Pregnant mom holding stomach with husband

You’re pregnant - congratulations! You’re about to become a mother. You might be curious as to how your baby will grow and develop during the course of your pregnancy. Read on to find out about fetal development and some other important points on what to expect during your first trimester.

What is the First Trimester?
The duration of a pregnancy is usually around 9 months1. Most doctors and health professionals divide this further into three periods or trimesters. Each trimester marks a specific fetal development2. While conception is the beginning of pregnancy, we count the first trimester of pregnancy from the first day of your last period until the 12th week of pregnancy. Health professionals and doctors do this because it is difficult to pinpoint the exact moment of conception.

Fetal Development in the First Trimester
You will see the most substantial fetal development occur during the first trimester3. For most of the first semester, the baby is still an embryo. As the semester ends, it goes from an embryo to a fully developed fetus. 
Here’s how your baby develops week by week3 4 5 6.

Weeks 1-3:
As stated above, we begin counting the start of pregnancy on the last day of your period. This means in the first two weeks, you aren’t technically pregnant yet. During these two weeks your body is preparing for ovulation. During ovulation, if a sperm manages to fertilize your egg cells, then pregnancy officially begins. Thereafter, the fertilized egg travels through the fallopian tube and fits its way to the womb. In a process called implantation, the fertilized egg borrows into the lining of the womb.

Week 4:
The embryo during the 4th week onwards to the 5th will grow and attach onto the lining of the womb. The embryo will establish a link with your blood supply for nourishment and will form layers within itself. These layers will eventually grow to be the different parts of your child’s body.
To summarize, these layers will eventually become your baby’s nervous, respiratory, circulatory and digestive systems, blood vessels, muscles, bones and brain. The development of these organs and muscles begins as early as the fourth week. Note that it is also around this time when the pregnancy test turns out positive.

Week 5:
Continuing from the fourth week, your baby is developing its nervous system along with the foundations for the major organs. At this time, your baby already has some blood vessels and blood is already circulating within them.
It is advised to take folic acid as early as the 5th week to prevent defects from occurring such as spina bifida. 

Week 6:
At six weeks of fetal development, there's already a noticeable bulge where the heart is, as well as a bump where the brain and head will eventually be. An ultrasound can already detect your baby’s heartbeat as early as the 6th week. You can also notice arms and legs are starting to form along with markings of where the eyes and ears will be. 

Week 7:
Following the developments of the 6th week, the brain is now developing rapidly at week 7. This causes the head to grow faster compared to the other body parts. The eyes and ears will continue to develop as well. For the other parts of the body, the limb buds where the legs and arms should be are starting to form cartilage which will eventually grow into bones. 

Week 8:
By week 8 the embryo is called the fetus. The limbs are continuing to grow longer. Placenta will be developing, forming structures that will attach the placenta to the womb’s wall.

Week 9:
At the 9th week of fetal development, the face is starting to form. Along with the face, the hands and feet are also continuing their growth. Organs such as the heart, brain, lungs, kidneys, and gut continue to grow as well.

Week 10:
The heart is now fully formed. This is also when your baby will make small movements that you can notice in the ultrasound.

Week 11:
At the 11th week of fetal development, the facial bones are fully formed. At this time, your baby’s head makes up a third of its length. The body will start developing faster and will soon catch up.

Week 12:
Your baby’s organs, muscles, limbs, and bones will be in place by now. Though your baby is moving as early as the 12th week, it’s still too early to feel these movements. 

What to Expect:
Along with fetal development, you should also expect some changes to your body to accommodate the life forming inside you. Here are some physical changes to expect5:

  • Tender swollen breasts
  • Nausea that might be accompanied by vomiting
  • Frequent urination
  • Fatigue
  • Food Cravings
  • Heartburn
  • Bloatedness
  • Constipation

Remember to communicate with your doctor or health care worker to ensure a healthy and successful pregnancy.

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1 First trimester ( 2020 ) retrieved September 1, 2020 from
2 Pregnancy the Three Trimesters ( n.d. ) retrieved September 1, 2020 from
3 The First Trimester ( n.d. ) retrieved September 1, 2020 from
4 Your Pregnancy Week by Week ( 2018 ) retrieved September 1, 2020 from
5 Fetal Development: The First Trimester ( 2020 ) retrieved September 1, 2020 from
6 Stages of Pregnancy ( 2019 ) retrieved September 1, 2020 from