During the first trimester evidence of pregnancy is limited to missing a period and learning that the pregnancy test is positive. Some physical changes are apparent, such as fatigue, nausea, vomiting and breast tenderness. These symptoms are common and vary in intensity. Emotions are often unstable and feelings of depression are not uncommon, often for no apparent reason. It is commonly believed that the mood changes in pregnancy are caused by hormonal changes. The two main hormones that play a major role in pregnancy are estrogen and progesterone. A woman's emotions are characterized by mood swings, which can range from great joy to deep despair. Frequently a woman will become tearful with little cause. When asked why she is crying, she may find it difficult or impossible to give a reason. This situation is very unsettling for the husband or partner, causing him to feel confused and inadequate. Because the partner may feel unable to handle the woman's tears, he often reacts by withdrawing and ignoring the problem. Since the pregnant woman needs increased love and affection she may perceive her partner as unloving and nonsupportive. Once the couple understands that this behavior is normal in pregnancy it becomes easier for them to deal with although it will be a source of stress to some extent throughout the pregnancy.