Growth of the birth canal in adolescent girls.

The growth and development of four dimensions of the pelvic birth canal are analyzed from a longitudinal sample of 9 well-nourished girls aged 8 through 18. Compared with stature, the pelvic basin grows more slowly and continuously through late adolescence. Similarly, size of the birth canal is smaller the first 3 years past menarche than at age 18. At low gynecologic ages, a significantly greater percentage of growth to adult size is required in the pelvis as compared to stature, and growth of the birth canal continues beyond the asymptote for statural increase. The pelvis is smaller and less mature among girls with early menarche than among girls with late menarche at the same menarcheal ages. These results indicate that immaturity of the birth canal of the pelvis may have significance for obstetric risks among young teenage primiparous girls.