|
Developmental stage |
Embryonic Stage |
Fetal Stage |
| Gestational
Age (weeks) |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
20 |
40 |
| Conceptual
Age
(weeks) |
0 |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
18 |
38 |
|
Developing Organ(s) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Central Nervous System |
|
|
|
Heart |
|
|
|
|
|
|
|
|
|
Ear |
|
|
|
|
|
|
Eyes |
|
|
|
|
Limbs |
|
|
|
|
|
|
|
|
|
|
Lip
|
|
|
|
|
|
|
|
|
|
|
|
|
Palate |
|
|
|
|
|
|
|
|
|
|
|
Teeth |
|
|
|
|
|
|
|
External
genitals |
|
|
|
|
|
|
The red bars in the table show the gestational age when different organ systems are most sensitive to major birth defects in that organ system. The
yellow bars show the gestational age when different organ systems are sensitive to functional defects and minor malformations.
Most substances that cause birth defects produce their
effect during the sensitive 5th to the 10th week (embryonic period) of
development when the major organs are forming during the first trimester . For example, thalidomide causes
limb defects when taken during the the 21st to the 36th day after conception. Tetracyclines do not produce their effects until after the first trimester
when the skeletal system begins to form bone. Some drugs such as
ethanol may produce harmful effects on functional development throughout
pregnancy
Conceptual age =The time elapsed since the day of conception
Gestational age (or “menstrual age”)= The time elapsed since the
first day of the last normal menstrual period
REFERENCES
1. Moore KL, Persaud TVN, The developing
human: clinically oriented embryology, 7th edition, Saunders, 2003:520.
2. Sandler TW. Langmans’s Medical Embryology, 7th ed.Baltimore: William and
Wilkins; 1995
3.
Engle WA; American Academy of Pediatrics Committee on Fetus and Newborn.Age
terminology during the perinatal period. Pediatrics. 2004
Nov;114(5):1362-4.PMID: 15520122
SEE ALSO: Fetal Development
Created: 11/10/2002 Mark A Curran, M.D.
All calculations must be confirmed before use. The suggested results are not a substitute for clinical
judgment. Neither Perinatology.com nor any other party involved in the
preparation or publication of this site shall be liable for any special,
consequential, or exemplary
