This calculator estimates the age of a fetus on a particular date based on the last menstrual period (LMP). The calculator assumes a standard cycle length of 28 days with ovulation around day 14, but you may adjust the cycle length if known.
The chart below shows the age when different organ systems are developing. The calculator assumes 28-day cycles with ovulation on day 14 of the cycle unless you adjust the cycle length above.
| 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 .
Conceptual age = time elapsed since the estimated day of conception.
Gestational age (or “menstrual age”) = 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 ed., Saunders, 2003:520.
2. Sandler TW. Langman’s Medical Embryology, 7th ed. Baltimore: Williams and Wilkins; 1995.
3. Engle WA; American Academy of Pediatrics Committee on Fetus and Newborn. Age terminology during the perinatal period.
Pediatrics. 2004;114(5):1362–1364. PMID:
15520122.
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.
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