What is happening to your baby:
Congratulations! One lucky sperm has beaten millions of his competitors to be united with the ovum (egg). A fertilised ovum is called a zygote. The zygote floats down the fallopian tube and divides into two identical cells. The cells continue to divide at a rapid rate. By the sixth day, a cluster of more than 100 cells has been produced. The chromosomes of mother and father form the chromosomes of the baby. Your baby's gender is determined by the sex chromosomes in the father's sperm.
By the end of the first week the cells have formed a blastocyst – a hollow, fluid-filled cluster of cells. The next two weeks are known as the germinal period.
When two ova (eggs) mature and are fertilised during a single ovulatory cycle, dizygotic (fraternal) twins are formed. The majority of twins occur in this way. Twins developing from the division of a single fertilised egg are known as monozygotic (identical) twins.
What to do:
You wouldn’t know that you are pregnant at this stage and will still be trying to conceive – enjoy! If you planned your pregnancy, you have hopefully stopped smoking, drinking and using drugs.