Pregnancy Week by Week

The first trimester starts on the first day of your last period and runs through weeks 1 to 13 of pregnancy. During this time, your baby grows from a tiny cluster of cells to the size of a plum.

Pregnancy Week 1Preparing for conception

Pregnancy Week 2Ovulation

Pregnancy Week 3Egg fertilisation happens

Pregnancy Week 4Baby is growing inside you

Pregnancy Week 5Baby looks like a tadpole

Pregnancy Week 6Baby is size of a sesame seed

Pregnancy Week 7Baby's brain develops

Pregnancy Week 8Baby's hands appear

Pregnancy Week 9Baby responds to touch

Pregnancy Week 10Tongue is fully formed

Pregnancy Week 11Fingernails and hair appear

Pregnancy Week 12Baby can open it's mouth

Pregnancy Week 13Vocal cords form

The second trimester runs from week 14 to week 26 of pregnancy. If you found the first trimester hard going, this stage is often steadier, with more noticeable movements and time to prepare for your baby's arrival.

Pregnancy Week 14Baby practices using its lungs

Pregnancy Week 15Baby can make a fist

Pregnancy Week 16Baby reaches 100g in weight

Pregnancy Week 17Baby practices blinking

Pregnancy Week 18Bones begin to harden

Pregnancy Week 19Baby can hiccup!

Pregnancy Week 20Baby sleeps and wakes

Pregnancy Week 21Halfway there!

Pregnancy Week 22Baby responds to outside noise

Pregnancy Week 23Downy hair covers baby's body

Pregnancy Week 24You can hear baby's heartbeat

Pregnancy Week 25Baby may suck its thumb

Pregnancy Week 26Eyebrows and eyelashes appear

The third trimester starts at week 27 and continues until your baby arrives. Your baby grows quickly during these final weeks, while your body prepares for labour, birth, and the early days with your newborn.

Pregnancy Week 27Lungs capable of breathing air

Pregnancy Week 28Baby's eyelids open

Pregnancy Week 29Eyes prepare to see

Pregnancy Week 30Brain develops rapidly

Pregnancy Week 31Baby's growth begins to slow

Pregnancy Week 32Baby can use all 5 senses

Pregnancy Week 33Skin changes colour

Pregnancy Week 34Baby's eyes are blue

Pregnancy Week 35Baby preparing for birth

Pregnancy Week 36Finishing period

Pregnancy Week 37Baby turns towards light

Pregnancy Week 38Toenails reach end of toes

Pregnancy Week 39Baby gains fat ready for birth

Pregnancy Week 40Baby appears!

Understanding Pregnancy Trimesters

Pregnancy can be a little confusing when it comes to trimesters. You may wonder how many weeks are in each trimester and when they begin and end. Different websites sometimes show slightly different answers because there are a couple of common ways to count them.

Here is a quick breakdown of the two methods you will see most often:

• Gestation method (used here): This counts the full 40 weeks of pregnancy from the first day of your last period, including the two weeks before conception. In this method, the first trimester covers weeks 1 to 13, the second trimester weeks 14 to 26, and the third trimester weeks 27 to 40.
• Baby development method: This starts pregnancy at ovulation and skips the two weeks before conception, so some sources describe trimester changes slightly differently.

Both methods are widely used, so you may notice slight variations depending on the source. Whatever method you prefer, this guide is here to help you follow your baby's development week by week.