Why lung capacity increases by nearly 50% during pregnancy: both tidal volume and respiratory rate rise

Breathing for two: how pregnancy reshapes the lungs (without turning it into a science lecture)

Let’s start with a simple truth many expectant parents notice in the second and third trimesters: your breathing shifts. Not just a little—a lot. And the reasons are a mix of biology, hormones, and good old human adaptability. In everyday terms, pregnancy helps your lungs become more efficient, so each breath can carry more oxygen to both you and your baby. The quick takeaway: the two big changes are bigger breaths and a touch faster breathing. When you put those together, you’ve got a near 50 percent boost in how much air your body can move around with each cycle. Here’s what that means and why it matters.

Two changes that truly matter

• Each breath has a greater volume (tidal volume). In pregnancy, the lungs take in more air per inhale. The diaphragm can stretch a bit deeper, and the air you pull in with each breath isn't just filler—it’s more oxygen that your body can use right away. Think of it as widening the pipe through which air travels so more oxygen can reach the blood quickly.

• The rate of breathing increases slightly. You’ll notice your breaths aren’t as shallow as they used to be. There’s a gentle nudge upward in breathing frequency, so you’re not just taking deeper breaths—you’re taking more of them, too. It’s not a dramatic sprint; it’s a steady, helpful uptick that keeps the oxygen flowing as your metabolism climbs.

If you’ve ever tried to sprint while wearing a backpack, you know how air needs to work a little harder to keep you going. Pregnancy works in a similar way, but the body makes the adjustments quietly and efficiently, so you don’t have to worry about it every moment. The combination of bigger breaths and a faster rhythm translates into more oxygen delivered to both you and the developing fetus. That oxygen is the fuel that supports fetal growth and the extra metabolic tasks you’re handling as pregnancy progresses.

What’s happening inside the body (the short version)

• The diaphragm’s job is a little different now. It still does the same drumbeat—move down when you inhale, relax up when you exhale—but pregnancy changes the space inside your chest. The diaphragm can move with a little more freedom than you might expect, thanks to posture shifts and hormone-driven changes in tissue elasticity. The result? Deeper, more efficient breaths.

• Hormones join the party. Progesterone, in particular, tends to boost the respiratory center in your brain, nudging your body to ventilate a bit more. Think of it as your body’s way of “double-checking” that there’s enough oxygen for both you and baby, especially as your blood volume expands and your tissues require more oxygen.

• The uterus isn’t cheek-by-jowl with the lungs all the time, but as it grows, it does influence how you breathe. The body’s clever adaptation isn’t about cranking up the volume alone; it’s about shifting the whole breathing pattern toward efficiency—deeper breaths taken with a comfortable regularity.

So yes, both bigger breaths and a slightly quicker breathing rate work together to improve respiratory efficiency during pregnancy. If you’re doubling up oxygen delivery to two people at once, that’s a win worth understanding and supporting.

What this means for you as a doula (the practical side)

Breathing is a powerful tool in labor and delivery, but it starts long before contractions ramp up. For expectant parents, understanding the way breaths change during pregnancy helps you guide and support with confidence.

• Normal lab behavior is not “just breathing.” It’s about teaching and reinforcing techniques that keep oxygen flow steady and stress levels lower. When a birthing person uses diaphragmatic breathing and audible exhale patterns, they’re using the body’s natural adjustments to stay calm and focused.

• Labor breathing matters. During contractions, oxygen demand spikes. Having practiced breathing patterns that align with the body’s increased tidal volume can help sustain energy and reduce sensations of breathlessness. It’s not about “pushing” harder—it’s about optimizing each breath.

• Posture and comfort influence breathing. A slouched neck or rounded shoulders can restrict airflow. Encouraging relaxed shoulders, an open chest, and a supported seat or bed position can make those deeper breaths feel easier.

A simple breathing routine you can share (and practice together)

Try this easy routine with clients or even for yourself. It’s friendly, not scientific, and it honors the body’s natural changes.

• Find a comfortable seat or lie on your side. Place one hand on your belly and the other on your chest. Notice how your breath moves. If your belly rises more with each inhale, you’re engaging diaphragmatic breathing—good job.

• Inhale slowly through the nose for a count of four. Let the chest stay relatively soft; the belly should rise as the diaphragm drops.

• Exhale gently through the mouth with a pursed-lip feel for a count of six to eight. A longer, slower exhale supports relaxation and helps oxygen delivery stay smooth.

• Repeat for five to ten minutes, a few times a day. If you’re in labor, use a paced pattern that matches contractions—longer, slower exhalations through the peak of the contraction, with a natural reset on the exhale.

A natural digression that fits here: many people are surprised at how much breath work overlaps with everyday life. A calm, deliberate breathing pattern isn’t just for birth—it helps during sleep, stress, and even when you’re chasing a toddler around the kitchen. The brain learns from consistency, so practicing a simple breath routine can pay dividends far beyond labor.

A note on staying safe and supported

Breathing is intimately tied to overall health, and pregnancy isn’t a time for guesswork. Encourage pregnant people to:

• Check in with a healthcare provider about any respiratory symptoms, especially if there’s shortness of breath, wheeze, or chest tightness.

• Stay hydrated and comfortable. Dehydration can influence breathing and energy, and a warm, breathable environment makes deep breaths feel easier.

• Move gently. Regular, moderate activity (as advised by a clinician) supports lung capacity by keeping muscles flexible and the chest open.

If you’re assisting during labor, understand that every person breathes a little differently. Some will be naturally rapid and shallow early on; others will gravitate toward slower, deeper breaths. Your job isn’t to force a “perfect” pattern, but to guide and normalize a comfortable rhythm that keeps both mom and baby well-oxygenated.

Why this matters for doulas, in plain terms

Two big ideas.

1. Oxygen efficiency is central. Your focus on breath supports energy, stress management, and fetal well-being. The physiologic shift—more air per breath plus a gentle uptick in breathing rate—helps explain why breathing techniques feel so grounding during labor.

2. Education builds confidence. When you can explain in simple terms what’s happening—“breath is deeper, breath comes a bit quicker, and that’s helping everyone stay topped up”—parents feel steadier. Confidence matters in birth, and breathing is a reliable, empowering anchor.

A few quick reminders to keep in mind

• The “why” matters. It’s not about depth for depth’s sake; it’s about sustainable oxygen delivery as the body’s demands grow.

• Your tone should be calm and practical. People respond to clear, compassionate guidance, not lectures.

• Respect individual variation. Some parents love longer breaths; others prefer shorter, quicker cycles. The best approach is the one that keeps them relaxed and focused.

A gentle closer

Pregnancy nudges your breathing in big, helpful ways. The lungs aren’t producing miracles out of thin air; they’re adapting in practical, human-friendly ways—deeper breaths, a touch faster rhythm, and a readiness to fuel two lives at once. For doulas, that translates into a powerful doorway to support: you help people notice, practice, and trust their breath as labor begins and unfolds.

So, next time you’re chatting with someone about what changes during pregnancy, you can share this: lung capacity doesn’t just magically appear bigger; it’s a duet—bigger breaths and a slightly quicker pace—that makes room for the growing needs inside. And in the right hands, that knowledge becomes a calm, confident presence at one of life’s most meaningful moments.