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Developmental Stage Calculator

Find out how far along you were in pregnancy on a particular date with our calculator. The
calculator  assumes 28 day cycles with ovulation on day 14 of the cycle.

First day of last Menstrual period

How far long was I on  ?

The chart below shows the age when different organ systems are developing.
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    
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 pink 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

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

Created: 11/10/2002 Mark A Curran, M.D.



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