The entire process of pregnancy from conception to birth takes about nine months, or 40 weeks. The pregnancy is divided into three-month periods known as trimesters.

The First Trimester (Week 1 to Week 12)
The first three months of foetal development are, perhaps, the most important. During the first 60 days, most of the baby's organs are formed. It is at this stage that the unborn child is most sensitive to environmental chemicals, drugs and viruses that can cause birth defects.

The Second Trimester (Week 13 to Week 28)
During this time, the foetus begins to grow and its organs mature. The increasing size of the uterus becomes obvious in the second trimester of pregnancy, as the woman's belly begins to swell.  Many women need to start wearing loose or maternity clothes at this time.

The Third Semester (Week 29 to Week 40)
The third trimester begins at the 27th week of pregnancy and lasts until birth.  The baby continues to grow and put on weight throughout the last trimester of pregnancy.