Complex sentence: Moreover, many women are genetically predisposed to developing large breasts, the size and weight of which often are increased either by pregnancy or by weight gain, or by both conditions; there also exist iatrogenic causes, such as post-mastectomy and post-lumpectomy asymmetry.
Split into simpler sentences: Moreover, many women are genetically predisposed to developing large breasts, the size and weight of which often are aggravated either by pregnancy or by weight gain, or by both conditions. There also exist iatrogenic causes, such as post-mastectomy and post-lumpectomy asymmetry.