By just 5 weeks after conception – probably around the time you realise you've missed your period - your baby’s brain and spinal cord are already starting to develop! She's (it might be a he but we’ll stick with she in these explanations) still tiny, though – only about 7mm long.
A lot has happened in the past two weeks! By now, your baby's eyes and ears are beginning to take shape, and tiny limb buds show where her arms and legs are growing. She also has a tiny beating heart!
By the end of the 8th week, your baby has more than doubled in size, to about 1.6 cm long, and weighs about 3g (still less than a teaspoonful of sugar!). Her brain is developing very quickly, and all the muscles, nerves and organs are beginning to take shape. During this week, your baby starts to grow eyelids, and taste buds appear on her tongue!
At 12 weeks, all your baby's organs, muscles and bones are in place, and her skeleton is starting to change from cartilage into hard bone.
You might not have a bump or be able to feel your baby yet, but she's already moving and waving her arms and legs. Her heart is beating at around 180 beats per minute – that's two to three times faster than yours!
By 16 weeks your baby can sense light and sound from outside your body, as well as hear your heartbeat, and she's beginning to make facial expressions, though she can't control them yet. She's also discovering her hands – they can reach each other now, and hold on when they touch.
Halfway there! Your baby will now be about 16cm long and weigh about 300g. (In the next four weeks, though, her weight will double.) She has eyebrows, eyelashes and her own unique fingerprints now, and she's moving around more and more. You might have felt these movements by now – they usually feel like a soft fluttering or bubbling sensation inside.
Your baby has her own sleep schedule by now, which might not be the same as yours (good practice for after the birth!) Her lungs are starting to practice breathing, though of course she's still getting all the oxygen she needs from you via the placenta. Your bump will be growing rapidly now, and you'll start to really look properly pregnant!
By now your baby's really moving vigorously, and you might feel her jump in response to a loud noise – or even get a case of the hiccups! Her eyelids have opened, and she's most likely passed the 1 kg mark in weight. Her limbs are starting to fill out, and her lungs are maturing quickly. Your baby can recognise your voice now, so go ahead and talk to her – we won't laugh!
Your baby is still putting on lots of weight, and she's probably turned head-downwards by now, ready for the birth (which isn't very far away!) She can suck her thumb, and her eyes can focus, though her lungs are still putting on the finishing touches to make them ready for breathing on their own.
You've done it! At week 37, your baby is considered full term, which means that in terms of development, she's ready to meet the world! (Despite this official seal of approval, though, many babies take their time making an appearance, especially first babies – so patience is key.)
By now, her tiny finger and toenails are fully formed, and she's practising sucking and swallowing, blinking, grasping and breathing. She's pretty cramped in the uterus by now, so you won't feel quite as much movement as before, and her head may move down into your pelvis in preparation for the birth. Hang in there, your baby will be here very soon!