Symphysis pubis dysfunction (SPD) is a problem with the pelvis. Your pelvis is mainly formed of two pubic bones that curve round to make a cradle shape. The pubic bones meet at the front of your pelvis, at a firm joint called the symphysis pubis.
The joint’s connection is made strong by a dense network of tough tissues (ligaments). During pregnancy, swelling and pain can make the symphysis pubis joint less stable, causing SPD.

Doctors and physiotherapists classify any type of pelvic pain during pregnancy as pelvic girdle pain (PGP)
SPD is one type of pelvic girdle pain. Diastasis symphysis pubis (DSP) is another type of pelvic girdle pain, which is related to SPD. DSP happens when the gap in the symphysis pubis joint widens too far. DSP is rare, and can only be diagnosed by an X-ray, ultrasound scan or MRI scan

Original article: https://www.babycentre.co.uk/a546492/pelvic-pain-in-pregnancy-spd