Gastrulation occurs after 3 weeks of fertilization, forming the three germ layers - ectoderm, endoderm, and mesoderm. During the first week, membranes form to protect and nourish the embryo, including the amnion, yolk sac, chorion, and allantois. From weeks 12-23, the fetus grows to 25 cm and 0.5 kg, developing features like eyebrows and eyelashes. The heartbeat can be heard and the mother can feel movement. Later, the fetus assumes a fetal position and the sex is apparent as bones and other organs develop.

2.  Transition : after 3 weeks of fertilization a
process called gastrulation takes place this
comes from 3 cells

3.  Ectoderm- is the outer layer it forms the
embryo’s skins and central nervous system.
Endoderm-is the inner layer it forms the lungs
and digestive track
Mesoderm- is the middle layer forms most of the
other organs.

4. During the first week membranes form and
protects the embryo as well nourishes it.
 the amino membrane forms the fluid like sac.
 The yolk sac membrane contains no yolk and
produces first blood and eventually turns into
gametes
 Chorion turns into the embryos potion of the
placenta
 Allantois forms the part of the umbilical cord
that connects the embryo to the placenta.

5. During week 12-23
The fetus length expands to 25 cm. and weight 0.5
kg. they start developing eyebrows and eyelashes
with a face of an infant .
 At this point the heart beat can be heard and
fetus can be active. The mother can feel flutters
pokes and kicks.

6.  Form into a fetal position
 Sex of fetus is apparent
 Baby skeletons develops bones
 Baby begins to hear
 Fingerprints and footprints form

7. Week 24-40
 Baby's eyes open
 Baby bones are fully developed
 baby's central nervous system has matured to
the stage where it can control body
temperature
 Baby's fingernails grow
 Rapid gain weight begins
 Week 40 your due date arrives