The dates you were given on the previous page are for 37 and 42 weeks pregnant, and your baby is likely to arrive between these dates. You may have been given a single date, and a few babies will arrive on their due date, some will be born before that date, and many will be born after it. Focusing on a single date can make the end of pregnancy quite stressful, so it can help to be prepared for your baby to arrive some time after the first date, and many women find that focusing on the last date as a time by which you have a good chance of having given birth allows them to enjoy those last week of pregnancy.
About 90% of pregnancy will naturally last between 37 and 42 weeks, and because of this that it is referred to a normal term pregnancy.
Naturally about 5% (1 in 20) pregnancy will last less than 37 weeks and 5% (1 in 20) will last more than 42 weeks.
This normal distribution of gestation is the same as you see with other genetic differences, foot size, birth weights, adult heights. Women in the UK have an average height of 1.62m, with 5% being shorter than 1.50m and 5% taller than 1.74m. Less than 1% of women will be taller than 1.79m, although the number of women taller than this is small, there is nothing actually wrong with being that tall.
The same is sort of distribution is seen with normal pregnancy, with about 1% of pregnancies being longer than 43 weeks. There is nothing wrong with these pregnancies they are just a normal genetic variation. Pregnancy of 44 or 45 weeks are even more unusual, but again are just a genetic variation.
Many women with longer pregnancies find that everyone is asking whether they have had their baby yet, and that health care workers start to suggest inducing labour. For some women this will be the right decision, but it is important to know that this is your decision to make. For more information you might like to have a look at the AIMS book "Inducing Labour, Making Informed Decisions" which is available from the shop.