BIO 004 · Human Anatomy
Pregnancy and Birth
Block 4 · Module 7: Pregnancy and Birth
A reference for the pregnancy and birth video and lab. This page covers fertilization and implantation, the stages of prenatal development, the placenta and fetal membranes, the gravid uterus, and the stages of labor.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the fetal membranes, the gravid uterus, and the stages of labor.
- Describe fertilization and implantation.
- Order the stages of prenatal development from zygote to fetus.
- Name the placenta and the fetal membranes and what each does.
- Describe the gravid uterus and the three stages of labor.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
Fertilization and implantation
Add a labeled diagram from fertilization in the uterine tube to implantation in the endometrium.
The placenta and membranes
Add a labeled view of the fetus, placenta, umbilical cord, and amniotic sac.
The stages of labor
Add a labeled diagram of the dilation, expulsion, and placental stages of labor.
Pregnancy and Birth, an Overview
Pregnancy begins at fertilization and ends at birth. Over those months a single cell becomes a fetus, supported by a temporary set of structures built just for the pregnancy.
- Pregnancythe period from fertilization to birth, during which a fetus develops in the uterus
- Gestationthe length of a pregnancy, about 38 weeks from fertilization, or 40 weeks counted from the last menstrual period
- Embryothe developing offspring during the first 8 weeks after fertilization
- Fetusthe developing offspring from the 9th week until birth
- Trimestersthe three roughly three-month periods that pregnancy is divided into
Fertilization and Implantation
Pregnancy begins when a sperm and an egg unite. The new cell divides as it travels, and about a week later it embeds itself in the wall of the uterus.
- Fertilizationthe union of a sperm and an egg, normally in the ampulla of the uterine tube
- Zygotethe single cell formed at fertilization
- Cleavagethe series of rapid cell divisions the zygote undergoes as it travels toward the uterus
- Morulathe solid ball of cells produced by cleavage
- Blastocystthe hollow ball of cells that reaches the uterus, with an inner cell mass and an outer layer
- Inner cell massthe cluster of cells of the blastocyst that becomes the embryo
- Trophoblastthe outer layer of the blastocyst that becomes the fetal part of the placenta
- Implantationthe embedding of the blastocyst into the endometrium, about a week after fertilization
Stages of Prenatal Development
From one cell to a newborn, development passes through a fixed set of stages. Follow them in order.
- Zygotethe single cell formed when a sperm and an egg unite
- Cleavagerapid cell divisions produce a solid ball of cells, the morula
- Blastocysta hollow ball of cells that reaches the uterus and implants in the endometrium
- Embryofrom implantation through week 8; the organs and body systems form
- Fetusfrom week 9 until birth; the body grows and the systems mature
- Birththe fetus is delivered, ending the gestation
The Placenta and Fetal Membranes
A pregnancy builds temporary structures that support the fetus and are discarded at birth. Compare the placenta and the fetal membranes.
| Structure | What it is | Role |
|---|---|---|
| Placenta | the disc-shaped organ that forms during pregnancy | exchanges oxygen, nutrients, and wastes between the mother's blood and the fetus's blood |
| Umbilical cord | the cord linking the fetus to the placenta | carries the two umbilical arteries and the umbilical vein |
| Amnion | the innermost fetal membrane | forms the fluid-filled sac that surrounds the fetus |
| Amniotic fluid | the fluid within the amnion | cushions the fetus, lets it move, and allows even growth |
| Chorion | the outermost fetal membrane | contributes the fetal portion of the placenta |
| Yolk sac | an early fetal membrane | forms the earliest blood cells and the germ cells |
The Gravid Uterus and Fetal Position
The uterus changes more than any other organ during pregnancy, and the fetus settles into position for birth.
- Gravid uterusthe uterus during pregnancy, which enlarges enormously to hold the growing fetus
- The expanding uterusby full term it reaches up to the rib cage, pushing the abdominal organs aside
- Cervical changesthe cervix stays firm and closed through pregnancy, then softens and thins as birth approaches
- Vertex positionthe head-down position most fetuses settle into by late pregnancy, ready for birth
- Breech positiona position in which the buttocks or feet, rather than the head, are nearest the cervix
- Lighteningthe descent of the fetus lower into the pelvis as birth nears
Labor and Birth
Labor is the process of birth. It is divided into three stages, which follow in a fixed order.
- Dilation stageregular contractions thin and open the cervix until it is fully dilated; the longest stage
- Expulsion stagestrong contractions push the fetus through the cervix and vagina; it ends with the birth of the baby
- Placental stagecontractions continue and expel the placenta, now called the afterbirth
- Laborthe process by which the fetus and placenta are expelled from the uterus
- Afterbirththe placenta and attached membranes, expelled in the placental stage
- Cesarean sectionsurgical delivery of the fetus through an incision in the abdominal and uterine walls
Disorders of Pregnancy
Compare the common conditions of pregnancy by the structure or stage each one affects.
| Condition | Affected structure or stage | What it is |
|---|---|---|
| Ectopic pregnancy | the implantation site | the embryo implants outside the uterus, most often in a uterine tube; a structural emergency |
| Miscarriage | the pregnancy | the loss of a pregnancy before the fetus can survive on its own |
| Placenta previa | the placenta | the placenta lies over the cervical opening and can block the birth canal |
| Preeclampsia | the mother's blood pressure | a serious condition of later pregnancy marked by high blood pressure |
| Gestational diabetes | blood sugar control | high blood sugar that first develops during pregnancy |
| Breech presentation | fetal position | the fetus is positioned buttocks or feet first, which can complicate a vaginal delivery |
See also: The Female Reproductive System for the uterus and ovaries, and Blood Vessel Disorders and Fetal Circulation for the fetal shunts.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Trace the events from fertilization to implantation, naming where each one occurs.
- Name the structures of the placenta and explain what passes between mother and fetus.
- Compare the fetal circulatory shortcuts with the circulation after birth.
- Name the three stages of labor and what happens in each.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.