Pregnancy and Conception Date

Most doctors from family planning services will calculate the start of pregnancy from the first day of your last menstrual period. The menstrual age is about two weeks ahead of when conception actually occurs. The day of conception is sometimes the day you’ve had sex or sometimes it can be a few days later. Sperm can live in the body for up to seven days.

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The Start of Conception


Every month in one of the woman’s two ovaries a group of immature eggs will start to develop in small fluid filled cysts. These are called follicles. During this process the body will select one of these follicles to complete the maturation process.

The chosen follicle will halt the development of any of the other follicle. The other follicles will stop growing and degenerate. This follicle will then rupture and release the egg from the ovary. Ovulation will then typically occur about two weeks before the next menstrual cycle begins.

Release of Egg

When the egg is release it will then travel into the fallopian tubes where it remains until a single sperm penetrates it during the fertilisation. The egg can be fertilised for around about 24 hours after ovulation.

Development of Corpus Luteum

After the ovulation occurs the ruptured follicle will then develop into a structure that’s known as the corpus luteum. This secretes two hormones which are progesterone and oestrogen. The progesterone helps to develop the endometrium meaning the embryo can implant by thickening the endometrium lining.

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When the sperm does meet and penetrate the egg during ovulation, fertilisation will happen. After the sperm penetrates the egg, changes will occur to the protein coating around it which prevent any other sperm from entering.

As soon as fertilisation begins your baby’s genetic make-up is then complete. This includes everything from determined sex to hair colour and much more. The mother provides the X chromosome as she is an XX and if a Y sperm fertilises the egg then the baby will be a boy with the chromosome XY. Whereas if an X fertilises the egg then the baby will be a girl and have the chromosome XX.


Within the 24 hour period after fertilisation the egg will already begin developing rapidly into many different cells. The egg will remain in the fallopian tubes for up to 3 days. The fertilised egg will continue to divide as it passes through the fallopian tube to the uterus where its next job is to attach to the endometrium.

The fertilised egg is then known as zygote from this point. The zygote becomes a solid ball of cells, which then changes into a hollow ball of cells called a blastocyst. Before implantation the blastocyst breaks out of its protective coating.

The blastocyst establishes will then make contact with the endometrium, an exchange of hormones then helps the blastocyst to attach. Some women might have spot bleeding occur for a day or two after implantation. After this happens the endometrium will then become thicker and the cervix will be sealed by a plug of mucus.

During the first three weeks the blastocyst cells begin to grow into a larger clump of cells within a that small ball. By this point the baby’s first nerve cells have already formed. From the moment of conception to the eight week of your pregnancy many medical professionals will refer to the baby as an embryo. After this point your developing baby will typically be referred to as a foetus.

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During the conception process if no sperm is around to fertilise the egg then the corpus luteum will degenerate removing the high levels of hormones. The endometrium will then slough off which results in the natural cycle occurring again and the woman will receive their normal menstrual bleeding.