Relaxed muscles and ligaments, poor posture... From the beginning of pregnancy, back pain, called lumbago, can appear.
From the first weeks of pregnancy, your muscles relax, especially your abdominal muscles, resulting in your pelvis tilting forward, creating an arch in your kidneys.
You're in such a hurry for everyone to see that you're pregnant! So, you naturally arch your back to get your belly out. To limit lower back pain, forget about heels, which tilt your pelvis forward more. Squat down often, knees apart, to stretch and relieve your lower back.
If the pain becomes unbearable, ask your obstetrician or midwife for advice.