If any adverse circumstances affect pregnancy endangering either mother or baby's health or outcome of pregnancy , termed as high risk cases. They need extra care & timely intervention to improve the outcome.
Other preexisting medical conditions like high blood pressure, diabetes, or heart, breathing, or kidney problems & infections can become more serious during a woman's pregnancy.
Although pregnancy is a normal process of life, but it has lots of effect on mother's body. Many changes occur in her which can worsen the existing disease, precipitate the occult health problems or can give rise specific diseases only related to pregnancy. In old time there is a saying that a woman has a rebirth after delivery, it is true in cases of high risk pregnancy.