The pressure due to a liquid in liquid columns of constant density or at a depth within a substance is represented by the following formula:

  
    
      
        p
        =
        ρ
        g
        h
        ,
      
    
    {\displaystyle p=\rho gh,}
  where:

p is liquid pressure,
g is gravity at the surface of overlaying material,
ρ is density of liquid,
h is height of liquid column or depth within a substance.Another way of saying the same formula is the following:

  
    
      
        p
        =
        
          weight density
        
        ×
        
          depth
        
        . {\displaystyle p={\text{weight density}}\times {\text{depth}}.}
In some cases it can come on suddenly or following a fall, sudden abduction of the thighs (opening too wide too quickly) or an action that has strained the joint. PGP can begin as early as the first trimester of pregnancy. Pain is usually felt low down over the symphyseal joint, and this area may be extremely tender to the touch. Pain may also be felt in the hips, groin and lower abdomen and can radiate down the inner thighs. Women with PGP may begin to waddle or shuffle, and may be aware of an audible clicking sound coming from the pelvis. PGP can develop slowly during pregnancy, gradually gaining in severity as the pregnancy progresses. During pregnancy and postpartum, the symphyseal gap can be felt moving or straining when walking, climbing stairs or turning over in bed; these activities can be difficult or even impossible. The pain may remain static, e.g., in one place such as the front of the pelvis, producing the feeling of having been kicked; in other cases it may start in one area and move to other areas. It is also possible that a woman may experience a combination of symptoms. Any weight bearing activity has the potential of aggravating an already unstable pelvis, producing symptoms that may limit the ability of the woman to carry out many daily activities. She may experience pain involving movements such as dressing, getting in and out of the bath, rolling in bed, climbing the stairs or sexual activity.