top of page
  • Julie Bos

From Conception to Fully Formed - Your Baby’s Development in the First Trimester

From Conception to Fully Formed

Your Baby’s Development in the First Trimester

Your pregnancy test is positive! And so begins your first trimester of a nine-month-long journey to meeting your baby.

The first trimester of your pregnancy—from the start of your last menstrual period to 13 weeks—is marked by a rollercoaster of emotions and physical symptoms (thanks, pregnancy hormones).

But for your baby, those first few weeks are foundational to their overall development in the womb.

So what is actually happening to your baby, anyway?

Baby Development Highlights

Your pregnancy begins at conception, and soon after the embryo implants itself in your uterine wall, your baby’s development really takes off.

During the first three months of your pregnancy, your baby will grow more rapidly than at any other time during your baby’s life—from the size of a poppy seed to the size of a lemon!

Here are some highlights of your baby’s development in the first trimester:

· Heart: By week 5, a tube-like heart begins to beat and becomes more regular. By week 10, you’ll be able to hear a strong heartbeat at your first ultrasound. It won’t become a four-chamber heart until the second trimester.

· Brain: Your child’s brain, spinal cord, and nerves start out as one neural tube, but by 5 weeks, will become their own parts of an interrelated system.

· Bones: By week 6, your baby begins to sprout their limbs. Around week 10, your baby will even have their fingers with unique fingerprints and all their toes.

· Digestive System: Your baby’s digestive system, including intestines and urinary system, form and start its work by week 8.

· Senses: Your child’s optic nerves begin to develop around 4 weeks, and his or her eyes are fully formed by week 10. Between weeks 8 and 12, your baby will begin to develop their sense of touch and taste.

· Major Organs: By the end of your first trimester, your baby will have begun to develop their lungs, genitals, liver, and thyroid. These organs will continue to develop until your baby is born around 40 weeks.

Did you know? By the end of your first trimester, your baby is fully formed.

“For You created my inmost being; you knit me together in my mother’s womb. I praise you because I am fearfully and wonderfully made.” Psalm 139:13-14 (NIV)

With all these building blocks in place, your baby will get only bigger and bigger – and so will your belly.

At LivingWell Pregnancy Centers, we care about you and your growing baby. That’s why we offer free women’s wellness checkups, pregnancy tests, your first ultrasound, and endless education and resources.


bottom of page