A full term pregnancy can last anywhere between 37 and 42 weeks and the start of your pregnancy is dated from the first day of your last period even though conception doesn't happen until about 2 weeks later. At this time your ovary is stimulated by follicle-stimulating hormone to produce an egg which is released in to the fallopian tube. If sexual intercourse has taken place hundreds of millions of sperm are ejaculated in to the vagina, only thousands of which survive and make the journey through the cervix into the uterus and on into the fallopian tube where they will meet the ovum who has made it about one third of the way along. The sperm are chemically attracted to the ovum and attach themselves in an attempt to break through the outer coat. Only one sperm will be successful its his mission then the egg loses its attraction, hardens its outer shell and the remaining sperm let go. This whole process from ejaculation to fertilisation can take less than one hour. If you consider that an egg remains ripe for only 12 hours (max 24) and that sperm have the power to fertilise for a maximum of 36 hours, fertilisation is only likely if intercourse occurs 1-2 days before or immediately after ovulation.
|This whole process from|
ejaculation to fertilisation can take less than one hour
A single cell, known as a blastocyst, is formed when the head of the sperm fuses with the egg; this cell first divides into two within the first 24 hours and then divides continuously until by the 4th day it has become a ball of over 100 cells. The blastocyst floats free in the uterus until by the end of the first week it has implanted in to the uterine lining where food and waste pass back and forth through your blood.
The cells are now known as an embryo until week 8 when they are officially recognised as a fetus. At this stage the fetus is about the size of the full stop at the end of this sentence. The outer cells of the embryo begin to attach themselves to your blood vessels linking its self to your blood supply forming the chorionic villi, which will become the placenta. The inner cells then divide in to three separate layers, the first of which will become the nervous system and brain. The second layer will develop in to the major internal organs, the lungs and the digestive system, and the third layer will form the heart, the blood system, the muscles and the skeleton.
|The cells are now known|
as an embryo until week 8
when they are officially recognised as a fetus
The embryo now has its own blood supply some of which connect with your blood supply in the uterine wall and develop in to the umbilical cord which contains the blood vessels taking nutrients from the placenta and waste products from the baby.