There are many stages in pregnancy when a woman's stomach will get hard. Which stages this happens at will totally depend on what shape and size the woman is and how she is carrying the weight of the unborn child.
In the early stages of pregnancy, usually between six and ten weeks. The uterus will harden. At this stage it will be very low and near the pubic bone. If the mother is slender in this area, the hardening of the uterus will become noticeable. This hardening should only be the size of a clementine and will be the baby, uterus and all of the fluids inside to keep the unborn child alive.
During the second trimester, usually around weeks 12 - 16, the uterus starts to move upwards and will sit between the pubic bone and the belly button of the mother. This will be stretching in size and will be expanding. As this moves the stomach area will harden and the bump of the baby in the stomach will start to show.
Around week 21 which is at the end of the second trimester, the unborn child will be developing very quickly. One of the changes that happens during this week is that the skeleton, although this has been there for many weeks, will start to become harder and will become more solid. This is said to increase how hard the mother's stomach is and adds to the size of the baby bump significantly.
On and off throughout the pregnancy, the mother will retain water in different areas and for different reasons. This may be due to hormones or could be due to the temperature outside or what she has eaten or drank. This can have an affect on how hard the stomach feels. This can make it hard one day and a little softer on other days and is completely normal.
