When people think about pregnancy, they often focus on the growing baby. However, one of the most remarkable and demanding tasks the body performs during pregnancy is growing an entirely new organ: the placenta.
The placenta is a temporary organ that develops specifically for pregnancy. It serves as the lifeline between mother and baby, delivering oxygen, nutrients, hormones, and immune protection while removing waste products from the developing fetus. Despite its critical role, the placenta often receives little attention outside medical discussions.
Creating and maintaining the placenta requires enormous amounts of energy, nutrients, blood flow, and hormonal coordination. In fact, many of the symptoms women experience during pregnancy, including fatigue, nausea, increased appetite, and physical exhaustion, are partly related to the body’s efforts to build and support this extraordinary organ.
Understanding the physical demands of placental development can help explain why pregnancy is such a significant physiological undertaking, even during the earliest weeks when the baby is still very small.
What Is the Placenta?
The placenta is a specialised organ that develops during pregnancy and attaches to the wall of the uterus.
Through the umbilical cord, it connects the mother’s circulation to the baby’s circulation without the two blood supplies directly mixing.
Main Functions of the Placenta
✔ Delivers oxygen to the baby
✔ Transfers nutrients
✔ Removes waste products
✔ Produces pregnancy hormones
✔ Supports immune function
✔ Helps regulate fetal growth
The placenta is often described as one of the most complex organs the human body can create.
When Does the Placenta Begin to Form?
Placental development begins very early in pregnancy.
Shortly after fertilisation:
- The embryo travels to the uterus.
- Implantation occurs.
- Placental cells begin forming.
- Blood vessel development starts.
Many women are already growing a placenta before they even know they are pregnant.
Early Placental Timeline
| Pregnancy Stage | Placental Development |
|---|---|
| Week 1–2 | Fertilisation and implantation |
| Week 3–4 | Early placental formation |
| Week 5–8 | Rapid growth and blood vessel formation |
| Week 10–12 | Placenta becomes increasingly functional |
| Second trimester | Major nutrient transfer role |
The Placenta Is an Entire Organ
One reason pregnancy is physically demanding is that the body is not simply growing a baby—it is growing a new organ from scratch.
The placenta eventually weighs approximately:
- 450–700 grams at term
It contains:
- Blood vessels
- Connective tissue
- Hormone-producing cells
- Immune-regulating structures
Comparison of Organ Development
| Structure | Development During Pregnancy |
|---|---|
| Baby | Continuous growth |
| Placenta | Entirely new organ formation |
| Uterus | Major enlargement |
| Blood supply | Significant expansion |
Growing an organ requires substantial biological resources.
Why Placental Growth Causes Fatigue
Many women experience overwhelming fatigue during the first trimester.
This often occurs before the baby has grown significantly.
One major reason is placental development.
The body must:
- Produce new blood vessels
- Increase circulation
- Build placental tissue
- Support hormone production
Symptoms Linked to Early Placental Growth
✔ Fatigue
✔ Increased need for sleep
✔ Reduced stamina
✔ Mental exhaustion
✔ Low energy
The body is investing enormous resources into establishing pregnancy.
Increased Blood Volume Requirements
The placenta requires a substantial blood supply.
To meet this demand, maternal blood volume increases by approximately 30–50% during pregnancy.
Why Blood Volume Increases
- Deliver oxygen to the placenta
- Support fetal growth
- Maintain uterine circulation
- Prepare for childbirth blood loss
Effects of Increased Blood Volume
| Adaptation | Purpose |
|---|---|
| Increased plasma volume | Supports circulation |
| Increased cardiac output | Improves blood delivery |
| Expanded vascular network | Feeds placenta |
| Increased oxygen transport | Supports mother and baby |
These changes place additional demands on the cardiovascular system.
The Placenta Produces Hormones
The placenta functions as a powerful endocrine organ.
It produces several essential hormones, including:
- Human chorionic gonadotropin (hCG)
- Progesterone
- Oestrogen
- Human placental lactogen (hPL)
Key Placental Hormones
| Hormone | Function |
|---|---|
| hCG | Supports early pregnancy |
| Progesterone | Maintains uterine lining |
| Oestrogen | Supports fetal and uterine growth |
| hPL | Alters maternal metabolism |
Hormone production requires substantial metabolic activity.
Why Placental Hormones Cause Symptoms
Many common pregnancy symptoms are linked to placental hormone production.
Common Hormone-Related Symptoms
✔ Nausea
✔ Vomiting
✔ Breast tenderness
✔ Fatigue
✔ Food aversions
✔ Mood changes
✔ Increased urination
For example, rising hCG levels are strongly associated with morning sickness.
The Placenta Changes Maternal Metabolism
The placenta does more than transport nutrients—it actively alters how the mother’s body uses energy.
Its goal is to ensure the baby receives adequate nutrition.
This may result in:
- Increased appetite
- Altered insulin sensitivity
- Changes in fat storage
- Increased calorie needs
Metabolic Changes During Pregnancy
| Change | Purpose |
|---|---|
| Increased calorie use | Support growth |
| Fat storage | Energy reserve |
| Insulin resistance | Prioritises fetal nutrition |
| Increased nutrient absorption | Supports placenta and baby |
These adaptations require significant energy from the mother’s body.
Oxygen Demands Increase
As placental and fetal tissues grow, oxygen requirements rise.
The mother’s body responds by:
- Increasing breathing efficiency
- Expanding blood volume
- Enhancing oxygen transport
Effects of Increased Oxygen Demand
✔ Mild breathlessness
✔ Faster heart rate
✔ Increased circulation
✔ Greater energy expenditure
These changes are normal but may contribute to feelings of physical exertion.
Nutritional Demands of Placental Growth
Building and maintaining a placenta requires essential nutrients.
Important Nutrients
| Nutrient | Role |
|---|---|
| Iron | Oxygen transport |
| Protein | Tissue growth |
| Folate | Cell division |
| Calcium | Cellular function |
| Zinc | Placental development |
Deficiencies may affect both maternal wellbeing and placental function.
The Immune System’s Role
Pregnancy presents a unique challenge for the immune system.
The baby carries genetic material from both parents, yet the mother’s body must tolerate the pregnancy rather than reject it.
The placenta helps regulate this process.
Placental Immune Functions
✔ Immune communication
✔ Protection against certain infections
✔ Regulation of maternal immune responses
✔ Support of fetal development
Maintaining this balance requires complex biological coordination.
Why Some Women Feel More Exhausted Than Others
Not every woman experiences placental demands in the same way.
Factors influencing symptoms include:
- Genetics
- Hormonal sensitivity
- Nutritional status
- Multiple pregnancies
- Overall health
Factors Affecting Placental Workload
| Factor | Possible Impact |
|---|---|
| Twins or multiples | Increased demands |
| Anaemia | Greater fatigue |
| Poor nutrition | Reduced energy |
| Sleep deprivation | Increased exhaustion |
Placental Growth and Morning Sickness
Many women wonder why nausea is often worst during the first trimester.
This coincides with:
- Rapid placental growth
- Rising hCG levels
- Hormonal fluctuations
Symptoms Often Linked to Placental Development
✔ Nausea
✔ Vomiting
✔ Food aversions
✔ Heightened smell sensitivity
✔ Fatigue
The timing is not coincidental, placental activity is at its peak during early pregnancy.
When Placental Function Becomes a Medical Concern
Most placentas develop normally, but some complications can occur.
Examples include:
- Placenta previa
- Placental insufficiency
- Placental abruption
- Abnormal implantation
Warning Signs Requiring Medical Assessment
□ Vaginal bleeding
□ Reduced fetal movement
□ Severe abdominal pain
□ High blood pressure
□ Growth concerns
Regular prenatal care helps monitor placental health.
The Placenta After Birth
Once the baby is delivered, the placenta is also delivered.
This stage is known as the third stage of labour.
After birth:
- Placental hormone production stops
- Hormone levels fall rapidly
- Postpartum recovery begins
The body must then adjust to the sudden absence of an organ it has depended on for months.
Normal Pregnancy Fatigue vs Concerning Symptoms
Normal Placenta-Related Fatigue
✔ Improves with rest
✔ Gradual pattern
✔ Common during first trimester
✔ No severe symptoms
Medical Evaluation Recommended
□ Extreme exhaustion
□ Shortness of breath
□ Dizziness
□ Fainting
□ Significant weakness
□ Signs of anaemia
Conclusion
The placenta is one of the most remarkable organs the human body can create. From the earliest weeks of pregnancy, it demands enormous amounts of energy, blood flow, nutrients, and hormonal activity. Many of the symptoms women experience, including fatigue, nausea, appetite changes, and physical exhaustion—are partly the result of the body working tirelessly to build and maintain this essential organ.
Far from being a passive structure, the placenta actively supports fetal growth, regulates hormones, influences metabolism, and helps coordinate immune function throughout pregnancy. Understanding its role helps explain why pregnancy can feel physically demanding even when the baby is still very small.
Recognising the immense work involved in growing a placenta can also encourage greater appreciation for the physiological achievements of pregnancy and the extraordinary adaptations occurring within the maternal body every day.