What Actually Happens to Your Pelvic Floor During Pregnancy

By the time your baby arrives, your pelvic floor has been carrying an increasing load for nine months. It has stretched, adapted, and compensated in ways that are completely normal - and completely invisible. Understanding what actually happens during pregnancy helps you make sense of the symptoms many new mums experience and gives you a realistic foundation for recovery.

The pelvic floor is not a single muscle

Before diving into what pregnancy does to it, it helps to understand what the pelvic floor actually is. It is a group of muscles, connective tissue, and fascia that forms a hammock-like base at the bottom of your pelvis. The main muscles include the levator ani group (pubococcygeus, puborectalis, and iliococcygeus) along with the coccygeus. These muscles support your bladder, uterus, and bowel, control continence, and play a role in sexual function.

Importantly, the pelvic floor works together with your deep abdominals (transversus abdominis), your diaphragm, and your deep spinal muscles as part of your core pressure management system. When one part of this system is disrupted - as pregnancy inevitably does - the whole system has to adapt.

How pregnancy loads the pelvic floor

The load your pelvic floor manages increases progressively throughout pregnancy. A full-term baby, placenta, and amniotic fluid can add 5-6 kilograms of direct downward pressure. As your uterus grows, your centre of gravity shifts forward, which changes how you hold your posture and alters the angle of force through your pelvis.

This increased load is constant - it does not switch off when you rest. Over nine months, your pelvic floor muscles and connective tissue adapt by lengthening and, in some cases, thinning. Research shows that by the third trimester, pelvic floor muscle thickness is measurably reduced compared to pre-pregnancy measurements. This is not damage - it is adaptation. But it does mean your muscles begin labour from a different starting point than they were at before conception.

The role of relaxin (and why it matters for recovery)

Relaxin is a hormone your body produces throughout pregnancy. It helps your ligaments and connective tissue become more pliable, which allows your pelvis to expand and create space for birth. This is a useful and necessary process - but it has a catch.

Relaxin does not selectively target only the ligaments involved in childbirth. It affects connective tissue throughout your body, including the fascial support structures around your pelvic organs. This is one reason why pelvic girdle pain, sacroiliac joint instability, and a general sense of "looseness" are so common during pregnancy. Your joints become less stable, and the pelvic floor is working harder to compensate.

Relaxin levels drop quickly after birth if you are not breastfeeding, but remain elevated during breastfeeding. This is why the postnatal period - particularly the first three to six months - requires a careful, progressive approach to rebuilding load capacity rather than jumping straight back into high-impact exercise.

Does birth type change outcomes?

Yes - though not always in the ways people expect. Vaginal birth, particularly instrumental delivery (forceps or ventouse), is associated with the highest risk of pelvic floor muscle damage and nerve injury. Research using MRI imaging has shown that levator ani muscle avulsion (tearing at the attachment point on the pubic bone) occurs in roughly 20-30% of vaginal deliveries. Many women are completely unaware this has happened.

Caesarean birth does not protect your pelvic floor entirely. Because the pelvic floor has carried the load of pregnancy for nine months regardless of how birth happens, caesarean-born women still commonly experience pelvic floor symptoms. C-section also introduces its own recovery considerations around scar tissue, altered abdominal muscle function, and core reactivation - which are covered in detail in a separate article.

What this means for your recovery

Understanding the timeline of what happened to your body helps set realistic expectations. Your pelvic floor did not simply "get weak" overnight - it adapted over nine months. Recovery follows a similar trajectory: gradual, progressive, and deeply individual.

Starting gentle pelvic floor exercises in the days after birth (when cleared by your care team) is appropriate for most women, but this is the beginning of a long process, not a quick fix. The 6-week postnatal check is often misunderstood as a clearance for all activity - we cover what it actually assesses (and what it misses) in the next article.

If you are experiencing leaking, heaviness, pain, or any other pelvic floor symptom, please know that these are common but not inevitable, and they respond well to the right rehabilitation approach. An individualised assessment from a pelvic floor physiotherapist is the most effective way to understand your specific situation.

The programme at Postnatal Recovery was designed by an AHPRA-registered pelvic health physiotherapist to guide you through exactly this process - starting where your body actually is, and building capacity safely and progressively.