Pregnancy Week by Week

First Trimester

Second Trimester

Third Trimester

Watching your pregnancy week by week is an exciting way to understand how you baby and body is developing. Week by week during your pregnancy the stages of your baby’s growth in the womb are measured. When looking at a pregnancy week by week the first and second trimesters are 13 weeks long, and the third trimesters are 14 weeks.

Week by week each pregnancy brings new changes for you and your growing baby: morning sickness in the first trimester, because of pregnancy hormones; in your second trimester, you'll be lucky enough to feel your baby move in the womb for the first time; and in the third, you might feel breathless as your baby begins to take up rather a lot of space, pushing everything else out of the way. These are all part and parcel of pregnancy week by week journey: think about the changes changes your baby has to undergo during the nine months! Starting as an embryo no longer than 2mm in length at five weeks, by the time you reach 36 weeks, your baby is fully mature and up to 50cm long.

A normal or 'term' pregnancy typically lasts for 280 days, or if you are looking at your pregnancy week by week then it would be 40 weeks (which is roughly nine calendar months) and is calculated from the first day of your last menstrual period, or LMP. The reason for this is because the exact date of conception can be hard to pin down, although in women with regular four-weekly cycles, conception has usually occurred two weeks after your LMP. You'll find that healthcare professionals refer to completed weeks of pregnancy. Again, they calculate this from the first day of your LMP.

Pregnancy isn't 'one size fits all'. Every pregnancy is different, and your baby will develop at his/her own pace. Making regular antenatal visits, and talking to your healthcare professional will help to reassure, and to ensure that you and your baby get the care that you both need.