Most pregnancy advice about swimming focuses on swelling, sleep, and back pain. All true. What gets less attention is what time in the water does for the nervous system, the breath, and the body’s preparation for labour. For mums hoping for a physiological birth, this matters more than most pregnancy guides let on.
What it is and why it matters
Physiological birth refers to labour and delivery that unfolds without routine medical intervention, supported by the body’s own hormonal and neurological processes. Preparation for it begins long before the first contraction. The state of the nervous system in late pregnancy shapes how labour starts, how it progresses, and how it feels. Water, used regularly, supports the breath, the body, and the nervous system at the same time.
What the research shows
Australian and international guidelines list swimming as a recommended form of exercise across all three trimesters. Australian Government physical activity guidelines recommend 150 to 300 minutes of moderate exercise per week during pregnancy, and swimming counts (Brown et al., 2022). The Royal Australian and New Zealand College of Obstetricians and Gynaecologists notes that water-based activities are particularly useful for managing oedema and joint pressure as pregnancy progresses, and that water keeps body temperature stable enough that no upper heart rate limit applies (RANZCOG, 2020).
Beyond fitness, immersion in warm water has measurable effects on the nervous system. Buoyancy reduces effective body weight by close to 90 percent, which is part of why women in labour often report instinctive relief on entering a birth pool. Time in water also shifts the body from sympathetic activation toward parasympathetic dominance, which lowers cortisol (Cluett, Burns, & Cuthbert, 2018).
This shift matters for birth. High cortisol and adrenaline interfere with the release of oxytocin, the hormone that drives labour contractions. A nervous system that has spent months learning to drop into a calm state under physical sensation is more likely to do so when labour begins.
Breath is the other quiet benefit. Submerging the body and exhaling slowly into the water is a low-effort version of the breath patterns recommended in physiological birth education, where long exhales support contractions and reduce pain perception. Research on water immersion in labour shows that the combination of buoyancy and slow breathing is associated with lower perceived pain and reduced use of pharmacological pain relief (Cluett et al., 2018). A large Danish cohort study of 74,486 pregnancies also found that women who swam in early to mid pregnancy had a slightly lower risk of preterm birth than non-exercisers (Juhl et al., 2010).
Practical strategies
- Aim for two to three sessions a week. Twenty to thirty minutes is enough. Consistency does more than length.
- Choose comfort over distance. Slow laps, gentle floating, or walking in chest-deep water all deliver the buoyancy and nervous system benefits. Speed adds nothing.
- Practise long exhales while submerged. Inhale through the nose above water, then exhale slowly through the mouth as the face goes under. This trains the same breath pattern used in labour.
- Skip breaststroke if there is pelvic girdle pain. The kicking action can aggravate pelvic instability. Freestyle, backstroke, or side stroke are gentler options.
- Keep water temperature in mind. Body temperature should not rise above 39°C in pregnancy. Lap pools and ocean swims are usually fine. Hot tubs and very warm spas should be limited.
- Stop if anything feels off. Lower abdominal pain, vaginal spotting, leaking fluid, contractions, dizziness, or an irregular heartbeat are reasons to leave the water and call a midwife, GP, or maternal child health nurse.
A real example
A woman in her third trimester is finding the last weeks heavy on her hips and lower back. Walking has become uncomfortable. She starts swimming twice a week at her local pool, doing twenty minutes of slow laps and another ten minutes floating on her back, practising long exhales as her face dips underwater. Within a fortnight, sleep improves and the constant ache eases. By the time labour starts, she has spent enough time in water to recognise the feeling of her body softening into it. When she steps into the bath at home in early labour, the response is automatic.
Red flags
Stop swimming and seek advice from a midwife, GP, or maternal child health nurse if there is vaginal bleeding, leaking fluid, contractions before 37 weeks, raised blood pressure, or any sense that something is not right. Swimming is not advised once waters have broken because of the risk of infection (RANZCOG, 2020).
Closing thought
Swimming in pregnancy is rarely framed as birth preparation. It tends to get filed under exercise. That undersells what it actually does. The body learns calm by repetition, and labour tends to go better when calm is already familiar.
References
Brown, W., Hayman, M., Haakstad, L. A. H., Mielke, G. I., Mena, G. P., Lamerton, T., Keating, S. E., Coombes, J. S., Mottola, M. F., & Evenson, K. R. (2022). Australian guidelines for physical activity in pregnancy and postpartum. Journal of Science and Medicine in Sport. https://www.health.gov.au/sites/default/files/documents/2021/05/evidence-based-physical-activity-guidelines-for-pregnant-women.pdf
Cluett, E. R., Burns, E., & Cuthbert, A. (2018). Immersion in water during labour and birth. Cochrane Database of Systematic Reviews, (5), CD000111.
Juhl, M., Kogevinas, M., Andersen, P. K., Andersen, A. N., & Olsen, J. (2010). Is swimming during pregnancy a safe exercise? Epidemiology, 21(2), 253–258.
Royal Australian and New Zealand College of Obstetricians and Gynaecologists. (2020). Exercise during pregnancy (C-Obs 62). https://ranzcog.edu.au/wp-content/uploads/Exercise-During-Pregnancy-Guidance.pdf
Sports Medicine Australia. (2016). Position statement: Exercise in pregnancy and the postpartum period.