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What Happens In Trimester 1?

Dr TC Tan | Published on January 29, 2023

In the first 12 weeks of your pregnancy, you will notice changes to your body, many of them early pregnancy symptoms prompting you to take steps to confirm your pregnancy. Inside you, something magical is happening — a single-celled zygote grows and develops into an identifiable human form.

What Will I Experience?

The first thing you probably notice is a missed period, which may prompt you to take a pregnancy test. You may also observe other early pregnancy symptoms such as:

  • Tender breasts
  • Light spotting (due to implantation)
  • Thin white discharge
  • Fatigue
  • Mood swings
  • Morning sickness
  • Food cravings
  • Constipation
  • Frequent urination
  • Heartburn
  • Slight weight loss

Pregnant women will experience some or all of the above to a varying degree. But if you notice severe abdominal pain or bleeding, see your doctor immediately.

Watch this video below for the Top 6 Common pregnancy symptoms in First Trimester

What Will Happen To My Baby?

Weeks 1–3

During the first 2 weeks of your pregnancy, you’re actually not pregnant — Day 1 of your journey is actually the first day of your last menstrual period. Around 2 weeks later, you ovulate and your partner’s sperm fertilises your egg. The fertilised egg then moves slowly along the fallopian tube towards the uterus, where it will be implanted into the lining of the uterus.

Read more about what happens in Weeks 1, 2 and 3.

Weeks 4–6

The embryo grows rapidly — the foundation of the brain, lungs, nervous system and other major organs begin to appear. At the same time, the placenta begins to form, getting ready to provide nutrients and oxygen to the embryo through a developing umbilical cord. Around this time, you probably notice you’ve missed your period and if you undergo a vaginal ultrasound scan, you may see your baby’s heart beating.

Read more about what happens in Weeks 4, 5 and 6.

Weeks 7–8

The embryo develops into a foetus, with a more distinguishable head, body and limbs. The brain is developing fast, along with the spinal cord. The placenta is still in development at this stage.

Read more about what happens in Weeks 7 and 8.

Weeks 9–10

Your developing baby’s facial features are more obvious — you may now be able to identify the eyes, nose and mouth. The limbs continue to develop and fingers and toes begin to form. The heart is fully functional at this stage. Although you cannot feel the baby move just yet, ultrasound scans will be able to capture small movements of the foetus.

Read more about what happens in Weeks 9 and 10.

Weeks 11–12

The head of the foetus is still proportionally big but the body is rapidly developing. Their sex organs have also developed, but it may be difficult to decipher if your baby is a girl or boy at this stage. By the end of the first trimester, all major organ systems have formed and the placenta is fully developed, ready to supply the foetus with what it needs to mature into a tiny human.

Read more about what happens in Weeks 11 and 12.

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