Blood travels to all parts of an infant's body through vessels known as arteries. Blood pressure is the force of the blood, as it's pumped by the heart, against those arteries. A [normal blood pressure](http://www.uwhealth.org/health/topic/special/vital-signs-in-children/abo2987.html) for an infant from birth to six months is 65 to 90 systolic -- the top number in a blood pressure reading -- and 45 to 65 diastolic -- the bottom number in a blood pressure reading, according to the University of Wisconsin Hospitals and Clinics Authority.
Measuring Blood Pressure
An infant's blood pressure shows how hard her heart is working and how healthy her arteries are. Systolic blood pressure measures pressure in the arteries when the heart beats. Diastolic blood pressure measures pressure in the arteries between heartbeats, when the heart is resting and refilling with blood. Manometers -- instruments for measuring blood pressure -- measure pressure using a column of liquid, such as mercury, as it rises. An infant's blood pressure reading looks like two numbers separated by a slash, such as 72/48.
Normal Blood Pressure Range by Age
An infant's blood pressure range varies slightly depending on the age of the baby. Full-term, newborn infants to three months of age have a normal systolic reading from 65 to 85 and a normal diastolic reading from 45 to 55. Three- to six-month-old babies have a normal systolic blood pressure when it's between 70 and 90 and the diastolic pressure is between 50 and 65, according to the Nelson Textbook of Pediatrics.
High Blood Pressure Risks and Treatments
Several factors, such as hormones, the health of the heart and the health of the kidneys can cause an infant to have high blood pressure. In newborns, a blood clot in a kidney vessel -- often resulting from the use of an umbilical catheter to help a baby breathe better or allow medical staff to administer medications -- is often the cause. Exposure to illegal drugs, such as cocaine, while in the mother's womb, inherited conditions and thyroid problems can also lead to high blood pressure in infants. Most babies with high blood pressure won't have any symptoms other than those directly related to the condition that's causing the high blood pressure. Depending on the cause of the high blood pressure, a doctor might perform dialysis, prescribe medications or perform surgery.
Contact your health care provider if your baby doesn't grow or gain weight, has bluish-toned skin, gets frequent urinary tract infections or seems overly tired and irritable, recommends the U.S. National Library of Medicine. Take your baby to the emergency room immediately if she has seizures, vomits constantly or seems listless and doesn't respond to you.
Low Blood Pressure Causes and Treatments
Infants who experience low blood pressure usually do so shortly after birth. They may lose blood or fluid during or after delivery, resulting in reduced blood pressure, according to health services at the Meriter Hospital in Madison, Wisconsin. Infections and respiratory distress can also lead to low blood pressure. Medications that were given to the mother before delivery can lower a baby's blood pressure. Treatments include giving the baby extra fluid -- often containing albumin -- in her veins or putting her on medications designed to increase blood pressure. In serious cases of blood loss, a doctor might perform a blood transfusion using blood from a blood bank.