Stages of Pregnancy

Fetal development during pregnancy
(prenatal development milestones)

What happens from conception to birth
– pregnancy week by week

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Embryonic Period
Week of Gestation
1	A single sperm penetrates the mother’s egg, this cell is called a zygote.As it travels down the Fallopian tube the zygote divides to form a ball of cells.When it has formed a group of inner cells with an outer shell it is called a “blastocyst”.The inner cells eventually become the embryo while the outer group of cells become the membranes that nourish and protect it. By the 6th day the blastocyst implants into the uterine wall and sticks here tightly, by this time the lining of the uterus has grown and is ready to provide nourishment via the mother’s blood stream. It puts down tiny roots which eventually become the placenta.
2	The cells of the embryo divide rapidly and begin to take on specific functions, this process called differentiation produces the varied cell types that make up a human being.Three layers of cells develop; the ectoderm, the endoderm and the mesoderm.
3	By the 21st day, the neural plate begins to form into the neural tube, which will eventually develop into the spinal cord. Tiny blood vessels begin to form and the heart starts to develop.
4 to 5	The amniotic sac is formed. The neural tube should close by the end of week 4, if it does not close properly spinal cord defects occur. By the 5th week the main parts of the brain; the forebrain, midbrain and hindbrain, develop further. Arm and leg buds are visible.
6	Feet and hands can be seen to develop. The tiny heart will start to beat rapidly. Beginning of formation of the lungs. ‘Reflex’ motion starts.By the end of the sixth week the basic development of the five brain vesicles is complete.
7	All essential organs have begun to form. The first parts of the body experience sensitivity.
8	By the end of the 8th week of gestation (10th week of pregnancy) the basic components and organs of your baby are formed, the blueprint for your baby is complete. Facial features including external features of ears develop. Between 8 to 10 weeks all of the basic parts of the brain are in place.

Fetal Period
Week of Gestation
9 to 12	The fetus reaches a length of about 3.2 inches. Eyes are formed but not ‘connected’ by the visual cortex. The first synapses start to form in the brain. The head is now half the size of the fetus. The fetus can make a fist with its fingers. ‘Deliberate’ motion starts.
13 to 16	The fetus reaches a length of about 6 inches.Lanugo (fine hair) develops on the head. Some bodily functions will start now, such as swallowing and urination. Taste buds are forming, baby can ‘taste’ amniotic fluid. The brain is multiplying at a rate of 250,000 cells per minute.
20	The fetus reaches a length of about 8 inches. The ears are fully formed; ‘hearing’ is possible. Lanugo covers the entire body. The fetus responds to touch around week 22. A waxy substance ‘vernix’ is covering its skin to stop it getting waterlogged by amniotic fluid. The mother can usually feel the fetus move.
24	The fetus reaches a length of 11.2 inches. Eye components are well developed. The myelination process begins; this means that the axons (the ‘wires’ that connect the brain cells) gain their fatty protective covering.
25 to 28	The fetus reaches a length of 15 inches.From week 25 the brain undertakes another phase of rapid growth. Eyes will open and start blinking around week 26. Nervous system is developed sufficiently to control some body functions. A baby born at this time has a 90% chance of survival.
29 to 32	The fetus reaches a length of up to 17 inches. (between 15 – 17). From week 28 the fetus is swallowing up to a litre a day of amniotic fluid. Around week 29 apoptosis begins; the brain's natural ‘pruning’ process. Rapid breathing movements occur. By week 32 nearly every part of the body is sensitive to heat, cold, pressure and pain. The fetus begins storing iron, calcium and phosphorus.
36	The fetus reaches a length of up to 19 inches. (between 16 – 19). Lanugo begins to disappear. A baby born at 36 weeks has a high chance of survival.
37 to 40	The fetus is considered full term at 37 weeks. Lanugo is now gone except for upper arms and shoulders.Ready to greet the world!

Pregnancy can be split into two distinct phases:

The embryonic period in which the cells and organs are formed
The fetal period in which the networks are built allowing them all to communicate. The fetal period is a period of growth where the organs grow and develop; body and brain systems connect and establish themselves to complete the growth cycle towards birth.

By the end of the 8th week of gestation (the end of the embryonic period) the basic components and organs of your baby are formed. It is a critical period where it is thought that most congenital deformities occur. It is before this period, prior to conception that you should quit smoking, alcohol and drugs and concentrate on maintaining a balanced diet for good nutrition; Click here for more information on diet and nutrition during pregnancy specifically watch your intake of essential fatty acids. Click here for more information on efa's

For more information on brain development - Click here
For a plan of activities that can be undertaken during this period before birth - Click here

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Stages of Pregnancy

Fetal development during pregnancy (prenatal development milestones)

Fetal development during pregnancy
(prenatal development milestones)