The first trimester of pregnancy - online guide

Although your first trimester of pregnancy sees few outward changes to the body, enormous changes are taking place inside you. The first trimester of pregnancy is the most critical time in terms of your baby's development as all internal organs and systems develop during this time.

Please note that pregnancy is dated from the first date of your last period and so your baby is actually two weeks younger than the recorded number of weeks of pregnancy. For example at three weeks of pregnancy your baby is only one week old.

By week five of your pregnancy (when the baby is three weeks old and one week after your missed period) the head becomes discernable from the rest of the body and traces of eyes and ears can be seen. At this stage key organs such as the liver and kidneys begin to develop, and muscle and bone are beginning to form.

In week six growth is very rapid. Although the baby may still look like a tadpole it has a brain and a tiny heart which beats independently of its mother. The baby has also developed its own bloodstream. The digestive tract, abdominal and chest cavities, and backbone begin to develop this week. Tiny buds appear on the body and will later become arms and legs. At this stage you may feel very tired and experience the first bouts of morning sickness .

By week seven nostrils begin to develop, and rudimentary hands and feet can be seen. The heart has now divided into two chambers, and is beating at 150 beats a minute, twice the adult rate. At this stage it is possible to measure the baby's length, which gives an accurate indication of the baby's age and therefore your due date. It's common to feel faint or dizzy at this time in your pregnancy due to changes in blood pressure.

By week eight bone cells begin to harden and lengthen and the joints start to form. Facial features continue to develop and the baby grows. Between week eight and week 12 you'll go for your first antenatal visit.

In week nine the baby starts to look like a real baby, limbs continue to grow and fingers and toes are now almost complete. The nose has formed and the uterus has doubled in size. Hormonal changes to your body will cause you to feel emotional and easily irritated and you'll notice a need to urinate more often.

By week ten the embryo has become a fetus with most joints formed. The genitals begin to form but it is too early yet to tell the gender of the baby. By now the heart is almost completely developed and other internal organs begin to function. The lungs, stomach and intestine continue to develop.

By week 11 the baby is out of the critical stage of development and is less likely to develop any congenital abnormality after this date. This week the irises start to develop, and fingernails and hair begin to appear. By now the baby can yawn, suck and swallow.

By week 12 the baby is fully formed. Although the organs, and particularly the brain, will continue to develop, fingers and toes have separated and hair and nails are growing. Symptoms of morning sickness will start to subside and you should feel less tired.

Although the baby is fully formed, at week 13 it still could not survive outside the uterus as the lungs and other organs are not yet fully functional. By this stage the baby has a fully-formed neck that can support head movements, and the ears and eyes are moving into normal positions. Although the ears are not yet fully formed, health professionals agree that babies can start to sense sounds at this stage - it is thought that this happens through vibrator receptors on the skin. Your baby is strong and well developed at this stage and after this first trimester of pregnancy the risk of miscarriage drops by 65 percent.

© The Pink Fridge Online Magazine 2008 - The First Trimester of Pregnancy