When it came to Duchess Catherine's pregnancy, we watched her bump grow and made (pretty accurate) guesses at when her sweet baby prince would be born. How? Well, because she knew she was pregnant therefore we knew so too… But what about those stories you hear about women who just, one day, wake up and are seven months pregnant?

Such is the case of 22-year-old Tia Freeman, who, just last week, thought she was suffering from stomach cramps brought on by food poisoning, but was actually IN LABOUR.

Tia's shock pregnancy left her delivering her own baby in a hotel room in Germany.

Wait, what? How? Who? When? Yes, we've been left asking ourselves the same questions: how do you NOT know you're pregnant? Here, Dr Philippa Costley, a spokesperson for the Royal Australian and New Zealand College of Obstetricians and Gynaecologists explains how this can happen – and the hidden dangers associated with it…

What are the reasons behind someone not knowing they’re pregnant until so far into their pregnancy, or even just discovering they’re pregnant as they’re giving birth? How is this possible?

There are many reasons a woman may not know she is pregnant. She may have irregular periods and so a delayed or missed period may not be alarming. Another reason may be she is taking regular contraceptives and may not be aware when this has failed.

Some women do not gain a lot of weight during pregnancy from either carrying a small baby, or improving their general condition (i.e. losing fat) during the pregnancy and thereby not increasing their overall weight.

Many mothers say that the movements of the baby would be difficult to miss, however, some women do not feel movements as much as others. This could be because the baby is less active, the placenta is in front of the baby, or the mother has a lowered perception. Saying this, it is rare for a woman to enter the second or third trimester without realising she is pregnant.

Despite finding out about her pregnancy so late in the game, Tia, and Xavier, are both happy and doing well.

Are there any negative consequences of not knowing your pregnant – to the mum and/or the baby?

Absolutely! Women who do not know they are pregnant will not present for antenatal care. They may not avoid smoking, alcohol or illicit drug use. They also may not be taking folate supplements, which is recommended for all women during pregnancy.

They may engage in activities that could be dangerous to the pregnancy such as deep sea-diving or bungee-jumping. They may be taking medication that is not safe in pregnancy.

Without antenatal care, complications of the pregnancy such as pre-eclampsia or gestational diabetes, may not be identified so both the mother and baby could be at risk.

Lastly, women who don't know they are pregnant sometimes have issues bonding with their baby as they have not had this special time during pregnancy. It increases their risk of perinatal depression and anxiety.

Can you be pregnant and not know it and still have your period?

It is not possible to continue to have regular periods whilst pregnant. However, some women have bleeding during pregnancy which seems to be at the same time as their period would be due. It is extremely rare for this to continue beyond the first trimester.

Any bleeding in pregnancy needs to be assessed by your doctor as it can be an indication that there is a complication of the pregnancy.

Want more information about pregnancy signs and symptoms? Book an appointment with your trusted GP or a gynaecologist today.