Prenatal Development Timeline! By MonicaV Period: Jan 1, 2017 to Jan 14, 2017 Period Of Zygote First 2 Weeks Period: Jan 1, 2017 to Feb 19, 2017 First trimester week 1 through week 12 Period: Jan 1, 2017 to Sep 30, 2017 Full term pregnancy 40 weeks and 6 days Period: Jan 15, 2017 to Feb 19, 2017 Period Of Embroyo Week(s) 3 -8 Period: Feb 26, 2017 to Mar 4, 2017 Period Of Fetus 9 Week Birth Period: Mar 26, 2017 to Jun 11, 2017 Second trimester Week 13 to week 27 Period: Apr 29, 2017 to May 20, 2017 Week of sex detection 18 - 20 weeks Period: May 14, 2017 to May 14, 2017 Week of viable birth Period: Jul 28, 2017 to Sep 30, 2017 third trimester Week 28 until your due date