Problems with the birth canal include a narrow vagina and perineum which may be due to female genital mutilation or tumors. All of these factors lead to a failure in the progress of labor. Evolution
Obstructed labor is more common in humans than any other species and continues to be a main cause of birth complications today. Modern humans have morphologically evolved to survive as bipeds, however, bipedalism has resulted in skeletal changes that have consequently narrowed the pelvis and the birth canal. The combination of increased brain size and changes in pelvic structure are the major contributors of obstructed labor in modern humans. It is also common for obstructed labor in humans to be caused by the fetus’ broad shoulders. However, morphological shifts in pelvic structure still account for the inability of a fetus to effectively pass through the birth canal without major complications Other primates have a wider and straighter birth canal that allows a fetus to pass through more effectively. Mismatch between birth canal size and infant cranial width and length due to bipedal locomotion requirements have often been referred to as the obstetric dilemma, since compared to other great apes, modern humans have the greatest disproportion between infant cranial size and birth canal size. Shrinking of upper extremities and curvature of the spine have also affected the way modern humans give birth. Quadruped apes have longer upper limbs that allow them to reach down and pull their fetus out of the birth canal unassisted.
Four of the following seven specific symptoms should be present:
Avoids occupational activities that involve significant interpersonal contact, because of fears of criticism, disapproval, or rejection
is unwilling to get involved with people unless certain of being liked
shows restraint within intimate relationships because of the fear of being shamed or ridiculed
is preoccupied with being criticized or rejected in social situations
is inhibited in new interpersonal situations because of feelings of inadequacy
views self as socially inept, personally unappealing, or inferior to others
is unusually reluctant to take personal risk or to engage in any new activities because they may prove embarrassing

Differential diagnosis
In contrast to social anxiety disorder, a diagnosis of avoidant personality disorder (AvPD) also requires that the general criteria for a personality disorder be met. According to the DSM-5, avoidant personality disorder must be differentiated from similar personality disorders such as dependent, paranoid, schizoid, and schizotypal. But these can also occur together; this is particularly likely for AvPD and dependent personality disorder. Thus, if criteria for more than one personality disorder are met, all can be diagnosed.There is also an overlap between avoidant and schizoid personality traits (see Schizoid avoidant behavior) and AvPD may have a relationship to the schizophrenia spectrum.Avoidant personality disorder must also be differentiated from the autism spectrum, specifically Asperger syndrome.