twenty weeks - it is impossible to tell by the scan findings whether the baby will be small, average-sized or large. In fact, at this stage, fetuses of the same gestational age will be quite similar in size. Those destined to be big by their genetic inheritance will start pulling away from the pack in the third trimester. Trying to determine the gestational age accurately using an ultrasound scan in the third trimester is a futile exercise. The best you can hope for is a very rough guide.

What of the mother's tummy?
Examination of the abdomen in the first and second trimester is pretty accurate in determining the gestational age as long as the examiner knows what he or she is looking for. This also depends on things being normal with a singleton pregnancy. It is pretty useless in this respect for multiple pregnancy. Of course, examination of the abdomen is still valid for all the other purposes, even in multiple pregnancy.

For most of the first trimester, the womb is inside the pelvic cavity and abdominal examination will be negative. This is until near the end of the first trimester. In fact, the fundus (top) of the uterus just emerges at the bikini-line level at twelve weeks.
It is not uncommon to see a celebrity photographed showing an apparent "three-months bump". There is nothing like a three-month bump, unless the lucky mother-to-be is carrying triplets.

The fetus continues to increase in size and the various organs are maturing functionally. The amount of water (amniotic fluid) is also increasing. It follows that the     

fundus of the uterus will continue rising and therefore the belly grows bigger. The womb's ability to increase in size and accommodate the weight of its contents is quite amazing. At conception, the uterus is about the size of a small fist, weighing about 50 g. By the end of the third trimester, it will extend from inside the pelvis to the diaphragm beneath the ribs, weighing about 1000 g - twenty times its original weight, and that is minus its contents!
In a few weeks after delivery, the uterus will shrink back to its original size, or very close to it.

Contractions
Braxton-Hicks contractions are common and could start as early as the middle of the second trimester. A person examining the abdomen may feel these, but the mother is mostly unaware of them. She may start feeling them in the third trimester. They are usually irregular, unpredictable, short-lived and painless. The frequency may increase towards the end of pregnancy, to the extent of causing anxiety of impending labour. If one is unlucky, this stage may last three or four weeks, a grim prospect. Fortunately, this is unusual.

This is where a lot of people tie themselves in a twist. What does a phrase like "a baby born two weeks premature" mean? In fact, it doesn't mean anything!

"Term" is a period stretching a good five weeks. Once a pregnancy reaches thirty-seven completed weeks, it is already term. A week or four weeks later, if the baby hasn't arrived yet, it will still be "term" and