Around the end of week two, or 14 days before the anticipated start of your next period, one of your ovaries will release an egg (ovum) which begins to travel down your fallopian tubes. Your egg will live for about 24-48 hours after being released from the ovary. We call this part the 'amazing race' as it must be fertilised in this short amount of time if you are going to conceive.
At this stage of ovulation your body increases its production of hormones to prepare your uterus to receive and nourish a fertilised egg. Increased oestrogen levels cause your uterus to form a blood rich lining of tissue called the endometrium. Increased progesterone levels help to prepare your uterus to support a fertilised egg. The mucus in your cervix will also thin out, forming a welcoming environment for sperm and promoting fertilization.
Fertilisation occurs in the outer part of the fallopian tube. During intercourse your partner will release between 200-500 million sperm; fertilisation will occur if just one of these sperm fuses with the egg your body has released. As soon as this fertilisation occurs, the outer layer of your egg (now called a zygote) will harden and all other sperm will drop off. Your egg then starts its cell division process whilst continuing down the fallopian tube towards the uterus.
The sex of your baby is determined the moment your egg is fertilised.
The human body is made up of 46 chromosomes that carry our genetic information. The sperm and egg each have 23 chromosomes which fuse to form the 46-chromosome blastocyst, the name for this first group of cells which will become your baby. Your baby's gender is determined by just two of these chromosomes, one from your egg and one from your partner's sperm. Female eggs always carry the X (female) chromosome, but sperm can have either an X (female) or Y (male) chromosome, hence determining whether your baby will be a boy or a girl. If your egg is fertilised by a sperm carrying the X chromosome, your baby will be a girl (XX). If your egg is fertilised by a sperm carrying the Y chromosome, your baby will be a boy (XY).
Once your egg is fertilised, your baby continues to form rapidly, his or her cells continuing to divide as they continue their journey to the uterus.
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