Your weeks of pregnancy are dated from the first day of your last period.
This means that in the first 2 weeks or so, you are not actually pregnant – your body is preparing for ovulation (releasing an egg from one of your ovaries) as usual.
Your "getting pregnant" timeline is:
- day 1 is the first day of your period
- day 14 (or slightly before or after, depending how long your menstrual cycle is) you ovulate
- within 24 hours of ovulation, the egg is fertilised by sperm if you have had sex in the last few days without using contraception
- about 5 to 6 days after ovulation, the fertilised egg burrows into the lining of the womb – this is called implantation
- you're now pregnant
You at 1 to 3 weeks
The first thing most women notice is that their period does not arrive.
The most reliable way of finding out if you're pregnant is to take a pregnancy test.
Once you think you could be pregnant, it's important to get in touch with us to start your pregnancy (antenatal) care, via our self-referral form.
Your 1st trimester
The first trimester begins on the first day of your last period and lasts until the end of week 12 and a lot is happening for both you and your baby during these three months.
The fertilised egg rapidly divides into layers of cells and implants in the wall of your womb where it carries on growing. These layers of cells become an embryo, which is what the baby is called at this stage.
During this trimester, your baby grows faster than at any other time. By six weeks, a heartbeat can usually be heard and by the end of week 12, your baby's bones, muscles and all the organs of the body have formed.
Read more about what to expect in week 1 to 12 of pregnancy
Your 2nd trimester
The second trimester of your pregnancy is from week 13 to week 28 - roughly months four, five and six.
As well as feeling and looking more pregnant during these weeks, you may also have more energy than you did in the first trimester.
As you go through the second trimester, you’ll gradually see your 'bump' grow and later you'll start to feel your baby moving.
Read more about what to expect in week 13 to 27 of pregnancy
Your 3rd trimester
The third trimester of your pregnancy is from week 29 to week 40 - months seven, eight and nine.
Feelings at this stage of pregnancy tend to go from tiredness and worry to excitement about the baby.
Your baby continues to grow, and as the third trimester progresses they'll have a better chance if they're born early. You’ll have more checks with the midwife in the third trimester, because it’s important to keep an eye on your and your baby’s health.
Read more about what to expect in week 28 to 40 of pregnancy
The NHS start4life week-by-week pregnancy guide is full of essential information. From early pregnancy symptoms to how your baby is growing and developing, you'll find it all there.