The New England Journal of Medicine as well as The Reuters Health Information Service both question reports in recent years regarding the use of aspirin in regards of preventing preeclampsia and high blood pressure. Preeclampsia is a major concern with doctors and the exact cause is not yet known.
Preeclampsia is defined as hypertension and protein in the urine or swelling of the hands and feet after 20 weeks' gestation. In its severest form, preeclampsia can cause kidney failure, liver dysfunction, cardiac and pulmonary failure, seizures, and death. Preeclampsia is one of the leading causes of maternal death in the U.S. It can also lead to women having premature and low-birthweight babies, possibly causing an increase infant morbidity and mortality.
Taking aspirin while pregnant can increase a woman's risk of having her placenta separate from the uterine wall (placental abruption) which can cause fetal compromise and even death, so doctors are reluctant to give aspirin unless the benefits outweigh this risk.
Pregnant women should discuss their medical history with their obstetrician and/or midwife and seek a second opinion if they have a question about any medication which their physician is prescribing - including aspirin.