The abdominal wall is composed of four primary muscles: the superficial Rectus Abdominis (the “six-pack”), and the deeper External Obliques, Internal Obliques, and Transversus Abdominis. These muscles collectively provide posture, spinal support, and core stability by managing intra-abdominal pressure. During pregnancy, the body must accommodate the growing fetus, which directly impacts this muscular system. This involves mechanical stretching and hormonal adaptation so the abdominal wall can expand safely.
How the Abdominal Wall Adapts to Growth
The main mechanism that allows the abdomen to expand is the stretching and thinning of the connective tissue that runs down the midline, known as the Linea Alba. This fibrous band connects the two halves of the Rectus Abdominis muscle, extending from the breastbone to the pubic bone. As the uterus enlarges, it exerts immense pressure on the abdominal wall, causing the Linea Alba to elongate and widen.
Hormonal changes, particularly the increase in relaxin and progesterone, facilitate this process. These hormones soften the ligaments and connective tissues throughout the body, including the Linea Alba, making it more pliable and elastic. This softening allows the Rectus Abdominis muscles to separate and move laterally, creating space for the uterus without tearing the abdominal wall. This physical separation is a normal part of gestation, ensuring the growing baby has adequate room.
The Reality of Diastasis Recti
Diastasis Recti (DR) is defined as an excessive widening of the gap between the right and left sides of the Rectus Abdominis muscles. It is not a tear of the muscle itself, but rather an overstretching or thinning of the Linea Alba connective tissue that joins them. Up to 100% of pregnant women experience some degree of this separation by the third trimester.
The separation can occur anywhere along the midline, but it is often widest at or just above the umbilicus. Diastasis Recti is typically diagnosed when the inter-recti distance (IRD) measures 2.7 centimeters or greater. Clinicians often use finger widths to quickly measure the gap, though ultrasound provides a more objective assessment.
For many women, the separation naturally begins to lessen in the first eight weeks postpartum as the hormones decrease and the abdominal wall starts to recover. However, for a significant number of women, the separation may persist, with prevalence rates ranging from 35% to 60% in the immediate postpartum period. This persistent widening can result in a visible bulge or “pooch” in the abdomen, sometimes referred to as “doming” or “coning” when the abdominal muscles are tensed.
Functional Changes in the Deep Core
The abdominal changes extend beyond the superficial “six-pack” muscles to the deep core unit, which provides spinal stability and postural support. The Transversus Abdominis (TVA) is the deepest layer, acting like a natural corset that wraps horizontally around the torso. This muscle works in close coordination with the diaphragm, the multifidus muscles, and the pelvic floor muscles to manage intra-abdominal pressure.
During pregnancy, the TVA is significantly lengthened and weakened due to the continuous expansion of the uterus. This lengthening compromises its ability to provide circumferential support, which contributes to instability in the spine and pelvis. The altered mechanics can lead to common complaints such as lower back pain and pelvic girdle pain.
The co-activation pattern between the TVA and the pelvic floor muscles becomes compromised in pregnant and postpartum women. This disruption reduces the body’s ability to reflexively brace and stabilize the core before movement, impairing overall body mechanics. Restoring this functional connection, separate from closing the Diastasis Recti gap, is a primary goal of postpartum rehabilitation.
Postpartum Healing and Safe Movement
The initial phase of postpartum recovery is a time when stretched tissues and muscles begin to heal. The body naturally starts to recover as pregnancy hormones, like relaxin, diminish, allowing ligaments and muscles to gradually regain tone. However, a measured and progressive approach to movement is necessary to prevent strain on the still-healing Linea Alba.
Immediately postpartum, the focus should be on gentle core reconnection, primarily through diaphragmatic breathing exercises. These breathing techniques help to re-engage the deep Transversus Abdominis and pelvic floor without increasing excessive intra-abdominal pressure. Movements that cause the abdomen to visibly bulge or “cone,” such as traditional crunches, full sit-ups, and heavy lifting, should be avoided initially.
Consulting a pelvic floor physical therapist (PFPT) is often recommended. A PFPT can assess the degree of any persistent Diastasis Recti and the functional coordination of the deep core muscles, providing an individualized rehabilitation plan. Recovery is not a fixed timeline, as healing can take many months, and a slow progression is the safest path to rebuilding foundational strength.