|
Prenatal Development
|
Timing
|
Source |
The beginnings of the various organs
and systems are established, especially in the third
week when certain key organs start to develop.
|
1st - 3rd weeks of development |
O'Rahilly, p 23 |
| The nervous, muscular, vascular, digestive,
and skeletal systems are in an incipient state. |
End of 1st month after conception |
Rugh, p 35 |
| The beginnings of many of the organ
systems, including the cardiovascular system, are
established. |
End of 4th week after fertilization |
Moore, p 91 |
| The embryo grows in length from 5
millimeters to approximately 16 to 17 millimeters. |
Day 27 to day 37 of development |
Sadler, p 220 |
| It is believed that the majority of
women do not realize they are pregnant during the
first six weeks after conception. |
6th week after conception. |
Rugh, p 54 |
| Although the embryo begins developing
immediately after conception, the most visible advances
occur during the third to eighth weeks. |
3rd - 8th weeks after fertilization |
Moore, p 2 |
| The most important features of the
body's form are determined because of the formation
of organs that occurs during this time. |
3rd - 8th weeks |
Sadler, p 108 |
| Most major organs and organ systems
are formed during the embryonic period. The mother
may not be aware of her pregnancy during this critical
period, especially in the third and fourth weeks
when the embryo is quite vulnerable. |
During 3rd - 8th weeks |
Sadler, p 106 |
| Great changes occur in appearance
because of the emergence of a disproportionately
large head and the formation of the limbs, face,
ears, nose, and eyes. |
During the 2nd month |
Sadler, p 106 |
| The embryo has a distinct human appearance. |
About day 56 after fertilization |
Moore, p 100 |
| The term embryo refers to the developing
human being during the first eight weeks after conception.
At the end of this period, all major structures
have started to form. |
End of 8th week after fertilization |
Moore, p 3 |
| The embryonic period concludes at
the end of the 8th week after fertilization and
the fetal period begins. Few, if any, new structures
are formed after this time. Development during the
fetal period involves growth and maturation of structures
that are already present. |
End of 8th week after fertilization |
Williams, p 153 |
| The beginning of all essential structures
are present. |
8th week after fertilization |
Williams, p 154 |
| The organs and systems of the body
are formed. |
From late in the 3rd week through
the 8th week |
Larsen, p 319 |
| The embryonic period consists of the
first eight weeks after the last ovulation. During
this time, the overwhelming majority ( several thousand)
of the named human structures appear, and the embryo
is about 30 millimeters in length. |
End of 8th week |
O'Rahilly, p 55 |
| Scientists have examined the embryonic
period in far greater detail than the fetal period,
which begins in the ninth week and continues until
birth. Few new features appear during the fetal
period. Instead, the structures that are already
present continue to develop. |
End of 8th week |
O'Rahilly, p 55 |
| The initial formation and development
of nearly all of the organs is complete and they
can be identified in a grossly recognizable state. |
End of 8th week of pregnancy |
Carlson, p 407 |
| The head is disproportionately large
compared with the rest of the body. |
End of 8th week of pregnancy |
Carlson, p 407 |
| The embryo has human characteristics.
The neck area is established and the eyelids are
obvious and are closing. The auricles of the external
ears begin to take their final shape. |
End of 8th week after fertilization |
Moore, p 99 |
| Squinting, incomplete closing of the
fingers, and opening the mouth can be induced by
local stimuli. |
8th week after fertilization |
Williamsn, p 169 |
|
The face is broad, the eyes are widely separated,
the ears are low-set, and the eyelids ares fused.
|
9th week after fertilization |
Moore, p 110 |
| Humans develop continuously, starting
at conception, but the changes don't stop at birth.
Obvious examples of further growth are the development
of teeth and female breasts. In addition, the brain
triples in weight between birth and age 16 years.
By age 25, most developmental changes are finished. |
|
Moore p 2 |
| Physicians can now measure how the
fetus is growing and what its state of health is
with a very high degree of accuracy. Through advanced
surgical procedures, doctors can operate on the
fetus without leaving a scar. |
|
Carlson, p 407 |
| Ultrasonic imaging is used to measure
the stages of development of the embryo. |
|
Moore, p 3 |
