The progressive change in the size of the uterus to accommodate pregnancy is one
of the wonders of nature. The uterus increases in weight almost 25 to 30 times. From
around 30-50g pre-conception, it grows to about 1000 g (1 kg) at term. While the
capacity of the uterine cavity when not pregnant is about 4-5ml, this is increased
almost a thousand-fold at term.
The tiny structure, smaller than a woman's fist, grows to accommodate a baby, placenta
and fluid with a combined weight of anything up to 8 kg or even more (such as in
The visible pregnancy ‘bump’
To the outside world, there is no tell-tale abdominal bulge before 12 weeks of gestation.
This is because, up until this point, the pregnancy is entirely within the pelvic
cavity. An exception is in the case of twins or other forms of multiple pregnancy,
where the bump may appear earlier.
Even in a singleton pregnancy, there may not be any visible distension before eighteen
to twenty weeks, depending on the woman's build. After this mid-way stage, the abdomen
actually distends and the increase in size is, in most cases, immediately apparent.
Size of the visible pregnancy bump
We have all witnessed the enormous difference of the sizes of pregnant abdomens.
Every individual woman appears to be different. A combination of factors is actually
The size of the bulge will depend on the size of the contents of the uterus (twins
will produce a bigger bulge at a comparable gestation) but this is not the only factor.
The state of the abdominal muscles and their ability to rein in the growing uterus
is also important.
Another factor is the amount of fat deposited under the skin on the abdominal wall.
This may be big enough to influence the outward impression of the size of the pregnant
Contrary to popular belief, the apparent size of a pregnant abdomen is actually a
poor guide to the size of the baby.