Congratulations, your journey to motherhood is underway! With the first realization that you're having a baby, together with uncomfortable morning sickness and erratic mood swings, your 1st trimester is a very exciting yet overwhelming stage of your pregnancy. Find out other changes to expect during this stage of pregnancy.

First Trimester: Week 0-13

Your Baby's Growth and Development

Your baby's growth rate is the most rapid during the 1st trimester. In fact, the 1st trimester is also one of the most crucial stages for your baby. It is during this period that the baby is most vulnerable to damage from drugs taken by the mother, or infections, like German measles, affecting the mother.

Week 4: The embryo's spinal column, nerves, some blood vessel and the heart have started to form.

Week 5: First heartbeats begin. Arm and leg buds appear.

Week 6: Nostrils are formed. Brain and instestines grow.

Week 7: Fingers and feet start to develop. Ears, eyes and nose appear. Teeth begin to develop beneath the gums.

Week 8: Body grows. Cartilage and bones begin to form. Webbed fingers and toes appear.

Week 9: Most basic development is complete and all major body systems have formed.

Week 13: The baby's sexual organs develop.

By the end of the 1st trimester, the baby is about 3.4" long and weighs about 43 grams.