Your uterus: 10 amazing facts
The increase in size, weight and volume of the uterus during pregnancy is phenomenal. It grows from non-pregnant to pregnant at term like this: Size: 7.5cm x 5cm x 2.5cm to 30cm x 23cm x 20cm Weight: 50g-60g to 900g-1 000g Volume: 6ml-5 000ml (holding capacity of the cavity)
The uterine muscle is the only muscle in the body that can contract and retract. This means that during a contraction, when the muscle shortens, it won’t lengthen to the same degree once the contraction has passed. This will continue until the muscle has “bunched up” at the top of the uterus. Once there, it gathers its strength to contract and expel the baby.
The walls of the uterus are made up of two distinct tissue layers and a third covering layer. All three layers are suited to maintaining pregnancy and then accomplishing labour and birth.
Within five days your amazing uterus has made a rapid recovery and is back where it started, at the beginning of your pregnancy. By day 14 it’s the same size as it was before you fell pregnant. The rest of your body takes a little longer to recover, however!
The uterus has an extremely rich blood supply in order to nourish the foetus during pregnancy. During late pregnancy up to one litre of blood per minute passes through the uterus.
The nerve supply to the uterus is complex and isn’t yet fully understood. The pain receptors respond loudly to a diminished supply of oxygen and to the sensation of stretching. As it’s necessary for the cervix to stretch in order to open, you’ll have to learn how to work with your body to ease the discomfort during labour. As far as the oxygen supply is concerned, you can understand why it’s so important for you to breathe through your contractions, be it with your natural breathing, or patterned breathing techniques.
Braxton-Hicks contractions are mild and irregular, but although they remain painless, they gradually increase in frequency and intensity as the pregnancy nears term. The uterine muscle tightens for about 30 to 60 seconds and then relaxes. These contractions facilitate blood and oxygen to the placenta and the growing baby. After 30 weeks they start to increase in intensity and are now thought to be brought about by the increase in the level of prostaglandins, and the fact that the uterine muscle becomes increasingly sensitive to oxytocin as labour approaches. These contractions prepare the uterus for labour.
During the first stage of labour it’s the function of the uterus to thin out and open up the cervix. During the second stage of labour it expels the baby, with voluntary effort from the mother. During the third stage of labour, the uterus has to contract tightly to peel the placenta off its walls and to squeeze down firmly so the amount of blood lost from the placental wound site is very little. This is where the living ligatures come into effect. As the uterus continues to contract and retract the many blood vessels are pinched and bleeding stops.
According to obstetrician and author Dr Gordon Bourne, it takes an average of 150 contractions to deliver a first baby, 75 for a second or third child, 50 for a fourth or fifth and 30 to 40 for subsequent children.
The uterus contracts painlessly all the way through pregnancy, but these contractions are usually only felt by the mother during the second half of the pregnancy.