The second trimester (weeks 13 to 27) is an exciting time in your pregnancy, not just because symptoms like nausea often ease, but because your baby is growing at a rapid pace. In just 15 weeks, your baby will go from the size of a peach to as big as a cauliflower.
Understanding what’s happening week by week can help you feel more connected and confident as your pregnancy progresses. Here’s a detailed look at your baby’s development throughout the second trimester.
Weeks 13–16: Small but Mighty
By week 13, your baby is about 7.5cm long (the size of a peach) and weighs around 25g. Though still small, they’re growing fast:
- Bones are beginning to harden
- Facial features become more defined
- Vocal cords are forming
- Your baby can move arms and legs
By week 16, your baby is around 11.5cm and weighs about 100g. They may be sucking their thumb and making facial expressions like frowning or squinting.
Weeks 17–20: Feeling the First Flutters
From week 17, your baby is developing fat stores, and their heartbeat is strong enough to be heard with a Doppler.
By week 20:
- Your baby is about 25cm long (from head to heel) and weighs around 300g
- They’re covered in a protective white coating called vernix
- Eyebrows, eyelashes, and hair are growing
- Baby is starting to swallow and produce meconium (the first poo)
- Movements become stronger - you may feel gentle kicks or flutters
This is also when your anomaly scan happens, a detailed ultrasound that checks your baby’s organs and overall growth.
Weeks 21–24: Growing Muscles and Senses
Your baby continues to grow steadily in size and strength. By week 24, they measure around 30cm and weigh about 600g.
During these weeks:
- Taste buds develop, and your baby can taste flavours from the amniotic fluid
- They start responding to external sounds
- Lungs are forming branches and producing surfactant (a substance vital for breathing after birth)
- Sleep cycles begin, and baby may startle from loud noises
This is also when your baby’s kicks become more consistent and easier to recognize.
As your baby grows so does your stomach, and with that can cause itchy, dry skin. Try our Cooling Serum to ease any itchiness.
Weeks 25–27: Ready for the Final Stretch
By the end of the second trimester, your baby will weigh close to 1kg and be about 34–36cm long. Their body is becoming more proportionate, and brain development accelerates.
Here’s what else is happening:
- Hands can grasp and fingers form fingerprints
- Nostrils start to open, allowing practice breaths
- Nervous system is maturing
- Skin is still translucent but becoming less wrinkled
If your baby were born at 27 weeks, they would have a chance of survival with neonatal care - a testament to just how far they’ve come since week 13.
How to Support Your Baby’s Growth
What you do in the second trimester can support your baby’s continued development:
- Eat a balanced diet rich in iron, calcium, protein, and healthy fats
- Take your prenatal vitamins, especially vitamin D and folic acid
- Attend all antenatal appointments to track baby’s size and wellbeing
- Stay hydrated and rest when needed
- Avoid smoking, alcohol, and unsafe foods (follow NHS guidelines)
Midwife’s Top Tips
- Keep a weekly pregnancy journal to track movements, emotions, and changes
- Play music or talk to your bump - your baby can hear you from around 18 weeks
- Take bump photos to visually track growth
- Drink plenty of water to help with amniotic fluid production
- Trust your instincts - if something doesn’t feel right, reach out to your midwife
The second trimester is a time of incredible transformation. Your baby is growing stronger, more active, and more developed with each passing week. By the end of it, you’ll have a little person inside you who can hear, respond, move, and even hiccup.
Enjoy this time, connect with your bump, and celebrate every kick and milestone. Your midwife and antenatal team are always here to guide and reassure you every step of the way.
