Blood clots are among the rarer health issues that can occur during pregnancy. Though they are uncommon, it's helpful to know which women are at the highest risk for developing one.
A recent study looked at several hundred thousand pregnant women to see what risk factors were linked to blood clots.
The researchers found that women with several medical problems before pregnancy were at a higher risk for having a blood clot during pregnancy.
Women who had stillbirths, pregnancy complications or several other medical conditions were at higher risk for a blood clot after giving birth.
The study, led by Alyshah Abdul Sultan, of the Division of Epidemiology and Public Health at the University of Nottingham in the United Kingdom, aimed to understand which women might be at risk for developing blood clots during pregnancy.
Approximately 100 to 200 pregnant women out of every 100,000 develop a blood clot each year, according to background information in the study.
The researchers investigated 375,154 pregnancies in women aged 15 to 44 over a 14-year period. The pregnancies included both live births and stillbirths.
Then the researchers looked at the rate of blood clots occurring in the women either before giving birth or after giving birth and looked for common risk factors in the women who had blood clots.
The researchers found that women were at a higher risk for getting a blood clot while pregnant if they had varicose veins, inflammatory bowel disease, a urinary tract infection or diabetes (before becoming pregnant).
Among women with one of these risk factors, about 139 women out of 100,000 would be expected to develop a blood clot each year.
The women at the highest risk for developing a blood clot after birth were those who had had a stillbirth. Approximately 2,444 women out of every 100,000 who had a stillbirth would be expected to develop a blood clot each year.
After stillbirth, the risk factors associated with developing blood clots after giving birth were having varicose veins, inflammatory bowel disease, cardiac disease or a body mass index (BMI) over 30, which indicates obesity. BMI is a ratio of a person's height to weight and is used to determine whether someone has a healthy weight.
Approximately 637 women out of 100,000 who have one of these conditions or had certain pregnancy complications would be expected to develop a blood clot after giving birth. The pregnancy complications found to be risk factors were hemorrhaging during birth, a preterm delivery or a cesarean section.
The researchers concluded that their study "provides valuable information to clinicians for better decision making in terms of identifying high risk pregnant and postpartum women who may require some form of thromboprophylaxis."
Thromboprophylaxis refers to preventative measures to reduce the risk of developing a blood clot, such as injections of the blood thinner heparin.
Patients whose doctors are considering the use of thromboprophylaxis should discuss the risks and benefits of the intervention with their doctor.
The study was published April 2 in the journal Blood. No external funding was used for the research. One author was a co-developer of the guidelines related to blood clot preventive devices and has received speakers' fees from Leo Pharma and Sanofi Aventis, which both make devices used for blood clots during pregnancy.