The placenta is one of the most remarkable organs in nature. It transfers everything your baby needs — oxygen, glucose, amino acids, fatty acids, vitamins, and antibodies — from your bloodstream to your baby's, without your blood and your baby's blood ever mixing.
How Exchange Happens
Your blood flows through the intervillous space around placental villi. Fetal blood flows inside the villi through tiny capillaries. The exchange membrane separating them is extremely thin — in some places, just a single cell layer. Substances pass across by diffusion, facilitated transport, or active transport.
What Gets Transferred and How
| Substance | Transfer Mechanism | Key Fact |
|---|---|---|
| Oxygen | Simple diffusion | Higher concentration in maternal blood drives passive flow to baby |
| Carbon dioxide | Simple diffusion | Moves from baby's blood to mother's for exhalation |
| Glucose | Facilitated diffusion (GLUT transporters) | Largest single energy source for the fetus |
| Amino acids | Active transport | Moved against concentration gradient — baby has more |
| Fatty acids | Facilitated diffusion | DHA critical for brain development |
| IgG antibodies | Active receptor-mediated transport | Surge in final 4 weeks |
| Iron | Active transport | Baby gets iron priority — maternal stores deplete first |
When the Placenta Underperforms
Placental insufficiency means the placenta cannot deliver adequate oxygen and nutrients to the baby. Signs include poor fetal growth on scan, reduced amniotic fluid, and abnormal Doppler blood flow readings. Causes include pre-eclampsia, maternal smoking, autoimmune conditions, and umbilical cord problems.
What You Can Do to Support Placental Function
- Eat iron-rich foods (lean meat, legumes, fortified cereals)
- Include DHA sources (oily fish, DHA-enriched eggs, omega-3 supplements)
- Do not smoke — smoking constricts placental blood vessels directly
- Control blood pressure and blood sugar through diet and exercise
- Attend all scheduled scans so growth problems are caught early
Tip
Iron is often the first nutrient to be depleted in pregnancy. If you feel exhausted in the second trimester, ask your doctor to check your ferritin level.