Threatened miscarriage, as demonstrated by vaginal bleeding with or without abdominal cramps, is a common complication of pregnancy. It occurs in about 20% of recognised pregnancies. Risk of miscarriage is increased in older women and those with a history of miscarriage. Low serum levels of progesterone or human chorionic gonadotrophin (hCG) are a risk factor for miscarriage. Other risk factors include heavy bleeding, early gestational age and an empty gestational sac of >15-17 mm diameter. Clinical history and examination, maternal serum biochemistry and ultrasound findings provide valuable information about the prognosis and are important to establish in order to determine potential treatment options. Although bed rest is the most common choice of treatment, there is little evidence of its value. Other options include luteal support with progesterone, dydrogesterone or hCG. There is some evidence from clinical studies indicating that progesterone or dydrogesterone may reduce the rate of miscarriage, although further data from double-blind, randomised-controlled trials are necessary to confirm efficacy.