Pregnancy may be divided into several maturational phases, roughly corresponding to the three trimesters: by 12 weeks the fetus is properly formed and by 25 weeks or so it is viable if born. In addition to physiological changes, the mother-to-be is affected by hormonal and metabolic processes occurring in her body to sustain the pregnancy. Physical symptoms generate psychic interpretations and, conversely, emotional feelings, such as anxiety, fear or joy may reduce or enhance the physical effects. During the first phase of pregnancy, most women are acutely aware of their basic physical needs. Particularly during these early months, the expectant mother may find herself frequently preoccupied with her bodily functions and sensations, at times able to maintain only a minimal or superficial interest in most external things. The first stage of pregnancy is dominated not only by adaptation to the new state of being pregnant, but by the question of sharing it.