A system and method for monitoring and estimating the blood pressure of a pregnant patient that modifies the blood pressure estimating algorithm when the patient is pre-eclamptic. The level of carbon monoxide within a patient's bloodstream or exhaled breath can be analyzed to determine whether a pregnant patient is pre-eclamptic. After the patient has been diagnosed as pre-eclamptic, the NIBP monitoring system adjusts its algorithm for estimating the patient's blood pressure to compensate for the physical changes that occur in the patient during pre-eclampsia. The adjusted blood pressure estimates calculated by the NIBP monitoring system can be calculated using different adjustment techniques and methods and are displayed on the NIBP monitor.