When you are stressed, your body is constantly on the alert, ready to deal with a perceived threat. Your body prepares to attack or to flee by shunting blood away from your internal organs to your muscles. Your respiration rate increases, as does your adrenaline output and the pumping of your heart, none of which does you or your fetus any good in most instances. When you're dealing with truly difficult circumstances, such as the death of a loved one, illness, marital disharmony, financial problems, or any major change in your life, your endocrine system can get thrown out of whack. This may then affect the delicate hormonal balances of your body.
Some women find that their menstrual cycles become irregular when they are under stress.
Moreover, some research indicates it may be harder to become pregnant if you are very stressed. It's essential to take feelings of stress as seriously as you do an environmental hazard like smoking. Once you're pregnant, your fetus may suffer if you are extremely stressed. Normally, a moderate amount of stress probably isn't going to affect your pregnancy. The more prolonged the stress, however, the more likely it will take a toll on your body and, perhaps, on the fetus you carry.