You’re pregnant – hooray! There’s a little dumpling, or dumplette, growing inside your uterus.

But, err… now what?

Welcome to the first of three stages of pregnancy.

In those first 12 weeks, your baby grows faster than at any other time in your pregnancy, changing from the size of a poppy seed to a lime.

LISTEN: Bec Judd and Monique Bowley talk all things stages of pregnancy on Mamamia’s new pregnancy podcast, HELLO, BUMP. Post continues… 

It’s a time that begins from the first day of your last period and lasts until the end of week twelve.

And since most people don’t discover they are pregnant until week five or six (the week they notice that, you know, their period is M.I.A.), the first trimester is halfway over before you’ve even noticed it began.

So, to make the most of the here’s everything you need to know about what goes down during your baby’s first three months of growth.

The physical changes in your body.

There’s A LOT of hormones going around your body right now. And while the most obvious sign of pregnancy is a missing period, there are lots of other physical signs your body is busy growing a tiny human.

Things like extreme tiredness, tender and swollen breasts, an upset stomach (a.k.a. 'morning sickness'), mood swings and constipation are all normal in the first trimester.

Making changes to accommodate your growing baby.

While it's best to talk to your doctor about what you can and can't do while pregnant, the general consensus is that drinking alcohol, doing drugs and smoking are strictly off-limits, not just in the first 12 weeks, but throughout all stages of pregnancy.

Raw or undercooked meat, unpasteurised dairy, raw eggs and liver are not recommended for eating while pregnant, and if you're a coffee lover it may be time to switch to decaf... so chat to your doctor about the lifestyle changes you should be making during this time.

How your baby is growing.

At week four, your baby is a teeny tiny poppy seed. By week five, they are the size of a little fingernail, and their face is beginning to form.

'Tadpole week' is week six, but by week eight they are resembling a little tiny person.

By week nine baby has an eye colour and eyelids, and their genitals are starting to develop.

At week eleven, your baby has developed miniature fingernails. And by week twelve, everything is in place - the organs, bones, limbs, muscles and sex organs have all developed.

And if you're tired at the end of your first trimester from all of this work, we don't blame you, you've done a great job at incubating, lady.

By the end of your first trimester, your little human is fully formed, but they are still only the size of a lime or a plum.

All that's left for baby to do is grow as your enter the next trimester of your pregnancy.