By the end of this week your baby will be about half a centimetre long and shaped like a tadpole with a protrusion like a tail at the end of the spine.
If you had an ultrasound at five weeks it would probably look something like this one on the right. Here by the red arrow you can see the dark, round yolk sac, which is about the size of a pea. In this case the baby is still too small to be visible, but sometimes the baby can also be made out at this time.
During this week limb buds for your baby's arms and legs will appear and the starting blocks for facial features begin to take shape. The already beating heart is now finding a more settled rhythm and developing its interior chambers, and rudimentary blood is beginning to be moved through the main vessels.
Other major organs like the kidneys are beginning to form, as are the early structures of the eyes and ears. The embryo is also now developing the tissue that will form the baby's vertebra.
What's happening with mum?
People often talk about women glowing during pregnancy, but at this early stage you're more likely to find your skin and hair changing for the worse. Your hair might become lank and greasy and you might well find that you have more spots than you did as a teenager!
Higher progesterone levels can affect your digestion and while most women expect bouts of morning sickness, you might not be prepared for the likely indigestion, constipation or wind that may already have started. Peppermint tea can often help settle a stomach but if you take any medicines then make sure that they're safe for use during pregnancy – many indigestion tablets are.
NB: All pregnancies are different and fetal growth rates vary, this is meant only as an approximate guide to development. If you have any concerns about your developing pregnancy then speak to your doctor.
Find out more about what's happening to your pregnant body
Bleeding in early pregnancy
It can be very scary to experience, but it's very common and doesn't necessarily mean there's a problem with your pregnancy make sure you know more about bleeding in early pregnancy.
Being pregnant affects everyone differently, but there are a number of very common pregnancy symptoms that you may experience in the early weeks.
Wind and bloating?
It's very common for pregnant women to experience excessive wind and bloating in their first trimester. If you're affected read why and what you can do about it and how to change your diet to stop wind.
Crucial time to avoid alcohol
Weeks 6 - 12 are the most crucial weeks for your baby's development and the period when it's most important that you avoid alcohol. Here's why.
Coping with morning sickness
It's one of the most common pregnancy complaints and can vary greatly in degree and duration of suffering. Here's what you need to know about coping with morning sickness and how your fruit bowl could hold the key to stopping you feeling sick or even this mobile phone app. Find out about what other discomforts bug mums to be during pregnancy and the embarrassing pregnancy discomforts no one wants to talk about.
Essential pregnancy dos and don'ts
Make sure you get your pregnancy off on a healthy track by following our essential tips for a healthy pregnancy.
Taking folic acid
Besides cutting out toxins, the most important step you can take as a newly pregnant woman is to make sure that you're taking 400mcg of folic acid daily. Here's how and why and when you need to take folic acid.