Schematics

By the end of the first month
after conception, a simple
functioning circulatory system
has developed in the embryo.
The spinal cord is closed and
the embryo is 1/6 inch long
(4mm).

At the end of the second month
the cardiac valves and four
chambers of the heart are
established and functioning.
Nervous system development
has begun, and so has motor
activity.

In the third month, the fetus
jerks its body and flexes its
tiny legs and arms. Weight is
3/4 ounce (21 grams), about
the same as a letter.

During the fourth month the
fetus reaches almost 6 inches
(15cm) in length. Arms and
hands are fully shaped with
fingernails. Feet and legs
are fully molded, and hair
has already started to appear.

In the fourth and fifth month
the fetus begins reacting to
sound, and hair becomes
courser and colored.

In the sixth month the fetus
is over 12 inches (30 cm)
long. The thumb is actively
involved in grasping. The
inner ear is structurally
capable of functioning.

In the seventh month taste has
probably been established.
From now until term, fetal
length increases from
approximately 13 to 20 inches
and weight nearly triples.

By the eighth month lungs are
maturing and the fetus
continues to practice the
motions of breathing.

On the average, delivery
occurs at 40 weeks, although
there is a normal variation of
two weeks on either side
(38-42 weeks).