First Trimester

Month 1 weeks 1-4
Conception occurs on week 2-3 at the fertilisation of an egg. Within the first couple of weeks after conception, the amniotic sac and placenta form, the face, eyes and ears begin to develop, and lungs and heart start to form.


Month 2 weeks 5-8
The face continues its development, limbs begin to form, and the brain, sensory organs, and the digestive tract begin to take shape. Cartilage begins to be replaced by bone. After about 5 weeks, the heartbeat can be detected with an ultrasound.


Month 3 weeks 9-13
Limbs, as well as the hands, feet, fingers, and toes, become well developed, and fingernails and toenails begin to form. The external ears and teeth begin their development, as well as reproductive organs. By the end of this month, the body and organs are all formed, though needing time and nutrition to mature, and from head to toe the length is 7-8cm.

Second Trimester

Month 4 weeks 14-17
Unique finger prints develop. Baby begins to stretch, yawn, suck their thumb, and make faces. The reproductive organs are now visible on an ultrasound. By the end of the 4th month, the body is about 15cm long.


Month 5 weeks 18-21
This month movements can be felt. Hair growth continues on the head and body, including eyebrows and eyelashes. Eyelids and nails become well developed. At the end of month 5, the baby is over 20cm long.


Month 6 weeks 22-26
The skin is still translucent yet reddish and wrinkled. Finger and toe prints become well developed. The eyelids become parted, and the eyes can be opened. Your baby will respond to external stimuli, such as sounds, by increasing their pulse or moving. You may experience your baby’s hiccups in jerk-like motions. At the end of month 6, your baby is about 35cm long.

Third Trimester

Month 7 weeks 27-30
Existing organs and body systems continue to grow and develop and an addition layer of fat will begin to be stored. At this stage, hearing is fully developed, and eyelids open, and the baby will react to sound, pain, and light and will often change position. At the end of this month, baby will be as long as 40cm and weigh up to 1.5kg.


Month 8 weeks 31-34
Fat stores are increased and rapid development of the brain occurs. The baby can see at this stage and will begin to kick more. Most of the internal organs and systems are fully developed, but the lungs still need time to mature.


Month 9 weeks 35-40+
The lungs become mature in preparation for birth, and reflexes become more coordinated, allowing the baby to respond to sounds, blink, grasp, and turn their head. The baby may move less during the last few weeks as they move into position for birth. Baby is now up to 50cm and weighs around 3kgs.


For more developmental information see https://www.babycenter.com.au/pregnancy-week-by-week