Fetal development in the first trimester

Follow this 3 part series to learn about your baby’s development throughout your first, second, and third trimester.

What do I need to know?

The early part of pregnancy, also called the first trimester is about 3 months long. It is an important time in pregnancy for your baby’s growth and development because all important structures and organs begin to develop during these first weeks.  Although it’s important to seek health care, eat well, be active and stay away from harmful environmental exposures before and throughout your pregnancy, it’s especially important during this time.

What’s happening and when?

Week	Highlights of Development
1	The 40 weeks in pregnancy are counted from the first day of your last period
2	An egg matures in one ovary and is released
3	The mature egg is fertilized by sperm
4	Implantation is complete by the end of this week You will miss your period
5	The spinal cord and nervous system is developing
6	Eyes, ears, nose and the digestive system start to form The heart starts to beat
7	Arms and legs start to form
8	The mouth is more developed and baby teeth are starting to form
9	Fingers and toes are growing
10	External genitals are starting to form
11	Your baby is kicking and moving around in your uterus
12	Lungs, stomach and intestines are taking shape
13	Fingernails and toenails are forming The heart is completely formed

By the end of your first trimester, your baby is approximately 7.5 cm long and weighs 30g.

If you have any questions or concerns about your baby’s development, be sure to speak with your health care provider.  Next up is your baby’s development in the second trimester.