It's very important to be aware of the risk of ectopic pregnancy - a pregnancy which develops outside the womb - if there is any chance you might be pregnant. 'Also, some women have what's known as a low HCG pregnancy where the hormone levels aren't as high as usual these women may continue to experience periods throughout their pregnancy - although this is very rare.' 'But it's usually a much smaller amount and can be pinkish in colour rather than red.

However, for some women who have an irregular cycle, it may come later,' explains Halliday. 'Implantation bleeding usually occurs earlier than a missed period would, as it's when the embryo implants. This could be due to implantation of the embryo, or a sign of low hormone levels. Surprisingly, too, some women may be pregnant despite having what they believe to be a period.