The third stage of labor is an unpredictable time. It ought to be a period of rest and rejoicing after the birth of the baby if all has gone well so far, but in thousands of women it can become very dangerous.
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This is because of the many complications that may occur during the third stage. The active management of the third stage is one approach which evolved in to prevent these complications in as many women as possible.
The conditions which often complicate the smooth course of the third stage include the following:
Postpartum hemorrhage (PPH)
When the third stage of labor is prolonged beyond 20-24 minutes (as opposed to the 30 minutes that was the earlier benchmark), it may be a risk factor for postpartum hemorrhage (PPH) which kills more than 1.25 million women a year.
Even when it doesn’t take maternal life, it causes excessive blood loss (over half a liter of blood) following childbirth in a staggering 14 million cases. Most of this bleeding comes from the placental site, which fails to contract properly.
Typically, natural figure-of-8 muscular fiber loops are present around the blood vessels, so that the torn vessels are quickly closed off after the placenta separates and the uterus contracts. PPH is particularly deadly because two out of every three women who develop PPH had no preceding risk factors before delivery.
PPH may also be associated with the following conditions which are also associated with an abnormal third stage. An anemic mother is at higher risk of PPH because clotting is more difficult and because even a relatively small blood loss may precipitate signs and symptoms of hypovolemia due to the initial lack of blood.
The retention of part or the whole of the placenta, including the membranes, for over 30 minutes after the delivery of the baby, is called retained placenta. It has several causes:
- Premature closure of the cervix so that the separated placenta is trapped inside the uterine cavity
- A full urinary bladder which prevents the placenta from passing through the birth canal by its pressure
- Retention of a part of the membranes or placenta after placental expulsion
The last three conditions may also lead to uterine atony resulting in PPH, because the uterus cannot contract well with the placenta inside it.
Atonic or flabby uterus:
In some women, the uterus doesn’t contract strongly enough to separate or expel the placenta completely. As mentioned above, a flabby uterus may be associated with a retained placenta, but also with conditions such as:
- Placenta previa or implantation of the placenta in the lower part of the uterus, which means the muscle fibers are weakened by the infiltration of blood vessels and placental tissue between them. This leads to weak contractions after the delivery.
- Placental abruption or premature separation of the placenta before the child is born
- Multiparity: A woman who has already carried more than five pregnancies can have an atonic uterus and PPH.
- Multiple pregnancy: If a woman is carrying twins or higher order pregnancies, the abdomen and uterus are highly distended. The stretched uterine muscle fibers may be unable to contract properly immediately after delivery and this leads to atony.
- Polyhydramnios: This refers to the presence of excessive (over 3L) amniotic fluid inside the uterus, which causes overstretching and subsequent atony of the uterine muscle in many cases
- Large fetus: A woman carrying a large baby (weighing 4 kg or more) also has the potential for uterine atony because the muscles are weakened by the overstretching.
- Prolonged labor and dehydration: If a woman is in labor for over 12 hours, it is more common to have uterine atony, perhaps because of muscular fatigue, dehydration and acidosis.
This is a rare but very serious complication of the third stage, slightly more common with controlled cord traction, in which the uterus is turned inside out and comes out through the vulval orifice wholly or partly.
To avoid this, a non-separated placenta should never be pulled out using this technique. Fundal support is also taught as a method of preventing uterine inversion, but not enough evidence exists as to its usefulness. Risk factors for uterine inversion include:
- Prolonged labor over 24 hours in duration
- Short umbilical cord
- Over-zealous cord traction
- Use of magnesium sulfate which relaxes muscles, during labor
- Placenta accrete when the placenta is firmly attached to the uterine muscle and cannot separate
- Congenital uterine anomalies