1. Pregnancy
Pro-life groups and conservative Christians define conception as the beginning of pregnancy. The Medical definition of the start of pregnancy is about 10 days later at implantation.

2. Conception to implantation
The zygote divides into two cells, and then they subdivide once every 12 to 20 hours as the zygote travels down the fallopian tube
5 or so days after conception the group of cells is called a blastocyst, the inner group of cells becomes the fetus and the outer cells will form the placenta

3. The outer layer of cells attach to the uterine wall by secreting enzymes
By day 9 to 12 attachment is completed and primitive placental blood circulation begins
By 14 days the very small blob of undifferentiated tissue is referred to as an embryo

5. 3 weeks
The heart begins to beat at about 18 to 21 days after conception
The embryo is 2mm long and most closely resembles a worm

6. 4 weeks The embryo resembles a tadpole and is about 6mm long
The embryo has structures like the gills of a fish in the area that will later develop into a throat
Formation of the placenta occurs

7. 5 weeks Tiny arm and leg buds form Fingerprints are detectable
The face has a distinct reptilian aspect
The embryo still has a tail and can’t be distinguished from a pig, rabbit, elephant or chick embryo

8. 6 weeks The embryo is 1.5cm long
The face has two eyes on each side of its head

9. 2 months
The embryos face resembles that of a primate but is not fully human in appearance

10. 10 weeks The embryo is now called a fetus Its face looks human
Its gender may be detectable via ultrasound

11. 3 months or the end of the first trimester
The fetus is now 5 cm long (in 6 wks it’s trebled it’s size)
Fingernails and bones can be seen
The first trimester is the main period of organogenesis
The embryo is most sensitive during the first trimester to threats such as radiation and drugs which can cause birth defects

12. The embryo during the first trimester also secretes it’s own hormones (hCG) which acts like LH to maintain the corpus luteum

13. 4 months The fetus is 20cm long
The fetus movements may begin to be felt
Its heartbeat can usually be detected

14. 5 months The fetus is 30cm long The fetus has hair on its head
Movements can be felt
At 22 weeks of gestation the fetus’ lungs may be developed to the point where it would have a 14.8% chance of survival

15. 6 months The fetus is 35cm long The lungs bronchioles develop
Interlinking of the brain’s neurons begins
Rudimentary brain waves can be detected

16. 7 months The fetus is 40cm long
Regular brain waves are detectable which are similar to those in adults

17. 9 months The fetus is 50cm long
A full term fetus is typically born at this time