The most common cause of postpartum hypertension is high blood pressure stemming from gestational hypertension or pre-eclampsia that persists after delivery.
Pre-eclampsia refers to high blood pressure and excess protein in the urine after 20 weeks of pregnancy in a woman who previously had normal blood pressure.
Another cause of postpartum hypertension could be the "shifting" of fluids from the swollen tissues back to the arteries. This excess of fluids in the body's tissues can be a result of hormonal changes that occur in a woman after childbirth, from the administration of IV fluids during delivery, or from pain medication effects.
All cases of high blood pressure after delivery should be monitored closely so your doctor can determine the appropriate treatment.