What happens to abdominal muscles while pregnant

The most obvious physical sign that a woman is pregnant is the growing abdomen – or, ‘baby bump’ – which affects the abdominal muscles. Understanding how the abdominal muscles work is helpful for pregnant women. Strengthening your abdominal muscles during and after pregnancy helps these muscles work as they should.

During pregnancy, the growing baby stretches the abdominal muscles. The mother's abdomen changes shape during the pregnancy because of the growth and movement of the baby, and so her abdominal muscles are also affected. For instance, the abdominal muscles progressively stretch as the pregnancy proceeds as the womb expands.
During the birth, most of the pushing is done by the uterus, not the abdominal muscles. After the birth, the abdominal muscles will feel weak and stretched, but these muscles should eventually become toned again.

Strengthening the abdominals can help pregnant women stay active and use the abdominal muscles for day-to-day activities, such as support and movement. Exercising abdominal muscles during pregnancy also helps them return to their original length and shape after the baby is born.

A safe way to work the abdominal muscles and improve core strength is to draw in the muscles without moving your spine – as though sucking your belly button in, towards the spine.
Pregnancy-specific exercise classes can also help build and maintain core strength, such as yoga and Pilates classes for pregnant women. They tend to focus on low impact exercises and feature movements that help with core strength, breathing and relaxation, strengthening abdominal muscles, the pelvic floor and relieving lower back pain.

Sources: Pregnanacy Birth Baby