4 weeks gestation is really the first big milestone along this path to parenthood, at it's usually in this week that home pregnancy tests can pick up traces of human chorionic gonadotropin (HCG), produced by the rapidly growing placenta.

Buying a pregnancy test is a big deal, and taking it even more so! In the space of just 3 short minutes (although it can feel like hours!) your life could be changed forever. It's recommended that you take a test no earlier than the day your period is due, although some extra sensitive tests claim to be able to accurately confirm pregnancy up to 4 days before the expected date of your next menstrual cycle.

Baby: What's Happening?

Your baby may not look particularly different this week, still appearing as a tiny ball of cells, about 3mm in diameter; that's around the size of a small seed. However, there's been some big changes in the last 7 days, including the embryo dividing into 3 distinct sections; that which will form the central nervous system, that which will form the circulatory system, and that which will form the respiratory and digestive system.

The cell cluster itself will complete the implantation process during week 4, which is the attachment of the fertilized egg into the walls of the uterus. The high levels of estrogen and progesterone in your body at this time keep the wall lining thick and healthy, which is essential not only for holding on tightly to the cells and keeping them safe, but also for providing nutrients as the placenta isn't quite ready for this task just yet (but it's been working overtime and will be very soon!)

You: What's Happening?

If you don't already know you're pregnant, you're probably expecting your "time of the month" at the end of this week. You're probably also experiencing the classic tell-tale signs of menstruation, such as swollen and tender breasts, mild stomach cramps and irritability. These symptoms can all be caused by hormonal imbalances in the body, and can also be some of the signs of early pregnancy.

Week 4 can be particularly sneaky, as an estimated 25% of women experience implantation bleeding, which can present itself in a very similar fashion to the start of your period, leading many to believe they're not pregnant when they really are.

Implantation bleeding generally happens during week 4 (although it may happen as early as week 3) and is caused by the cells embedding themselves into your uterine walls. Those walls are thickly lined with blood and tissue that has been building up over the past month. When the fertilized egg burrows into those layers, it can dislodge a little bit of this lining, which is then passed in the same way as menstruation.

Once you've gotten over the initial shock of discovering you're pregnant (the overall shock never goes away!), you may want to think about contacting your Doctor. Don't panic about this, it isn't urgent as your first antenatal appointment won't be until at least 10 weeks gestation, but it's best to get yourself into the system.

Your Doctor may wish to see you, or you may simply be asked to complete some paperwork so you can be referred for antenatal care. If you do need to make an appointment, you will probably have your height and weight checked, and be asked about any existing health issues and any past pregnancies. You may have a blood test to confirm the pregnancy, and to rule out any blood borne diseases.

Handy Hints

Now's the time to stock up on sample containers! At every pregnancy-related appointment you attend from now on, you'll be asked to bring a urine sample so it can be checked for glucose and protein. There is no doubt you will be an expert at peeing in a tube by the time your baby's born! Luckily, these tubes can be picked up for a small cost at many drug stores, and may even be handed out for free at some clinics.

Implantation bleeding is usually a pink or brown color, much lighter than a real period, and tends to appear as small spots in your underwear, rather than being a heavy flow. If you have had a positive pregnancy test, or suspect you may be pregnant and have bright red or heavy bleeding, it's worth getting yourself checked out, as bleeding during pregnancy is not normal. You may find wearing a panty liner is handy for keeping an eye on blood loss.

If you've taken a pregnancy test during week 4 and had a negative result, but your period doesn't start when you expect it to, try leaving it a few days and then testing again, as it could be that your HCG levels just weren't high enough the last time you tested.