Antepartum bleeding, also known as antepartum haemorrhage (APH) or prepartum hemorrhage, is genital bleeding during pregnancy after the 24th week of pregnancy up to delivery.

It can be associated with reduced fetal birth weight. Use of aspirin before 16 weeks of pregnancy to prevent pre-eclampsia also appears effective at preventing antepartum bleeding.

In regard to treatment, it should be considered a medical emergency (regardless of whether there is pain), as if it is left untreated it can lead to death of the mother or baby.

The total amount of blood loss and signs of circulatory shock due to blood determine the severity of the antepartum haemorrhaging. There are 4 degrees of antepartum haemorrhaging:

Placenta praevia refers to when the placenta of a growing foetus is attached abnormally low within the uterus. Intermittent antepartum haemorrhaging occurs in 72% of women living with placenta praevia. The severity of a patient's placenta praevia depends on the location of placental attachment;

Types 1 and 2 are classified as minor placental praevia as these typically result in minor antepartum haemorrhaging. Types 3 and 4 are referred to as major placental praevia due to the risk of heavy haemorrhaging in the case of a rupture due to the location of placental attachment. During the third trimester of pregnancy, thinning of the lower uterine segment or contractions caused by cervical dilation can increase the amount of stress placed on the placental attachment to the uterine wall. In patients with placenta praevia, these stresses can cause detachment of the placenta from the uterine wall causing haemorrhaging. To prevent further haemorrhaging patients with major placental praevia are recommended to have a caesarean delivery.

During pregnancy the layer of endometrium that attaches directly to developing blastocyst becomes the maternal portion of the placenta, also known as the decidua basalis. In the absence of a decidua basalis, trophoblast cells on the developing blastocyst form an abnormally deep attachment to the uterine wall, this is known as abnormal placentation. Abnormal placentation can categorised into 3 types, depending on the depth of infiltration of the chorionic villi into the uterine wall:

In placenta percreta, the chorionic villi have grow entirely through the myometrium and invade into the perimetrium. Placenta percreta results in the most intense haemorrhaging that can be expected caused by abnormal placentation. In the event of placental detachment from the uterine wall, the depth of chorionic villi attachment dictates the amount of haemorrhaging that can be expected. The chance of abnormal placentation increases in subsequent pregnancies, if there is scar tissue present from previous pregnancies. For example, previously undergoing a caesarean or placenta previa increases the likelihood of abnormal placentation, therefore increasing the chances of antepartum haemorrhaging.