The New Childrens Encyclopedia

THE START OF LIFE

289

TAKE A LOOK: PREGNANCY

 DURING the first

three months of pregnancy,

called the first trimester,

the mother’s breasts

become larger. Many

pregnant women feel sick

around this time.

 DURING the second

trimester, the mother’s

breasts continue to

enlarge, her heart rate

increases, and her

enlarging womb shows as

the fetus grows inside.

 DURING the third

trimester, the mother’s

intestines and organs are

pushed up. She may feel

tired, have back pain,

and get breathless when

walking around.

Newborn babies adapt quickly

to life in the outside world. The

umbilical cord, by which it was

attached to its mother during

pregnancy, is cut. The baby takes

its first breaths, forcing its

circulation to start working.

A transparent

sac encloses the

amniotic fluid.

GROWING EMBRYO

Cells continue to divide as the embryo

develops. They become specialized, with the

head, brain, body, and heart taking shape

first, followed by the arms (initially as buds)

and, finally, the legs. From eight weeks after

fertilization, the baby is known as a fetus.

Growing embryo Three

weeks after fertilization, the

embryo is smaller than a pea

and looks a little like a tadpole.

At eight weeks, the embryo

looks more human, but is

only the size of a strawberry.

The fetus is fully developed at

24 weeks. The last stage of

development is growth.

The chorion is the

main protective sac.

Birth canal (vagina)

The umbilical

cord connects

the fetus to

the placenta.

Heart Developing ear Developing eye

Umbilical

cord

At 3 weeks the
embryo is^1 ⁄ 16 -^1 ⁄ 8 in
(2-3 mm) long.

At 4 weeks the

embryo is^3 ⁄ in

(4-5 mm) long.

 At 8 weeks the

embryo starts to move

and is 1-1^1 ⁄ in

(25-30 mm) long.

At 36 weeks the fetus

has turned head down.

It fills the uterus.

Placenta

Amniotic

fluid

THE HUMAN BODY