Many causes for blood loss
There are many possible causes of massive blood loss during delivery.
Among them are low-lying placenta, abruptio placenta, blood disorders and pre-existing fibroids, said Dr Lee Keen Whye.
The consultant obstetrician and gynaecologist at Singapore O&G said that failure of the uterus to contract could also cause excessive bleeding.
He said: "Sometimes if the bleeding is bad, it can cause danger to the baby and mother."
In abruptio placenta, the placenta separates from the uterus before the baby is delivered. The cause is usually hard to determine.
Tears during delivery, such as those in the vagina, cervix and uterus, could also cause heavy bleeding, said Dr Wee Horng Yen.
The senior consultant obstetrician and gynaecologist at Novena Medical Centre said: "When this occurs, bleeding is brisk. Bleeding is particularly heavy if an artery is torn.
"The longer and deeper tears are associated with heavier blood loss. A tear may extend into the rectum and anus."
He said that large babies, the abnormal position of a baby's head during birth and high rotational forceps to turn a baby's head could cause tears.
HARDER TO REACH
When there are multiple and deeper tears, there may be more bleeding as it is hard to reach "a small area that is bleeding from multiple points", Dr Wee said.
Multiple bleeding points also obscure the anatomy, making it more difficult to stitch. Also, bleeding points are often near vital structures such as the ureter, bladder, rectum and anus, he said.
Dr Lee said that some of these complications are unpredictable and can happen out of the blue, such as amniotic fluid embolism.
He said: "Amniotic fluid embolism changes the clotting effect of blood in the mother, leading to blood loss from the uterus, open wounds, gut, bladder, brain and others.
"When the brain has less blood and oxygen, the patient goes into coma."
Rare but deadly, it affects 0.1 per cent of pregnant women - or one in 1,000.
The New Paper reported last October that a woman survived amniotic fluid embolism after receiving 37 bags of blood products from the Singapore Red Cross Society.
The medical team successfully compressed her womb and stitched up the episiotomy - a surgical cut in the muscular area between the vagina and the anus - in a five-hour operation.
After the operation in July 2012, the woman recovered.