Development of the fetus
Your baby is constantly growing and must go through several stages before being ready to live outside the uterus. These key moments are outlined in the following pages. The number of weeks associated with each stage (based on last menstrual period) is only an approximation and may differ from one pregnancy to the next.
First trimester: from conception to 14 weeks
At 5 weeks, the embryo’s heart begins to beat, although it cannot yet be heard during a medical exam.
At 6 weeks, the embryo measures 5 mm.
At 7 weeks, the embryo’s head is much bigger than the rest of its body. Its arms begin to form as the elbows and hands appear. The fingers are still fused together. The eyes are now quite visible.
At 10 weeks, the embryo already has a human appearance: its eyes, nose, and mouth are recognizable. Its eyelids are closed. The fingers have separated and the toes are beginning to form. Your baby begins to move their limbs, but you won’t feel any movement yet.
The embryo is now a fetus: all the body parts are in place, but are not yet fully formed. They will continue to grow and develop throughout the pregnancy.
Between 10 and 14 weeks, the fetus gets bigger and the skeletal bones begin to form.
At 14 weeks, the fetus measures around 8.5 cm. Your baby’s genitals, while not yet fully formed, are developed enough to determine their biological sex. Usually, you can find out the sex of your baby between 16 and 18 weeks when an ultrasound is performed.
Second trimester: 15 to 28 weeks
At 16 weeks, your baby’s head is still disproportionately large compared to the rest of their body, but their trunk, arms, and legs are beginning to lengthen.
Around 20 weeks, your uterus is level with your belly button. Your baby’s movements are now strong enough that you can feel them. You may feel these movements a little earlier or a little later in your pregnancy. Your baby is coated in a whitish cream known as vernix caseosa, which protects their skin.
At 22 weeks, your baby measures around 19 cm. Their hair begins to grow, and their body is covered in a fine downy fuzz known as lanugo.
Between 23 and 27 weeks, your baby puts on weight and their head becomes better proportioned to their body.
At 24 weeks, your baby can hear low frequency sounds from outside the uterus.
Around 26 weeks, your baby’s eyebrows and eyelashes are visible.
Around 28 weeks, your baby’s eyes begin to open. They will become sensitive to light at around 32 weeks.
Third trimester: from 29 weeks to birth
At 30 weeks, your baby measures around 28 cm.
At 36 weeks, your baby’s skin is pinkish, and the downy hair on their body begins to disappear, although it can remain until after the birth. Your baby is bigger because of the fat reserves they are building up.
Between 37 and 41 weeks, your baby is ready for the big day!
