- The life cycle begins as a single egg which divides into cells again and again.
- The baby receives nutrients from its mother.
- As time goes by it begins to change shape, and after five weeks the embryo is 12mm long.
- At about six weeks the heartbeat can be discerned.
- From the eighth week of pregnancy it is then known as a foetus and will be around 3cm long and weigh about 3 grams. Almost all of the body organs will be formed by this time.
- A rapid growth period follows when the foetus grows by about 2.5 cm per week.
- By the end of the third month, all of the vital organs are formed even down to finger/toenails!
- Later, the growth slows down, and the baby fills the uterus.
- Before birth, the baby’s reflexes are coordinated so she/he can blink, close the eyes, turn the head and respond to stimuli such as light, sounds and touch.
A newborn baby (in countries like Australia) will weigh around 2.7 to 4.6 kg and will be around 35-50 cm in length.
From birth to puberty
- During the first year of life the infant grows very rapidly. Height will be increased by 18-25 cm.
- From the first to second year of growth, children gain 10-13 cm of height.
- After this period, the growth rate slows down and becomes a steady state of around 5-6 cm per year. (Most children will have doubled their birth-height by the age of 4 years).
- This pattern continues till the child reaches puberty.
- Growth at puberty lasts about 2 years.
- The time differs for boys and girls. For girls, this happens when they are around 9-15 years old (average age = 11), whereas for boys, this happens around the age of 12-16 (average age = 12). Depending on various factors, the height gain will range from 6 to 13 cm during this period.
Mammals have many growth features in common with humans.