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. Author manuscript; available in PMC: 2012 Oct 1.
Published in final edited form as: Birth Defects Res B Dev Reprod Toxicol. 2011 Oct;92(5):404–412. doi: 10.1002/bdrb.20326

Table 1.

Gestational Milestonesa for Mammals

Species Implantation Primitive streak Early differentiation Organogenesis ends Usual parturition
Rat 5–6 8.5 10 15 21–22
Mouse 5 6.5 9 15 19–20
Rabbit 7.5 7.25 9 18 30–32
Hamster 4.5–5 7 8 13 16
Guinea Pig 6 12 14.5 ~29 67–68
Monkey 9 17 21 ~44–45 166
Human 6–7 13 21 ~50–56 266
a

In gestational days; day of confirmed mating = gestational day 0. (Reproduced with permission from DeSesso, J. M., (2006) “Comparative Features of Vertebrate Embryology,” Chapter 6 in Developmental and Reproductive Toxicology: A Practical Approach, 2nd Ed., R. D. Hood, Ed., CRC Press, Inc., Boca Raton, FL, p 147–197.)