3 min read · Around weeks 13–16 of pregnancy
Welcome to the second trimester.
Your baby is still small enough to fit comfortably in your hand, but growth is speeding up and movements are becoming increasingly coordinated.
During approximately weeks 13 to 16, the head becomes more proportionate to the body, bones strengthen, facial features continue changing and the nervous system supports more movement of the arms and legs.
How big is your baby at four months?
At around week 13, an average fetus measures approximately 7.4 cm from head to bottom — around the size of a peach.
By week 16, this has increased to around 11.6 cm, often compared with an avocado.
The numbers are fascinating, but they are only averages. Growth varies naturally between pregnancies.
Your baby's body is becoming more proportionate
Earlier in pregnancy, the head makes up a very large part of your baby's body.
During the second trimester, the body begins catching up. The head becomes rounder and more proportionate, while the neck becomes more defined.
The arms and legs are lengthening too.
Owloo Insight
Your baby is moving more than you probably realise.
The arms and legs are active during this stage, even if you cannot feel those movements yet.
Bones and muscles keep developing
The skeleton continues hardening, particularly the longer bones of the arms and legs.
Muscles and the nervous system are developing alongside them, allowing your baby's movements to become more organised.
By around week 16, the hands can form fists and the face can make tiny movements. These are not intentional expressions yet — they are part of developing muscle and nerve function.
Can you feel your baby yet?
Possibly — but it is also completely normal if you cannot.
First movements are noticed at different times. For many parents, they become recognisable later in the second trimester.
The first sensation may not feel like a kick at all. Parents often describe something much subtler at first: a flutter, bubble or gentle movement.
Owloo Moment
The bump may finally be becoming part of your photographs.
Take a simple side-profile photo this month. Repeat it later in pregnancy and you may be surprised by how much changes in only a few weeks.
What happens next?
Over the next month, growth continues rapidly and some parents begin noticing the first movements more clearly.
You are also moving closer to the mid-pregnancy ultrasound, when healthcare professionals can examine your baby's anatomy in more detail.
Hello World Kit | 0–6 months
As your baby grows inside the womb, you can slowly begin imagining life after the first hello. The Owloo Hello World Kit brings together thoughtful play companions for your baby's earliest six months.
Discover the Hello World Kit
Frequently asked questions
How big is a baby at 16 weeks?
An average fetus is approximately 11.6 cm from head to bottom at 16 weeks, although individual growth varies.
Can my baby move at four months pregnant?
Yes. Movement is already happening, but you may not yet be able to feel it.
Can you feel kicks at 16 weeks?
Some parents may notice early movement around this period, while many will notice it later. There is a wide normal range.
What is developing at four months pregnant?
Bones continue hardening, the nervous system develops further, the body becomes more proportionate and movement of the arms and legs increases.
The Owloo approach
This month often sits beautifully between two worlds: pregnancy is becoming more visible, while your baby's movements are still mostly a private secret inside you.
Growing quietly. Moving gently. Getting closer every day.
Written by Tina Krapez, Owloo Co-founder & COO
Tina Krapez is the Co-founder and COO of Owloo, where she helps create thoughtful products and educational resources supporting families from pregnancy through early childhood.
Sources and further reading
