Trimester |
Week |
Development |
| First Trimester |
1 |
First day of menstrual period |
| |
2 |
Uterus preparing tissue lining. Eggs ready for release in fallopian tube |
| |
3 |
| Fertilization occurs. Baby's sex determined by male chromosomes |
|
| |
4 |
|
| |
5 |
| Digestive tract, heart, nervous system and brain all start to form |
|
| |
6 |
| Embryo Is 1/4 inch in length. Arm and leg buds start to form |
|
| |
7 |
| Lungs, kidneys and eyes are developing |
|
| |
8 |
| Measures around 2.5cm, Webbed fingers and toes develop |
|
| |
9 |
| Finger partially separated. Liver is forming and producing blood cells |
|
| |
10 |
| 6cm in length. Leg bones and facial features are recognisable |
|
| |
11 |
| 7cm in length. All major internal organs fully formed |
|
| |
12 |
| 8cm in length. May be able to see moving limbs in scans |
|
| Second Trimester |
13 |
| Vocal chords form, liver secrets bile and pancreas produces insulin |
|
| |
14 |
| 9cm long. Fully functional hands. Practicing inhaling and exhaling |
|
| |
15 |
| Fine skin and Lanugo, fine hair covers body. Can pick up heart beat. |
|
| |
16 |
| Limbs move frequently. Bones harden and finger and toe nails form |
|
| |
17 |
| Baby can suck, swallow and blink, Fat is developing under the skin |
|
| |
18 |
| Weighs over half a kilo, prostate develops in male |
|
| |
19 |
| Placenta is as big as baby and is source of all nourishment |
|
| |
20 |
| Scalp hair grows and uterus develops in female |
|
| |
21 |
| Growth and development begin to slow off. Heart becomes stronger |
|
| |
22 |
| Eyelids and eyebrows form. If males testes descend |
|
| |
23 |
| If born prematurely now this baby still has a chance of survival |
|
| |
24 |
| Further development of muscles, bone and tissue |
|
| |
25 |
| Nostrils open and spine structures are in place |
|
| Third Trimester |
26 |
| Air sacs develop in lungs, covered in surfactant to aid breathing |
|
| |
27 |
| Baby is 40cm long. Brain develops, retinas develop, |
|
| |
28 |
| Baby is plumper and rounder, body mass is 4% fat. |
|
| |
29 |
| Capable of basic breathing and temperature control. Senses working |
|
| |
30 |
| Lanugo disappearing. Bone marrow is producing the red blood cells now |
|
| |
31 |
| Brain and lungs undergo rapid development. If male, testes descent to scrotum |
|
| |
32 |
| Baby weighs two kilograms. Head hair is growing. All senses working |
|
| |
33 |
| Body fat turns skin from red to pink. Brain growth means head is large. |
|
| |
34 |
| Baby responds as a new born. Immune system develops |
|
| |
35 |
| Baby occupies most of uterus and there is little room for movement |
|
| |
36 |
| Baby is almost ready. Limbs have plumped up |
|
| |
37 |
| Weighs around 3 kilos. Can grasp and turns towards the light |
|
| |
38 |
| Head and abdomen of similar size. Has accumulated meconium (bowel movement) |
|
| |
39 |
| Weighs around 3.5 kilos, Surfactant increased in lungs. Very crowded |
|
| |
40 |
| Baby is soon ready to be born. Approximately 60cm long |
|
