Prenatal Development By jc010851 Period: Jan 1, 2017 to Jan 15, 2017 Period of the Zygote Period: Jan 15, 2017 to Feb 26, 2017 Period of the Embryo Feb 7, 2017 Start of First Trimester Period: Feb 26, 2017 to Sep 24, 2017 Period of the Fetus Mar 2, 2017 Start of Second Trimester May 7, 2017 Week of sex detection Jun 4, 2017 Start of the Trimester Jul 9, 2017 Week of viable birth Sep 24, 2017 Full Term Pregnancy