Ovarian Development during Puberty and Adolescence

Before the increasingly common use of ultrasound evaluation of the ovaries, anatomical and histological descriptions gave us a dynamic image of the developing ovary documenting that during childhood the ovary is never at rest and follicles grow and degenerate continuously. Peters et al. identified three steps of ovarian growth: the quiescent ovary, with small resting follicles and occasional preantral follicles; the ovary in early growth, with small follicles, preantral follicles and occasional antral follicles not larger than 0.5mm; and the actively growing ovary that is more and more frequent after the age of 6 when antral follicles, which are usually well distended, become increasingly numerous and large. These follicles have been called 'cystic' but they are normal follicles, some of them healthy, others in degeneration.

The ovarian size increases throughout childhood in relation to a gradual increase in the number as well as in the size of the antral follicles and a progressive increase of the stroma derived from follicle atresia. Besides multiple follicle growth and atresia, partial luteinization of the theca interna and fibrosis of the cortex are common features in the normal process of follicular development throughout infancy and childhood, so that early pubertal ovaries have been described that are indistinguishable from those of the polycystic ovary syndrome.

The advent of ultrasound has enabled clinicians to easily examine ovaries of a large number of girls and, moreover, to follow their development (fig. 4).

Antral follicles or microcysts not exceeding 9 mm, as defined by ultrasound, start to increase around the age of 9 with the appearance of fluid areas >9mm after the age of 11.

Fig. 4. Ultrasound ovarian appearance before puberty (a) and after puberty onset (b) [from 1].

In the years immediately before menarche, the cystic structure becomes prevalent. The increase in cystic structure coincides with the beginning of the gonadotropin rise which seems to play a central role in the last stages of follicular development. At this age gonadotropin secretion changes its quality, enhancing its pulsatile characteristics, both episodic and circadian, and sending a faster and more fluctuating signal to the ovaries which accelerate the turnover of follicular development. The follicles increase in size and steroid production.

Figure 5 shows an early pubertal nocturnal rise of LH, with levels remaining very low during the day. However, only a few nocturnal pulses are sufficient to promote the progression of some follicles in the still small ovaries. A higher number of LH pulses can occasionally be present also during the day in premenarcheal girls at mid and late puberty when ovaries show a higher volume and number of follicles compared to the previous stage (). In fact there is a positive correlation between Tanner stages and ovarian volume .