The Infant and Adolescent Uterus
The uterus grows progressively during fetal life. After birth, uterine volume is relatively higher, longer and thicker than the prepubertal uterus and shows endometrial and myometrial characteristics very similar to those of adults.

After the first weeks, uterus size regresses, probably because of the withdrawal of maternal hormone stimulation. During childhood the uterus shows no changes in size and shape until the age of 7 years (

fig. 1). From this age onward, uterine volume increases progressively at a slow rate before the appearance of secondary sexual characteristics. A sharp acceleration is seen during puberty, which has a good correlation with Tanner stages (

fig. 2 - Uterine volume according to pubertal stage.), age, weight, height and estradiol levels, and the most dramatic changes are seen between stages 3 and 4 of breast development.

After menarche, the uterus continues to grow, even after the almost complete development of the secondary sexual characteristics. Menarche is a critical step toward the development of the whole reproductive system, especially of the uterus, which assumes a new function. After menarche, uterine growth rate slows and gradually tends to take on the adult size and structure.

However, normal adult values are not attained even by the sixth gynecologic year (

fig. 3), which shows that full development of this reproductive organ takes even more time, although adult morphology and corpus/cervix ratio are already achieved by menarche.

Among the reproductive hormones, estradiol seems to be the main agent for uterine growth. Other reproductive parameters, such as the frequency of menstrual bleeding and that of ovulation and progesterone levels, do not appear to be related to uterine size and growth rate.

Height and weight correlate with uterine volume before menarche but not afterward, since at this age they have nearly exhausted the developmental changes and vary independently of growth factors. The adrenal steroids dehydroepiandrosterone and dehydroepiandrosterone sulfate, which are reliable indexes of biologic maturation, continue to increase during adolescence and, interestingly, they correlate with uterine development.

The finding of a still small uterus during adolescence may have reproductive implications. The lack of complete genital tract maturity might partly account for problems such as preterm labor, preeclampsia, and small-for-gestational age infants; these problems are not uncommon in adolescence.

The ovarian/uterine ratio decreases with increasing gynecologic age (

fig. 3).

The mean value at the first gynecologic year is very similar to that found in the polycystic ovary syndrome, probably because, unlike the uterus, the ovaries seem to have already reached complete growth at menarche. Furthermore, their volume often exceeds the adult value and needs a reduction in size to reach the final maturational step.