What actually happens to your core during and after pregnancy
Pregnancy changes the core system in ways that take longer to reverse than most women are told. The hormone relaxin, produced throughout pregnancy and peaking around 10-14 weeks, softens connective tissue throughout the body — including the pelvic floor ligaments and the linea alba (the connective tissue between the abdominal muscles). This softening is necessary to allow the pelvis to expand during birth but means the supporting structures of the core are significantly less rigid postpartum than they were pre-pregnancy. Relaxin levels remain elevated during breastfeeding. The practical implication is that the connective tissue structures supporting the pelvic organs and abdominal wall are still genuinely more vulnerable in the weeks and months after birth than most exercise advice acknowledges.
Childbirth — vaginal or caesarean — also directly affects the muscles, nerves, and connective tissue of the pelvic floor. Vaginal birth can cause stretching, tearing, or nerve injury to the levator ani muscle complex. Caesarean section involves cutting through the rectus sheath and uterine wall — two surgical wounds, not just one. Both require tissue healing before progressive loading, and both have different timelines and considerations.
The staged return that actually works
The 2019 UK guidelines on postnatal return to running (Groom, Donnelly, Brockwell) established a framework that has been broadly adopted by pelvic health physiotherapy. It is built on the principle that the pelvic floor must be able to manage load before that load is increased. The stages are not arbitrary time cutoffs — they reflect the healing timeline of connective tissue and the progressive loading principles of sports rehabilitation applied to the postnatal body.
The caesarean section timeline is often underestimated: A c-section involves cutting through multiple tissue layers including the rectus sheath, the peritoneum, and the uterine wall. Wound healing of the uterine scar takes 6-12 weeks for the initial closure, but full scar tissue maturation takes 6-12 months. Loading the abdominal wall (including coughing, lifting, and core exercises) before adequate scar healing is established puts stress on immature tissue. Pelvic health physiotherapy assessment after a caesarean should specifically include scar mobilization and assessment of scar sensitivity and adhesion before returning to core loading — a step that most postnatal care programs skip entirely.
- Weeks 1-6 — healing phase: Walking (short distances, building gradually), diaphragmatic breathing, gentle pelvic floor activation. No impact, no heavy lifting. A pelvic health physio assessment in this phase is useful if you had any perineal trauma, a difficult birth, or a caesarean — don't wait for the 6-week check if you have symptoms.
- Weeks 6-12 — foundation phase: This is where core rehabilitation begins in earnest — bodyweight exercises, clinical pilates, swimming from around 8 weeks, low-impact activity. The 6-week clearance from your GP or midwife is a wound-healing check, not a fitness clearance. A pelvic health physiotherapist provides the exercise clearance.
- Week 12+ — progressive loading phase: Return to running, HIIT, and higher-impact exercise is appropriate now for women who have no pelvic floor symptoms. The readiness tests from Groom et al. (2019) include: walking 30 minutes without symptoms, single-leg balance 10 seconds, single-leg calf raises 20 reps, and single-leg bridge 10 reps — all without leakage, pain, or prolapse sensation.
- Ask specifically about pelvic floor assessment: Many women go months or years with manageable but persistent symptoms — mild leakage, back pain, a feeling of heaviness — assuming this is "normal after having a baby." It often responds well to treatment. A pelvic health physiotherapy referral at any point postpartum is appropriate, not just in the early weeks.
Stop-signs that warrant prompt assessment rather than waiting: any leakage (urine, wind, or stool) during exercise or daily activity, a feeling of heaviness or bulging in the vaginal area (which could indicate prolapse), pain with exercise or intercourse, or abdominal doming during movement. These are not inevitable or permanent postpartum changes — they are symptoms that respond well to treatment when addressed rather than pushed through.
- Groom T, Donnelly G, Brockwell E (2019). Returning to running postnatal — guidelines for medical, health and fitness professionals managing this population. Journal of Women's Health Physical Therapy, 43(2):73-85.
- Bø K et al. (2017). Exercise and pregnancy in recreational and elite athletes. British Journal of Sports Medicine, 51(8):543-544.
- Dumoulin C et al. (2018). Pelvic floor muscle training versus no treatment, or inactive control treatments, for urinary incontinence in women. Cochrane Database of Systematic Reviews, 10:CD005654.
- MacLennan AH et al. (2000). The prevalence of pelvic floor disorders and their relationship to gender, age, parity, and mode of delivery. BJOG, 107(12):1460-1470.
- Wesnes SL et al. (2021). Urinary incontinence and overactive bladder in women postpartum — a systematic review. International Urogynecology Journal, 32(7):1975-1990.