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The First Trimester: Your Baby’s Growth & Development

First-Trimester-pregancy-test coping with morning sickness
Congratulations, Mama! This is such an exciting time as you navigate your first trimester.

Congratulations, Mama! Welcome to your FIRST TRIMESTER. This is early pregnancy and it is a crazy, wild time. It’s also the most crucial trimester for your baby’s development. Over these first three months, your baby grows from a tiny poppy seed into a mini human with a beating heart, fully formed organs and body. In the first trimester, babies even grow tiny little fingers and toes. It’s pretty incredible that our bodies provide the perfect space for our babies to develop that dramatically over such a short space of time.

It’s no wonder that all this hard work can start to take a toll on us physically as well – with morning sickness, next-level fatigue and low energy very common.

Let’s explore some of the phenomenal development your baby goes through over the first trimester!


The First Trimester: Your baby’s early pregnancy development

  • Your baby’s development begins as soon as sperm meets egg – a ball of rapidly dividing cells that makes its way from your fallopian tube to your uterus where it implants and will stay for the rest of your pregnancy.
  • By around week 5-6, your baby’s heart will start beating (yes, THAT early!). This may be able to be detected via vaginal ultrasound.
  • External genital organs develop. Although your baby’s sex can generally not be determined via ultrasound until you’re further into your second trimester.
  • Your baby’s arms and legs are fully formed. They have tiny little fingers and toenails starting to appear.
  • Your baby’s skeleton is forming, with most bones beginning as cartilage which hardens into bone.
  • Tooth buds are developing in your baby’s gums. These will become your little one’s teeth which will gradually emerge over their first year earth-side.
  • Eyelids are formed and your little one’s larynx (voice box) is also developing.
  • Reproductive organs are developing. The circulatory and urinary systems are functioning.
  • By the end of the first trimester, your bub can open and close their fists and mouth. Your little one is even able to suck on their thumb by this point.
  • Even though you can’t feel it yet, your baby’s movement is increasing all the time!
  • By the end of the first trimester, your baby (a “fetus”) is fully formed and is around 3-4 inches long and weighs ~28g.

If you’re still struggling with morning sickness and nausea at the end of your first trimester, please rest assured that this usually fades away by week 16-20. Not much longer, Mama!

Now that your baby has undergone the crucial development of the first trimester, the risk of miscarriage significantly drops.

Let’s dive into the second trimester and see what happens next!

Pregnant Mamas make sure you check out our FREE Prenatal class that 8 out of 10 new mothers say they wish they took before birth to ease their stress and worries. You can even watch it at your own pace from the comforts of your own home! Sign up here

It’s important to note that your pregnancy should be discussed with a healthcare provider to ensure safety and suitability for individual circumstances. This blog is general education only. For any personal based advice regarding you or your baby please seek advice from your own healthcare professional.

  1. Department of Health & Human Services. (02-2012). Pregnancy - week by week. Better Health Channel.
  2. Fetal development: The 1st trimester. (2022, June 3). Mayo Clinic.
  3. How your fetus grows during pregnancy. (December, 2021). ACOG.
  4. Professional, C. C. M. (March 3, 2023). Fetal development. Cleveland Clinic.
  5. Stages of pregnancy | Office on Women’s Health. (February 22, 2021).