Top The First Trimester Pregnancy resources

A three-part series on the trimesters of pregnancy for both Mummy and the unborn Baby

The human gestation period is divided into trimesters - three periods of three months. The entire gestation period lasts around 40 weeks. This first article outlines basic information you may find useful about the first trimester which covers the initial 12 weeks after the first day of your last menstrual period.

Mummy's body

Physical changes:
It is not your belly but your breasts that will start changing in appearance. You are likely to notice that your bra feels tighter. Your belly is unlikely to show a bump until after your fourth month of pregnancy.

You may also gain weight during the first trimester although some mummies-to-be actually lose weight because of morning sickness. The average weight gain by the end of the first three months is around 2.5kg.

Pregnancy Symptoms:
You may start experiencing common pregnancy symptoms such as morning sickness (nausea), dizziness, headaches, a frequent urge to urinate, heart burn and food cravings. These symptoms can kick in from about the time you miss your period and they are caused by hormonal changes in your body.

Emotional Changes:
Raging hormones may also cause some mummies-to-be to feel irritable and have constant mood swings. It is common to have a wide range of feelings about the pregnancy including fear, joy, apprehension and excitement, regardless of whether the pregnancy is planned.

Fetal Development

Weeks 1 to 3: Fertilisation and implantation
The fertilized egg attaches to the lining of your uterus and begins to grow and double in size every day. The placenta and umbilical cord start to form.

Weeks 4 to 6
This is when you miss your period. The embryo is around 1/100 inch (around 0.25mm) long by Week 4 and it now has a spinal cord. By Week 6, the embryo grows to around 1/6 inch (around 4.23mm) long. Your baby's heart is now beating. Limb buds, which will become the baby's arms and legs, begin to form and blood circulation begins.

Second Month
The embryo is now about inch (12.7mm) long. This is when the baby's development is very rapid. By the end of the second month, all the major body organs and body systems have begun to develop. By the end of the month, your baby already looks like a tiny infant.

Third Month
The baby begins to move its arms and legs and it can already open and close its mouth. Hair is beginning to form on the head. Fingers and toes are now distinct. By the end of the first trimester, the baby is about 2.5 inches (63.5mm) long.