The uterus is the principal organ involved in pregnancy and childbirth. Your child is conceived in one of its Fallopian tubes, implanted within its cavity and, at the appropriate time, is expelled by it through your vagina into the outside world.
During the forty weeks of pregnancy, your uterus increases in size to about 12ins. × 9ins. × 9ins. Its weight increases from 100 grams to 1,000 grams at full term and the amount of fluid it contains grows from a quarter of a teaspoon to approximately 1½ pints.
During the first sixteen weeks of pregnancy, the expansion of your uterus is caused almost entirely by the growth of its tissues owing to hormonal stimulation. The uterus becomes a thick-walled organ, circular in shape and is protected and cradled by the bones of your pelvis. Around this time you will begin to feel the ‘quickening’ movements of your child within the womb.
From the twentieth week, growth almost ceases and the uterus then expands because the muscle fibres are stretched by the growing child. At the very end of pregnancy, the lower segment of the uterus stretches most which is why a low-lying placenta will tend to rise as the uterine walls lengthen at the base. The walls of the uterus become thinner and in the latter half of the pregnancy you can feel your child’s body quite easily from outside. Your uterus becomes more oval in shape and moves up into your abdomen as your child grows.
As it enlarges, its position changes. At 12 weeks the fundus is just above your pelvic inlet. At 16 weeks, its upper end is nearly halfway to your navel, which it reaches at the eighteenth week. At 36 weeks, the top part of your uterus is lying just below your diaphragm, at the level of the lower end of your breastbone. During the last few weeks it drops a little lower as your baby settles into position for birth.
Your uterus is a hollow muscular organ which consists of a network of muscle fibres and bundles running in all directions, longitudinal, oblique and circular.
During pregnancy your baby lies within the uterus connected from his navel by the umbilical cord to the placenta which is attached to the wall of your uterus and draws nourishment for your child from your bloodstream and, simultaneously, passes waste products back to you. The placenta usually implants in the upper segment of the uterus towards the back but variations within the norm sometimes occur. The umbilical cord is made up of three intertwined blood vessels, two veins carrying oxygenated blood from the placenta back to the baby and one artery which carries de-oxygenated blood from the baby to the placenta.
Your baby has an independent blood circulation system which flows all round the body through the umbilical cord to the placenta and back again. After the birth, when your baby is breathing independently, the placenta is no longer needed and will separate from the wall of the uterus and pass through the cervix. Your baby’s placenta is about one-third of the size of your baby and is lined by the membranes. It looks like a large piece of liver. If it is examined and spread out one can see that it is a network of blood vessels, rather like the roots of a tree.
A bag of membranes surrounds your baby, the placenta and cord and also contains approximately 1½ pints of amniotic fluid – the waters within which your baby lies. These waters protect your baby from shock or infection and are constantly being replenished by your body.
At full term, at the end of pregnancy, the main function of your uterus is to evacuate its contents. During labour the uterus will contract at regular intervals and gradually open up at its base (the cervix) to allow your baby to pass through. Once it has opened, it will contract powerfully to expel your baby and the placenta, the bag of membranes and all its contents. (Placenta and membranes are called the ‘after birth’.) In the hours and weeks after the birth, your uterus will continue to contract rhythmically, stimulated by hormones. Your baby sucking on the breast will stimulate the release of these contracting hormones. The uterus will gradually shrink back to its original shape and size and will expel all the blood-rich lining which was used to nourish your baby. By the end of the sixth week after birth, your uterus will be back to normal and will have completed its task.
The Pelvic Bones
Your pelvis is the part of your body most directly involved with giving birth. It is the bony passage through which your baby will pass as it is born. During pregnancy your body produces hormones which soften the joints in order to increase their flexibility and assist the birth of your child. By regularly practising the exercises recommended in the next chapter, you can make the most of this natural flexibility and be at your physical best for giving birth.
TRY THIS:
a. Kneel on the floor and explore your pelvis from the outside. Place your hands on your hips and find the illiac crests – two bony points at your sides – and follow their curved rim with your thumbs round to the back. Feel your pubic bone in front, your sacrum and coccyx at the back.
b. Sit on your hands and feel your two buttock bones.
c. Kneel, then lift up one foot so that you are half-kneeling and half-squatting. Explore your pubic arch. Feel its curve extending from your buttock bones under your pubic bone. Your baby’s head will pass under this arch as it is born.
Your pelvis is shaped internally like a curved funnel – exactly the right shape to accommodate your baby’s head as it passes through during labour. From above you can see the pelvic inlet in which your baby’s head will engage, ready to be born; and from underneath the outlet through which it passes at birth.
Your pelvis has 4 major joints
The pubic joint in front can open by as much as half an inch during labour to make room for your baby’s head.
The two sacro-illiac joints are at the back. These joints expand from side to side and also move in a pivot-like way to increase the area of the pelvic canal and adapt to the shape of the descending head of your baby, as it passes through the pelvic bones.
When you bend forward, as in squatting or kneeling, your sacrum and coccyx lift up and this opens and expands the pelvic outlet. When you bend backwards or recline, this has the effect of closing the pelvic outlet and narrowing the space by as much as 30 per cent. This is one of the reasons why reclining is the worst position to adopt for giving birth.
The sacro-coccygeal joint is between your coccyx and your sacrum. This joint loosens during pregnancy so that your coccyx moves out of the way as your baby is born.
The pelvic joints are held together by ligaments which are like strips of very strong elastic.
The sources of power of this part of your body are the muscles which are attached to the bones and bring about movement at the joints when they contract and relax. The pelvic muscles include the buttock muscles at the back which provide strength and support for your spine and upper body, and are especially important during pregnancy. At