At month five, the vaginal canalization is complete and the fetal hymen is formed from the proliferation of the sinovaginal bulbs (where Müllerian ducts meet the urogenital sinus), and normally becomes perforate before or shortly after birth.The hymen has dense innervation. In newborn babies, still under the influence of the mothers hormones, the hymen is thick, pale pink, and redundant (folds in on itself and may protrude). For the first two to four years of life, the infant produces hormones that continue this effect. Their hymenal opening tends to be annular (circumferential). Post neonatal stage, the diameter of the hymenal opening (measured within the hymenal ring) widens by approximately 1 mm for each year of age. During puberty, estrogen causes the hymen to become very elastic and fimbriated. The hymen can stretch or tear as a result of various behaviors, by the use of tampons or menstrual cups, pelvic examinations with a speculum, sexual intercourse, insertion of multiple fingers or items into the vagina, and activities such as gymnastics (doing the splits), horseback riding or trauma caused by a "straddle injury". Remnants of the hymen are called carunculae myrtiformes.A glass or plastic rod of 6 mm diameter having a globe on one end with varying diameter from 10 to 25 mm, called a Glaister Keen rod, is used for close examination of the hymen or the degree of its rupture.
Imperforate: hymenal opening nonexistent; will require minor surgery if it has not corrected itself by puberty to allow menstrual fluids to escape. Cribriform, or microperforate: sometimes confused for imperforate, the hymenal opening appears to be nonexistent, but has, under close examination, small perforations. Septate: the hymenal opening has one or more bands of tissue extending across the opening. Trauma
Historically, it was believed that first sexual intercourse was necessarily traumatic to the hymen and always resulted in the hymen being "broken" or torn, causing bleeding. However, research on women in Western populations has found that bleeding during first intercourse does not invariably occur. In one cross-cultural study, slightly more than half of all women self-reported bleeding during first intercourse, with significantly different levels of pain and bleeding reported depending on their region of origin. Not all women experience pain, and one study found a correlation between the experience of strong emotions – such as excitement, nervousness, or fear – with experiencing pain during first intercourse.In several studies of adolescent female rape victims, where patients were examined at a hospital following sexual assault, half or fewer of virgin victims had any injury to the hymen. Tears of the hymen occurred in less than a quarter of cases. However, virgins were significantly more likely to have injuries to the hymen than non-virgins.In a study of adolescents who had previously had consensual sex, approximately half showed evidence of trauma to the hymen. Trauma to the hymen may also occur in adult non-virgins following consensual sex, although it is rare.