Fetal development - From Fertilization to week 6
1 Week (3 weeks since last menstrual period)
Fertilization takes place. Genetic identity is complete including hair and eye color, gender, etc.
2 Weeks (4 weeks since last menstrual period)
Implantation occurs.
3 Weeks (5 weeks since last menstrual period)
The heartbeat is detectable as early as 18 - 22 days by ultrasound. The following start to form: heart, brain and spinal cord, muscles, skeleton, and pancreas.
4 Weeks (6 weeks since last menstrual period)
Blood circulation begins. Mouth opens. The following start to form: brain chambers, eyes, ears, arm buds, thyroid, vertebrae, spine, ribs, kidney, liver, and umbilical cord.
5 Weeks (7 weeks since last menstrual period)
Embryo is the size of a BB pellet. Brain divides, pancreas begins producing insulin, body begins blood circulation, nerves extend into limb buds. The following start to form: leg buds, heart chambers, nostrils, appendix, intestines, eye lenses, and inner ear.
6 Weeks (8 weeks since last menstrual period)
Embryo is the size of a pinto bean. The spine is clearly visible. The heart beats 150 times per minute. Brain waves are measurable. The following form: eyelids, nose, heart valves, fingers, blood cells, and joints. The embryo hiccups and has slow body movements.
Fetal Development - 7 to 12 Weeks
7 Weeks (9 weeks from last menstrual period)
Embryo is the size of a lima bean. The fingers, toes, elbows and knees are distinct. Internal organs are visible. Genitals are visible, skull bones are growing together and the immune system starts forming. Moves body, limbs, hands.
8 Weeks (10 weeks from last menstrual period)
The size of a small plum. All organs are present. The central nervous system begins and the primitive skeletal system is complete. Joints complete and teeth buds form. The end of the embryonic period.
9 Weeks (11 weeks from last menstrual period)
The unborn child is from this point until birth, called a fetus. Fetus is 2.4 inches from crown to rump. Brain activity in response to pain or noxious stimuli. Head position shifts. Kidneys produce urine and chest wall expands in early respiratory movements. Pupils form.
10 Weeks (12 weeks from last menstrual period)
Bones harden, body hair forms, external genitalia visible. Digestive tract contractions and fetus produces hormones. Opens mouth, squints and moves fingers and toes. Extends arms and hands.
11 Weeks (13 weeks from last menstrual period)
Fetus is 3 in. long and the size of a peach. Swallows and responds to touch. The body now grows faster than the head.
12 Weeks (14 weeks from last menstrual period)
4 inches long. Gender can be distinguished. Body and organs are complete. Fetus grasps objects. Moves in jerks, flexes arms, and kicks.
Fetal Development - 13 to 24 weeks
13 and 14 Weeks
Blood vessels visible. Slow eye movements visible via ultrasound. Brings hands together, sucks thumb, and moves arms and legs.
15 and 16 Weeks
Fetus is 4.8 to 5.6 inches and about the size of an adult hand. Body fat begins to form under the skin. External ears stand out from head. Fetus actively turns inside the womb.
17 and 18 Weeks
Fetus is 6 to 6.4 inches from crown to rump. Mouth and lips are formed. Eyes are closed but will move hands to block light. All important physiological systems have developed.
19 and 20 Weeks
Fetus is 7.2 to 7.6 inches from crown to rump. Eyelids and eyebrows are complete. Fingernails are complete and reproductive organs are formed in girls.
21 and 22 Weeks
Fetus is 8 to 8.4 inches from crown to rump and weighs 1 to 1.2 lbs. Body fat increases. Fetus can be startled by sound.
23 and 24 Weeks
Fetus is 8.8 to 9.2 inches and can weigh up to 2 lbs. Can possibly survive born at 23 weeks and has a 50% chance of survival if born at 24 weeks.