Placental abruption refers to the premature separation of the whole or part of a placenta which is implanted in the upper two-thirds of the uterus. Normally the placenta only separates from the uterus after the delivery of the fetus, in the third stage of labour (you will learn all about this in the module on Labour and Delivery Care). The mother and the baby may die if the place where the placenta pulled away from the wall of the uterus starts to bleed a lot.
Why is it likely that placental abruption will result in a lot of bleeding, and why does this pose a serious risk to the mother and the fetus? (Think back to what you learned about the structure of the placenta in Study Session 5, or look again at Figure 5.5 in Antenatal Care, Part 1.)
The mother's blood flows into large spaces in the placenta which lie close to the fetal blood vessels (Figure 5.5). If the placenta tears away from the wall of the uterus, the mother's blood will flow out into the cavity of the uterus and she could die from the loss of blood. The supply of oxygen and nutrients from her blood to the fetus will be reduced, so it may die or be severely brain damaged.
Most of the bleeding from the place where the placenta has pulled away from the wall of the uterus may escape through the cervix and flow out of the vagina. This blood is usually dark in colour because it doesn't contain much oxygen. This is an important warning sign!
However, in some cases, all the blood from the detachment site may stay inside the uterus cavity, which begins to fill up with blood (Figure 21.1). You will not see external bleeding, as very little of the blood escapes through the vagina. However, the woman will show the typical signs of severe internal bleeding known as haemorrhagic shock, which we already described briefly in Study Session 20 on early pregnancy bleeding. We repeat the information below (Section 21.2.1) because there is even more risk of it happening when a woman bleeds late in the pregnancy.
Other signs of placental abruption include:
- If the mother is already in labour, notice if she has pain between contractions, which may get worse and worse as time passes
- Her abdomen is hard, sore and tender to the touch
- The baby's heartbeat can be very fast (faster than 180 beats a minute), or very slow (slower than 100 beats a minute), or if you cannot hear a fetal heartbeat the baby could be dead
- The baby moves less or not at all.