Lecture: Prenatal Development and Birth
Lecture script · about 15–20 minutes spoken · Week 4
Opening
Picture a nursing student on a maternity unit, standing quietly in the corner of a birthing room. A baby arrives. Within a minute, someone on the birth team looks at the baby's breathing, color, and movement, and writes down a small number. A few minutes later, they do it again. Now picture a future preschool teacher who will one day hear a family say, "She came early." Both of them need the same thing from this lecture: a fair way to read the first chapter of a child's story.
Here's where we are. In Week 1 you learned the three domains, the periods of childhood, and the idea that nature and nurture always work together. In Week 2 you met the theories, including the idea of a sensitive period, a time of special readiness. In Week 3 you learned to keep what you observe apart from what it might mean. In this lecture we use all three, because development starts before birth.
I'll take you through six steps. First, the three periods before birth. Then genes and the environment. Then why timing matters for anything that can harm development. Then birth itself. Then the newborn's first score, using the running case. And last, two health definitions you'll hear for the rest of your career. Next week, in Week 5, we follow the same child into the first two years.
1. The three prenatal periods
Start with a house being built. First the lot is chosen and the foundation goes in. Then the frame goes up, and every room, pipe, and wire takes its basic shape. After that come months of finishing work, when the house grows into itself. Hold that picture, because development before birth runs in the same order.
The first stretch is the germinal period. It runs about the first two weeks, from fertilization until implantation, when the fertilized egg attaches itself to the wall of the uterus. That's the foundation going in.
The second stretch is the embryonic period, about weeks 3 to 8. This is the frame going up. It's when the major organs and body structures form. Count those weeks on your fingers, 3 through 8, and you get six of them. Six weeks for the whole basic body plan.
The third stretch is the fetal period, from about week 9 until birth. It's the finishing work: growth and refinement of structures that are already in place. It's the longest of the three, and that length is exactly what fools people.
Notice that I keep saying "about." These week counts are approximate, and sources draw the edges a little differently. They're a map of the usual order, not a stopwatch.
Pause and try this. A friend says, "The fetal period is when the heart and the other major organs form, since it's the longest." What would you tell them?
Think about the house before you answer.
Here's the answer. The major organs form in the embryonic period, about weeks 3 to 8. The fetal period is growth and refinement of what's already built, the way finishing work follows the frame.
Here's a line to keep: germinal settles, embryonic builds, fetal grows.
2. Genes and environment, working together
Picture a family getting ready for a birth. One grandparent is tall, and someone at dinner announces, "This baby's going to be tall. It's in the genes." Is that right? Partly. And "partly" is the whole lesson here.
Two terms in plain words first. A gene is a unit of heredity, an inherited instruction the body uses to build and run itself. A chromosome is a threadlike structure in a cell that holds many genes. In this course we name those structures and stop there.
Now the pair you'll use all course long. Your genotype is your genetic makeup, the set of genes you inherit. Your phenotype is what anyone can observe about you, and it comes from your genotype interacting with the environment. Height is a good example. You can see it and measure it, so it's part of the phenotype. The genotype makes a range of heights possible. Then the environment works on that range, from the uterus to childhood food, sleep, and health. The height a child reaches comes from both.
That's Week 1's nature-and-nurture idea, made concrete. Nature and nurture aren't rivals. They work together, and the uterus is the very first environment any of us lives in.
Pause and try this. Is a person's height part of their genotype or their phenotype, and why?
Say it to yourself in one sentence.
Here's the answer. Height is part of the phenotype, because it's an observable characteristic, and it comes from the genotype interacting with the environment, not from genes alone.
So the dinner-table prediction wasn't wrong, exactly. It named only one of the two inputs.
3. Why timing matters
Imagine an artist sketching an outline in pencil. If water spills on the page in the first minute, the outline is ruined. The same spill on a finished, dry painting does much less harm. One event, two very different results, and the only thing that changed was the timing.
Here's the term. A teratogen is a substance or condition that can harm prenatal development. And its effect depends on three things: the timing, the dose, and the individual. The embryonic period is generally the most sensitive time for the major structures. Why? Go back to Week 2's idea of a sensitive period, a time of special readiness. A structure that's forming is open to help and open to harm. So the window when it forms is the window when a teratogen can do it the most damage.
The course's pinned example is alcohol. I'm going to quote the Centers for Disease Control and Prevention word for word, because this is health guidance and we don't paraphrase it into something softer. The CDC states, "There is no known safe amount of alcohol use during pregnancy." That's the issuing body's statement. It isn't advice from me about any one person, and it never becomes "a little is fine."
The other side of the picture is prenatal care, the regular health care a pregnant person gets from health professionals before the baby is born. We name it in this course and leave questions about any one pregnancy to the professionals.
Now, the sensitive-period idea explains why timing matters. A second theory adds something. Bronfenbrenner's ecological model reminds you that a pregnancy happens inside settings: a family and a clinic, a parent's workplace, a culture's laws and customs. Those settings shape what reaches the baby and what care the family can get.
Pause and try this. Someone says, "A teratogen does the same harm whenever it happens in pregnancy." Which idea from this section answers them?
Give yourself a moment with the painting in mind.
Here's the answer. The sensitive-period idea answers them: a teratogen's effect depends on timing, dose, and the individual, so the same exposure can matter more while a structure is forming. And less sensitive never means safe.
4. Birth and the three stages of labor
Think about moving a big couch out of an apartment. First you open the door wide enough. Then the couch goes through. Then you carry out the last boxes and close up. Birth follows a similar three-part order.
Labor is the process of giving birth, and we describe it in three stages. The first stage is dilation of the cervix: the opening of the uterus gradually widens so the baby can pass through. That's usually the longest stage. The second stage is the birth of the baby. The third stage is the delivery of the placenta, the organ that forms during pregnancy and passes nutrients and oxygen to the developing baby. It comes out after the baby does.
I'm giving you the stages in words and no durations as rules, because every labor is different. One birth's first stage can be much longer or shorter than another's.
Pause and try this. A relative says labor is over the moment the baby is born. Which stage are they forgetting?
Count the stages on your fingers before you answer.
Here's the answer. They're forgetting the third stage, the delivery of the placenta. The baby's arrival is the second stage, and labor isn't finished until the placenta is delivered.
5. The newborn's first score
Back to that birthing room. The birth team needs a fast, shared way to describe how a newborn is doing in the first minutes. A long paragraph would take too long. So they use five quick ratings and add them up.
That's the Apgar score, from Apgar in 1953, in a paper called "A Proposal for a New Method of Evaluation of the Newborn Infant." It rates five signs: heart rate, breathing effort, muscle tone, reflex response, which is sometimes called grimace, and skin color. Each sign gets a 0, a 1, or a 2. The team scores the baby at 1 minute and again at 5 minutes after birth, so each total runs from 0 to 10. MedlinePlus, the National Library of Medicine's health site, states that a score of 7, 8, or 9 is normal, and that a 10 is uncommon.
Now meet the running case, the illustrative child this course follows from birth to 15 years. Record R1 is the newborn. At 1 minute, heart rate got a 2, breathing effort a 2, muscle tone a 1, reflex response a 1, and skin color a 1. Add them: two plus two plus one plus one plus one is 7. At 5 minutes, heart rate 2, breathing 2, muscle tone 2, reflex response 2, and skin color 1. Add them: that's 9.
What changed? Muscle tone went from some bending of the arms and legs to active movement. Reflex response went from a grimace to a cry, a cough, a sneeze, or pulling away. Each rose by one, which is why the total rose from 7 to 9. Skin color stayed at 1 both times: body pink, hands and feet still blue. That's why the baby sits one below the top score of 10.
The record also says the newborn turns toward a touch on the cheek and opens the mouth. Write that in the "what was observed" column and leave the interpretation for Week 5, which names it.
Pause and try this. A relative in the hallway hears "a 7 at one minute" and worries that the baby will struggle in school. What two things would you tell them?
Take a breath and find both.
Here's the answer. First, a 7 is in the normal range; MedlinePlus states that 7, 8, or 9 is normal. Second, the Apgar score describes the newborn's condition in the first minutes, so it predicts nothing about school, intelligence, or later development.
Here's the line I want you to carry: a newborn's score is a snapshot of minutes, not a forecast of years.
6. Low birth weight and preterm birth
Two families leave the same hospital with two different phrases. One heard "born early." The other heard "small at birth." Those sound alike, but they measure two different things, and the World Health Organization defines each one.
Low birth weight is a weight at birth of less than 2,500 grams. That one's about weight. Preterm birth is a baby born alive before 37 completed weeks of pregnancy. That one's about timing. Because they measure different things, a baby can meet one definition, both, or neither. A baby born on time can be small. A baby born early can weigh more than the cutoff.
So you always ask two separate questions. Is the weight under 2,500 grams? Was the birth before 37 completed weeks? Answer each one on its own.
And like the Apgar score, these words describe a birth, not a future. They're reasons for a health team to watch and support a baby, never a verdict anyone in this course draws about a child.
Pause and try this. A classmate uses "preterm" and "low birth weight" as two names for the same thing. What's the difference?
Think weight, then think timing.
Here's the answer. Low birth weight is about weight, less than 2,500 grams, and preterm birth is about timing, before 37 completed weeks. They often appear together, but they're separate definitions.
Closing
Let's pull it together. Development before birth runs in three periods: the germinal period settles, the embryonic period builds the major organs, and the fetal period grows and refines. Your phenotype comes from your genotype working with the environment, so nature and nurture work together from the very first environment, the uterus. A teratogen's effect depends on timing, dose, and the individual, and the CDC states that there is no known safe amount of alcohol use during pregnancy. Labor has three stages: dilation, the birth of the baby, and the delivery of the placenta. The Apgar score totals five signs at 1 and 5 minutes, and record R1's newborn scored 7 and then 9, both normal. And low birth weight is about weight, while preterm birth is about timing.
Next in this module, read the Readings and Resources page, then work through the lecture tutorial, the practice set, and the quiz, and join the discussion. Next week, in Infancy and Toddlerhood: Physical Development, we follow the newborn from record R1 into the first two years of growth, reflexes, and movement.
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