The vaginal epithelium is sensitive to hormonal influence. Sequential
changes occur throughout the life cycle, including during birth,
childhood, puberty, menstrual cycles, pregnancy, and menopause.
At birth, the vagina is 4 cm long, lengthens approximately 1
cm during early childhood and 8 cm during late childhood, and reaches
mature length of 10 to 12 cm by menarche. The vagina at birth resembles
the mature vagina with deep cryptic rugae and folds secondary to
maternal estrogenic effect. As maternal estrogen levels fall in
the infant, the vaginal wall becomes dry, thin, nonelastic, and
nonrugated. The vagina remains in this quiescent state until the onset
of puberty. During early puberty, increased estrogen levels affect
the vaginal epithelia. Such pubertal changes can be noted on examination
by identification of the more mature dull pink color of the vaginal
mucosa, increased vaginal secretions, and increased vaginal wall flexibility
compared with the prepubertal findings of the red translucent mucosa,
sparse secretions, and a relatively rigid vaginal wall. The distal
third of the vagina is one of the first sites to be affected by
estrogen during puberty. The vaginal epithelium is made of 4 cell
layers: basal, parabasal, intermediate, and superficial. The histology
of the infant shows vaginal epithelium with a predominance of basal
cells. In early childhood, the epithelium is 2 to 8 layers thick and
consists of a definitive basal layer and parabasal intermediate
cells. With the small increases of estrogen in late childhood, the
intermediate cell layer proliferates, and the superficial cells undergo
maturation. In the middle of puberty, the rise in estrogens results
in the cornification (transformation of cell type) of the epithelium and
development of a tissue layer 65 to 85 cells thick, which consists
of predominantly mature squamous superficial cells. Up to 12 months
before menarche, an increase in vaginal secretions may be noted,
resulting from desquamated superficial and intermediate cells and
mucoid secretions from maturing cervical and vestibular glands.1 These
secretions are often reported by patients as a discharge with concerns
about possible infection. The patient needs to be reassured about
this normal physiologic process.
After birth, the neonatal vagina is temporarily colonized with
lactobacilli that produce lactic acid, resulting in an acidic milieu.
Within several weeks after birth, the vaginal flora changes and becomes
predominantly colonized with enterococci and diphtheroids, and the
pH becomes alkaline. This environment persists through childhood
until puberty, when lactobacilli reappear in greater concentrations
and again produce an acidic vaginal milieu. Colonization with H2O2-producing
lactobacilli seems to be important for vaginal microbiological health and
protection against infections such as human immunodeficiency virus
(HIV).2 With the maturation of the
vagina after menarche, cyclic changes in the vaginal histology occur
with the menstrual cycle. Vaginal cytology can be helpful in evaluating
the estrogen effect. The estrogen-induced vaginal changes provide
a primary barrier to local trauma and infection. Cyclic
changes in histology linked to the monthly rhythmic variations in
both estrogen and progesterone are not established until the ovarian
cycle matures 1 to 2 years postmenarche.