One of the first things you will have to deal with as a pregnant woman is how far along you are.Both because it must be used to calculate when you are due to give birth, but also because all your doctor and midwife visits and scans will be calculated based on how far along you are in your pregnancy.
Week 1 starts before you are pregnant
It may come as a surprise to some, but the countdown to your pregnancy actually starts on the first day you get your period. So, on day 1 of your cycle. This also means that fertilization, which occurs during ovulation, takes place around two weeks later (depending on the length of your cycle). When you should have your period and take a positive pregnancy test (see our large selection of pregnancy tests here), you are therefore 4+0 weeks along if you have an average cycle of 28 days.
Many may be a little confused by this way of counting the weeks of pregnancy because you are not pregnant on the first day of your period, but it is nevertheless the way that the weeks of pregnancy are counted.
When the due date moves after a scan (and the new date sometimes doesn't make sense at all compared to when you had sex or were inseminated)
When you have a positive test, you will quickly start to calculate how far you are. Let's say your cycle was 28 days and you took a test on the day your period was due. Then you will calculate that you are 4+0 weeks along and book an appointment with a doctor and calculate your due date based on that.
Your final due date is determined when you come for a nuchal fold scan in weeks 11+1 to 13+6 (read more about when to see a doctor, midwife and scan here: link: When to see a doctor, midwife and scan during the pregnancy?)
For the nuchal fold scan or for a possible early scan, the doctor/midwife will measure the fetus from the top of the child's head down to the bottom. The measure is called Crown-Rump-Length, and from this measurement you will be able to tell how far along you are and when you are due. You will also have this measurement carried out if you go for an early scan. Here, however, the due date will not be final. This will only be finally determined for the nape scan.
When you are moved forward or backward in the weeks of pregnancy
For the early scan or for the nuchal fold scan, you may well experience being moved several days forward or back. And sometimes the new date doesn't quite make sense compared to the date you know you last had your period or sex/was inseminated. But this is because your pregnancy only begins to develop once the fertilized egg has settled in the uterine cavity. This walk can take from a day to a week without it being abnormal.
This also means that you may experience that you are further or shorter in your pregnancy than expected, because the journey may have taken shorter or longer than expected. If, for example, the egg has spent a week on its journey through the fallopian tube, you may therefore also risk being shorter in your pregnancy than you had expected, and if, conversely, it has gone quickly, you may be further along.
See our large selection of pregnancy tests here: Graviditetstests – Gravidtid