The Incredible Changes Your Body Makes During Pregnancy

Pregnancy is such a beautiful and transformative time. While every woman’s experience is unique, one thing is universal: your body is doing absolutely incredible things to support new life.

Sometimes these changes feel exciting, sometimes uncomfortable, and often a little confusing. My goal is to walk you through what’s happening inside your body so you can better understand (and appreciate!) the amazing adaptations you’re making to grow your baby.

Let’s dive in.

Cardiovascular System: Your Heart Works Overtime

Your heart and blood vessels go through big shifts during pregnancy:

• Blood volume increases significantly.

• Resting heart rate rises by about 15–20 beats per minute.

• Cardiac output (the amount of blood pumped) increases 30–50%.

This makes sense—you’re now circulating blood, oxygen, and nutrients for two.

Other changes include:

• Blood pressure: The bottom number (diastolic) often drops until about week 28.

• Heart position: The heart shifts upward and slightly forward to make space for baby.

• Blood flow: Increases to the uterus, kidneys, and skin to nourish baby, filter waste, and regulate mom’s temperature.

💡 A note about lying on your back: After about 16 weeks, lying flat can compress the large vein that helps blood return from your legs to your heart. That’s why side-sleeping is recommended. But if you wake up on your back—don’t panic. Just roll over and get comfy with some pillows for support.

During exercise, short periods lying on your back are typically safe as long as you feel good (no numbness, tingling, or dizziness). It’s prolonged time on your back we want to avoid.

Respiratory System: Why You Feel Out of Breath

Many women notice breathing feels different in pregnancy, and here’s why:

• Swelling (edema) in the upper airways makes breathing feel harder.

• Hormones (like progesterone and relaxin) loosen ligaments around your ribcage.

• Oxygen needs increase by 30% to supply both you and baby.

• The diaphragm (your main breathing muscle) rises by about 4 cm as baby grows, limiting deep breaths.

• Ribcage changes: The angle of your ribs expands (from ~68° to ~103°), creating more room for baby.

So, that feeling of shortness of breath? Totally normal. Your body is just adjusting to its new demands.

Endocrine System: Hormones on Overdrive

Pregnancy is a hormonal symphony, and a lot is happening behind the scenes:

• Pituitary gland grows and shifts hormone production.

• Placenta takes over much of growth hormone secretion.

• Thyroid hormones shift, especially in early pregnancy.

• Cortisol (stress hormone) is about 3x higher than normal.

• Blood sugar runs lower, since so much glucose goes to fueling baby’s growth.

These hormonal shifts affect mood, energy, sleep, and metabolism—it’s a lot of work!

Gastrointestinal System: Why Digestion Feels Different

Ever wonder why heartburn, nausea, or constipation are so common?

• Delayed stomach emptying means food lingers longer.

• Slower GI transit can lead to bloating or constipation.

• Hormonal changes trigger nausea and vomiting in many women.

✨ Tips: Smaller meals, avoiding spicy foods, and staying hydrated can help ease these symptoms.

Hematological System: Big Changes in Your Blood

Your blood itself adapts in amazing ways:

• Plasma volume (the liquid part of blood) increases 30–50%.

• Red blood cells increase 18–25%.

• Hematocrit (blood concentration) actually decreases because plasma expands more than red cells.

This helps circulate oxygen more efficiently. But—it also explains why many women feel winded or fatigued. Your heart and lungs are simply working harder to keep up.

Musculoskeletal System: Shifts You Can Feel

Here’s where many women notice the most changes:

• Increased body mass from baby, placenta, fluids, and blood.

• Abdominal muscles stretch and lengthen as the uterus grows.

• Posture shifts: More arching in the low back (lumbar lordosis) and a forward pelvic tilt.

• Wider pelvis and joint laxity (from relaxin) prepare your body for birth.

• Center of gravity shifts forward, sometimes making you feel off-balance.

• Increased demand on hip muscles, calves, and pelvic floor.

➡️ Here’s an important note: While hormones like relaxin do loosen ligaments, aches and pains aren’t just about that. They’re often from the new physical demands placed on your muscles and joints. That’s where pelvic floor physical therapy can be incredibly helpful—supporting your body through these changes and reducing discomfort.

The Big Picture

Pregnancy is nothing short of remarkable. Every system in your body adapts—your heart, lungs, hormones, digestion, blood, muscles, and joints—all working together to grow and support life.

While some of these changes bring symptoms, understanding why they happen can help you feel empowered, not afraid. And remember—you don’t have to “just deal” with every ache or pain. With the right support, exercise, and care, pregnancy can be a lot more comfortable.

✨ You’re not just growing a baby—you’re growing an entirely new version of yourself. And that’s pretty incredible.

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