Thursday, 28 February 2013

Post partum haemorrhage

Maternal mortality rates Wikimedia Commons

In developing countries, loss of blood after childbirth is a major cause of death. The bleeding occurs from blood vessels that rupture when the placenta detaches from the uterine wall. Usually the vessels are closed by a strong contraction of the uterine musculature. Occasionally that mechanism fails.

Recently Elizabeth Abrams and Julienne Rutherford asked what was known about birth in non-human primates. Maternal death from post partum bleeding seemed nowhere near as common as in humans. Why?

Although widening of the uterine arteries does occur in pregnant monkeys, the process extends much deeper in the human uterus. The advantage to humans is that it ensures a greater supply of oxygen to aid development of the fetal brain. Abrams and Rutherford suggested that this advance came with a price tag that included a bigger risk of post partum blood loss.

Guinea pigs mate after giving birth

Pregnant guinea pig Wikimedia Commons

More than a century ago, Hans Strahl understood the importance of studying what happened to the uterus immediately after birth. He noted that guinea pigs and many other rodents mate soon after giving birth. In these species the placenta detaches with minimal damage to the uterus. It can be repaired quickly enough to receive the new embryo as it implants a few days later.

Elephants space their pregnancies

African forest elephant Wikimedia Commons

This is by no means universal. One of the best documented instances is the African elephant. After birth there is extensive bleeding into the uterine cavity. Loosening of the placenta leaves a permanent scar – at autopsy the number of scars in the uterus indicates how often an elephant has been pregnant. However, the interval between pregnancies is 6-8 years so there is more than enough time for the wound to heal. For more on elephant placentation follow this link.

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