Your baby has spent nine months floating in warm water. Here's what happens in your body when you join them.

Waterbirth isn't new. The first published study on birth in water appeared in France in 1805. In the 1980s, Dr. Michel Odent recorded the first 100 hospital waterbirths at Pithiviers, France. Today, hundreds of research papers have been published on waterbirth, documenting well over 150,000 births in water.

That's a lot of evidence behind something that also happens to feel wonderful. So what is warm water actually doing?

Waterbirth pioneer Barbara Harper describes the goal of water immersion with three words: comfort, peace, and relaxation. She calls water "CPR for labour."

This matters because of a well-known cycle in birth: fear leads to tension, and tension leads to pain. A frightened, tense body feels contractions more intensely, which creates more fear. Warm water interrupts that cycle at every point. It relaxes the muscles, calms the mind, and changes how pain is felt.

Your autonomic nervous system works in two broad modes. The sympathetic side runs "fight or flight." The parasympathetic side, including what polyvagal theory researcher Dr. Stephen Porges calls the ventral vagal "social engagement" system, handles safety, rest, and connection.

When fear takes over in labour, the body responds with a rush of adrenaline, fast breathing, a racing heart, and rising blood pressure. The body interprets the situation as unsafe for birth: oxytocin levels drop, labour can slow, and it becomes harder to think clearly or feel connected.

Warm water pulls the body in the other direction, toward feeling calm, centred, present, connected, and relaxed. It's one of the most reliable ways to reach that state during labour.

Your brain on water. Marine biologist Dr. Wallace J. Nichols spent years studying what he called the "Blue Mind," the calm, focused state people enter near water. Brain imaging research he highlighted suggests water environments are linked to higher dopamine and oxytocin and lower cortisol, the main stress hormone. Nichols explained that water offers both predictability and gentle novelty, letting part of the brain relax while staying softly alert.

For a labouring person, that looks like a dreamy, inward-focused state where they can feel the sensations of labour fully while staying aware of their surroundings. Many midwives recognize it instantly: the moment someone sinks into the pool and their whole face changes.

Water reduces the pull of gravity on the body, which gives a labouring person a new kind of freedom. Positions that would be exhausting on land become easy, and moving between them takes far less effort.

Water makes these positions easier to use:

• Kneeling opens the pelvis and supports baby's descent.
• Squatting maximizes space at the pelvic outlet and works with gravity.
• Side-lying promotes relaxation and gentle descent.
• Hands and knees relieves lower back pressure and helps baby rotate.
• Floating reclined reduces strain on the perineum and allows full rest between contractions.

Lying flat on the back, by contrast, tends to slow progress. Water makes it natural to avoid that position.

Buoyancy also helps people conserve energy. Being able to truly rest, even for a minute between contractions, adds up over a long labour.

Water presses evenly on every submerged part of the body. This hydrostatic pressure sets off a chain of physiological changes:

• Blood shifts from the arms and legs toward the chest, increasing circulating blood volume.
• The heart responds by releasing atrial natriuretic peptides (ANPs), hormones that help regulate fluid balance.
• Vasopressin, a hormone that normally holds onto water, decreases.
• The result is more urination and a shift in fluid balance, which is why swelling often eases in the tub.
• Oxytocin increases. This is one of the most important effects, since oxytocin drives contractions.
• Improved circulation supports oxygenation for both parent and baby.

These effects peak at around 90 minutes of immersion. This is one reason getting "in and out" of the pool works well. Changing environments periodically can give labour a fresh boost.

Birth researcher Dr. Sarah Buckley describes the hormones of labour as an "ecstatic hormonal cocktail," and water helps enhance it:

• Oxytocin, the hormone of love, powers contractions and bonding.
• Beta-endorphin, the hormone of pleasure and transcendence, is the body's own pain relief. In the first stage of labour, water immersion increases endorphin release, leading to deeper relaxation and less pain.
• Epinephrine and norepinephrine, the hormones of excitement, surge near the end of labour to give energy for birth and help baby transition.
• Prolactin, the hormone of tender mothering, supports bonding and breastfeeding.

These hormones build throughout labour. They don't just ease the experience; they orchestrate the actual process of birth. By lowering stress hormones and protecting this hormonal flow, water helps labour unfold the way the body designed it to.

• The Cochrane Review (2018) looked at 15 randomized controlled trials with over 3,000 participants and found that water immersion in labour reduces pain and lowers epidural rates, with no increased risk to newborns when proper protocols are followed.
• The Cluett study (2004), published in the BMJ, compared labouring in water with standard medical augmentation for people whose labour had stalled. Water was an effective alternative, with fewer interventions such as epidurals.
• Four meta-analyses of neonatal outcomes (Davies 2015, Taylor 2016, Vanderlaan 2018, and Burns 2022) found no increased odds of poor outcomes for babies born in water. Burns and colleagues' 2022 review, covering 35 studies, supports waterbirth as a safe non-drug option for managing labour pain.
• Large clinical studies across the UK, Australia, Turkey, Italy, and the United States found waterbirth was not associated with increased risk of severe tearing or postpartum hemorrhage. Fewer people in the waterbirth groups needed stitches for first- or second-degree tears.
• Large birth centre and home birth datasets from the American Association of Birth Centers and the Midwives Alliance of North America report high rates of spontaneous vaginal birth and newborn outcomes comparable to land births.

The consistent takeaway: for low-risk pregnancies, waterbirth is a safe and effective option when trained providers follow clear protocols.

It's the question we hear most. Babies have several built-in protections:

• Breathing practice stops. Babies make practice breathing movements in the womb, but these slow and stop during active labour to conserve oxygen.
• The lungs aren't "on" yet. Before birth, blood flow to baby's lungs is restricted by high resistance in the lung vessels. This doesn't change until after birth.
• Mild low oxygen during birth actually suppresses breathing movements rather than triggering them.
• The dive reflex. Baby's larynx is packed with chemoreceptors (five times more than the tongue). When water touches them, the airway closes and baby swallows instead of inhaling. This same reflex protects nursing babies from choking.

Baby is gently brought to the surface, often by the parent's own hands, and the first breath happens when their face meets the air.

For the birthing person: greater comfort and mobility, deeper relaxation, less pain, easier breathing, lower blood pressure, energy conservation, more control during pushing, fewer and less severe tears, and for many, a birth without narcotics or epidurals.

For baby: immediate, uninterrupted skin-to-skin contact, full expression of newborn reflexes, delayed cord clamping, a gentle transition "from womb to room," fewer stress hormones, and fewer NICU admissions.

• Get in when you need relief, especially as contractions grow stronger and more frequent. In-and-out works well.
• Keep the water comfortable, below 38°C (99°F). Your care team will record water temperature and monitor you throughout.
• Stay hydrated, and step out to cool off whenever you need to.
• Expect regular checks on baby. Providers listen to baby's heart rate at set intervals, and after every pushing contraction in the final stage.
• Water can also be used during pregnancy for relaxation, meditation, and bonding with baby.

Warm water works with the body's own design. It calms the nervous system, frees the body to move, shifts fluid and boosts oxytocin, and protects the powerful hormones that carry labour forward. The goal is simple: comfort, peace, and relaxation.

Talk with your midwife or care provider early in pregnancy about whether water is a good fit for you, and ask whether your birth setting has trained waterbirth providers.

Have a question? Send it in for Ask Away Wednesday, and follow @waterbirthcanada for more evidence-based waterbirth education.