Fetal development in the first trimester

Expectant parent with picture of ultrasound. Early pregnancy. 1st 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?


Highlights of Development


The 40 weeks in pregnancy are counted from the first day of your last period fetal development 1 month


An egg matures in one ovary and is released


The mature egg is fertilized by sperm


Implantation is complete by the end of this week

You will miss your period


The spinal cord and nervous system is developing fetal development 2 months


Eyes, ears, nose and the digestive system start to form

The heart starts to beat


Arms and legs start to form


The mouth is more developed and baby teeth are starting to form


Fingers and toes are growing fetal development 3 months


External genitals are starting to form


Your baby is kicking and moving around in your uterus


Lungs, stomach and intestines are taking shape


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.

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