Making your baby

Every sperm carries a half-set of genetic information with it, including an X or Y chromosome that will determine your baby's gender. Sperm with the X, or female chromosome, swim more slowly but live longer. Sperm with the Y, or male chromosome, swim more quickly.

Sperm swim at the rate of seven inches per half-hour, occasionally stopping to rest, because swimming is hard work- they have to beat their tails 800 times just to move 1/3 of an inch. Sperm and eggs can only survive 24 to 48 hours after they leave the comfort of the scrotum or ovary. But if all conditions are right, the sperm and egg will join in the fallopian tube.

When the strongest and fastest sperm reach the egg, they become hyperactivated, ramming their enzyme-coated heads at it to break down and dissolve the egg's outer shell. Eventually, one lucky sperm will break through and the egg instantly shuts down, so no more sperm will be admitted.

The chromosomes of the egg and sperm then fuse together, assigning your future baby a gender, hair colour, eye colour and hundreds of other genetic characteristics. Identical twins or multiples may be formed if the egg then splits in two. Fraternal twins or multiples will be formed if more than one egg gets fertilised.

Your progress

Conceiving

For conception to occur, conditions must be just right inside your body. Your cervical fluid must be exactly the right consistency. If you have a 28-day cycle, this happens about 14 days after your period starts. As your 24- to 48- hour window of fertility approaches, your cervical fluid will change texture from watery to creamy, then become slippery.

Once an egg has fertilised, fibrae sweep the tiny ball of cells, now transformed into a blastocyst, down the fallopian tube and into the top of the uterus. Once there, the fertilized egg burrows into the lining of the uterus. If the fertilized egg implants, the site of implantation will be the place where the placenta attaches to the uterine wall.

After the blastocyst has implanted, it emits hormonal signals that tell the lining of the uterus to stay in place, instead of disintegrating and shedding as it normally would during menstruation.

What to think about

Even before you miss a period, you may have an intuitive sense that something's different. You may feel bloated as if with PMS, have a strange taste in your mouth, or your breasts may feel a little odd - the first faint clues that a baby is burrowing in to take you on the adventure of a lifetime.