In addition to checking for the conditions previously described, your doctor will also be looking for signs of a condition known as preeclampsia in your blood and urine. In the blood, this could be expressed by a low platelet count and in the urine, the presence of protein might indicate that the condition is present.
Preeclampsia affects 7 percent of all pregnant women, especially first-time mothers and those carrying multiple children [source: Bissinger]. It is a rising of the blood pressure due to the pregnancy and typically happens late term. It can have serious health risks for both mother and child, such as a lack of blood flow to the placenta or placental abruption (the pre-delivery separation of the placenta from the uterus). If it is left untreated, it can advance to eclampsia, in which the mother can experience life-threatening grand mal seizures.
This is why it is critical to closely monitor blood pressure throughout the pregnancy -- especially during the second half. But it's also important to realize that high-blood pressure alone does not mean preeclampsia is occurring. It must be verified with protein in the urine, as well.