If you want three kids, there's a specific age a woman should start trying to conceive for the best possible chance.

Fertility is a major issue for many couples and the common wisdom, whether right or wrong, is that the younger you are, the better your chances of conceiving. Professor Mary Wingfield of Merrion Fertility has backed up the theory. Speaking on RTÉ Radio 1 last year, she said that for women, "if you are 35, you have half the chance of getting pregnant as somebody who is 25." She also said that anyone looking for a big family will have to start relatively early.

"If you want to have a 90 per cent chance of having three children, you need to start trying to get pregnant when you are 27."

Prospective dads have a slightly bigger window of fertility, but Mary confirmed that age is also a factor for them.

"Once men go over the age of 40, it reduces their fertility by about 50 per cent."

She said that while the statistics are stark, age is the main factor in fertility.

"Knowing your age is the most important thing. If you are 30, you need to start thinking about it very soon."

Plenty of women do of course manage to conceive at all stages of life and we know that your health is also a huge factor - something to keep in mind if the number 27 is giving you a sudden panic attack.