4 weeks since conception
the embedded pregnancy is just visible to the naked eye
some of the chorionic villi, from which the placenta will develop, have made contact with the maternal blood supply
primitive placenta begins to produce human chorionic gonadotrophin (H.C.G.), a hormone vital to pregnancy since it prevents a menstrual period from occurring

5 weeks since conception
tissue forms down the length of the embryo which will become the nervous system; the large end will form the brain, and the rest will form the spinal cord
embryo measures 2mm

6 weeks since conception
organs begin to form; spinal cord, brain, ears and eyes have started their development
the tissue appears from which will develop the lungs, stomach, liver, pancreas, intestines and kidneys
two pairs of limb buds begin to form

7 weeks since conception
limb buds clearly identifiable as arms and legs
muscles begin to develop
earliest bone-forming centres from which the skeleton develops are present
blood vessels already extend throughout the body
intestine is almost complete but not yet in position
liver and kidneys have developed but are not yet functioning

8 weeks since conception
embryo makes first small movements, but it will be at least another eight weeks before the mother will be able to feel them
embryo is henceforth known as a fetus

10 weeks since conception
inner portion of the ear is complete and the outer ear has started to grow

12 weeks since conception
heart is completely formed and pumping blood around the fetal body and down the two arteries in the umbilical cord to the placenta, now recognizable as a separate organ
nose bridge develops
ossification continues
fetus able to move spontaneously

13 weeks since conception
fingers and toes separate into digits; nail beds start to develop
fetus weighs 30gms and measures 75mm in length

16 weeks since conception
eyebrows and eyelashes begin to emerge
all the joints in the limbs can move
external genitals have developed to the point that the gender of the fetus can be determined
hands become capable of gripping

18 weeks since conception
fetal movements can be detected by the mother

20 weeks since conception
fetus now swallows the amniotic fluid, and the kidneys produce fairly large quantities of very dilute urine
scalp hair has started to appear
soft hair known as lanugo grows over whole body


Next page

Home