Developing follicles begin to grow when follicle-stimulating hormone (FSH) is released by the hypothalamus. This brings about the growth of the egg-containing follicles and makes them produce estrogen, which encourages the growth of breasts, widens the pelvis, and encourages the development of the external genitals. The rising level of estrogen in the bloodstream causes the hypothalamus to reduce amycontentbreak second substance, luteinizing hormone (LH). This causes one of the follicles to burst and release an ovum for possible fertilization.