip, indistinct philtrum |
Smoking is also considered a teratogen because nicotine travels through the placenta to the fetus. When the pregnant person smokes, the developing baby experiences a reduction in blood oxygen levels. According to the Centers for Disease Control and Prevention (2013), smoking while pregnant can result in premature birth, low-birth-weight infants, stillbirth, and sudden infant death syndrome (SIDS).
Heroin, cocaine, methamphetamine, almost all prescription medicines, and most over-the counter medications are also considered teratogens. Babies born with a heroin addiction need heroin just like an adult with a heroin addiction. The child will need to be gradually weaned from the heroin under medical supervision; otherwise, the child could have seizures and die. Other teratogens include radiation, viruses such as HIV and herpes, and rubella (German measles). People who were raised in the United States are much less likely to be afflicted with rubella because most received childhood immunizations or vaccinations that protect the body from disease.
Each organ of the fetus develops during a specific period in the pregnancy, called the critical or sensitive period (Figure 9.8). For example, research with primate models of FASD has demonstrated that the time during which a developing fetus is exposed to alcohol can dramatically affect the appearance of facial characteristics associated with fetal alcohol syndrome. Specifically, this research suggests that alcohol exposure that is limited to day 19 or 20 of gestation can lead to significant facial abnormalities in the offspring (Ashley, Magnuson, Omnell, & Clarren, 1999). Given regions of the brain also show sensitive periods during which they are most susceptible to the teratogenic effects of alcohol (Tran & Kelly, 2003).
What Do You Think?
Should People Who Use Drugs During Pregnancy Be Arrested and Jailed?
As you now know, people who use drugs or alcohol during pregnancy can cause serious lifelong harm to their child. Some have advocated mandatory screenings for pregnant people who have a history of problematic drug use, and if they continue using, to arrest, prosecute, and incarcerate them (Murphy, 2014). For example, in the 1990s South Carolina implemented such a "fetal protection law" called the Interagency Policy on Management of Substance Abuse During Pregnancy, which had disastrous results.
The Interagency Policy applied to patients attending the obstetrics clinic at MUSC, which primarily serves patients who are indigent or on Medicaid. It did not apply to private obstetrical patients. The policy required patient education about the harmful effects of substance abuse during pregnancy. . . . [A] statement also warned patients that protection of unborn and newborn children from the harms of illegal drug abuse could involve the Charleston police, the Solicitor of the Ninth Judicial Court, and the Protective Services Division of the Department of Social Services (DSS). (Jos, Marshall, & Perlmutter, 1995, pp. 120–121)
As with similar laws, this policy seemed to deter pregnant people from seeking prenatal care, deterred them from seeking other social services, and was applied solely to people with low incomes, resulting in lawsuits. The program was canceled after 5 years, during which 42 women were arrested. A federal agency later determined that the program involved human experimentation without the approval and oversight of an institutional review board (IRB). Many states, including Massachussetts, Florida, California, Illinois, and Utah have "mandatory reporting" laws that require healthcare providers to inform child protective services when they suspect that a fetus or infant is exposed to drugs of abuse. Even though prosecutions are rarely pursued in these states, pregnant people still report reluctance to seek care for either their pregnancy or their substance abuse, and make efforts to hide both from providers (Work, 2023). What were the flaws in these programs, and how could states and healthcare providers improve them? What are the ethical implications of charging pregnant people with child abuse?
The content of this course has been taken from the free Psychology textbook by Openstax