Pregnancy week by week
What is a trimester?
People often talk about pregnancy as being nine months long. In fact it’s usually slightly longer than this. Your pregnancy is measured from the first day of your last period rather than the day you actually conceived.
A pregnancy generally lasts around 40 weeks, and your dates are referred to in weeks because this is more accurate than talking in months.
Your pregnancy has three phases, called trimesters, and each trimester is about three months long.
Each trimester has its own mix of highs and lows, and you can find out what to expect in this pregnancy calendar. The information in the calendar may be helpful for the people close to you as well.
Confused about pregnancy weeks? Wondering whether to count from the day you conceived or your last period? Discover how to count your pregnancy in weeks and months on the BabyCentre website. You can also join your BabyCentre birth club to meet others due at the same time as you, share stories, and swap tips and advice.
In this section
Finding out you’re pregnant
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