Type 2 is the most common form of pelvic instability. Treatment is based on learning how to use the muscles around the pelvis more efficiently. Pelvic type 3:The ligaments do not support the joint sufficiently. This is a serious
situation whereby the muscles around the joint are unable to compensate for ligament weakness. This type of pelvic instability usually only occurs after an accident, or occasionally after a (small) accident in combination with giving birth. Sometimes a small accident occurring long before giving birth is forgotten so that the pelvic instability is attributed only to the childbirth. Although the difference between Type 2 and 3 is often difficult to establish, in case of doubt an exercise program may help the patient. However, if Pelvic Type 3 has been diagnosed then invasive treatment is the only option: in this case parts of the pelvis are screwed together. (Mens 2005)

Psychosocial impact
PGP in pregnancy seriously interferes with participation in society and activities of daily life; the average sick leave due to posterior pelvic pain during pregnancy is 7 to 12 weeks.In some cases women with PGP may also experience emotional problems such as anxiety over the cause of pain, resentment, anger, lack of self-esteem, frustration and depression; she is three times more likely to develop postpartum depressive symptoms. Other psychosocial risk factors associated with woman experiencing PGP include higher level of stress, low job satisfaction and poorer relationship with spouse.
Causes
Sometimes there is no obvious explanation for the cause of PGP but usually there is a combination of factors such as:

The pelvic joints moving unevenly. A change in the activity of the muscles in the pelvis, hip, abdomen, back and pelvic floor. A history of pelvic trauma. The position of the baby altering the loading stresses on the pelvic ligaments and joints. Strenuous work. Previous lower back pain. Previous pelvic girdle pain during pregnancy. Hypermobility, genetical ability to stretch joints beyond normal range. An event during the pregnancy or birth that caused injury or strain to the pelvic joints or rupture of the fibrocartilage. The occurrence of PGP is associated with twin pregnancy, first pregnancy and a higher age at first pregnancy. Mechanism
Pregnancy related Pelvic Girdle Pain (PGP) can be either specific (trauma or injury to pelvic joints or genetical i.e. connective tissue disease) and non-specific. PGP disorder is complex and multi-factorial and likely to be also represented by a series of sub-groups driven by pain varying from peripheral or central nervous system,
altered laxity/stiffness of muscles, laxity to injury of tendinous/ligamentous structures to mal-adaptive body mechanics.Pregnancy begins the physiological changes through a pattern of hormonal secretion and signal transduction thus initiating the remodelling of soft tissues, cartilage and ligaments. Over time, the ligaments could be stretched either by injury or excess strain and in turn may cause PGP. Anatomy
The pelvis is the largest bony part of the skeleton and contains three joints: the pubic symphysis, and two sacroiliac joints.