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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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