First trimester: weeks 1 to 12

You're pregnant: congratulations! The first weeks of your pregnancy are a vital time as your body gets busy building a baby. How exciting!

Weeks 1-12 infographic

First trimester: key stages

The first trimester begins on the first day of your last period and lasts until the end of week 12. This means that by the time you know for sure you're pregnant, you might already be five or six weeks pregnant!

A lot happens during these first 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. At this point, your baby looks like a tiny human being and is now called a fetus. He or she will even be practising swallowing!

When am I due?

Find out your due date using our due date calculator!

When will I see a midwife?

Your first midwife appointment (also known as antenatal appointment) is the 'booking' appointment. This usually happens between week 8 and 10 of your pregnancy. Find out how to register with a midwife and when your appointments will be here.

Keeping your baby safe

There are some things that you can do during pregnancy that have an effect on your baby. Find out about them by clicking the link below.

Find the complete list of pregnancy dos and don'ts (and reasons why) here

Not sure whether you are pregnant?

Find out about the symptoms that mean you may be pregnant here.

Your physical and mental health in pregnancy

We also have lots of useful tips for coping with everyday pregnancy niggles. It’s common for women to experience symptoms such as morning sickness, cramp and indigestion during the first trimester. 

Don't forget that your mental health is just as important as your physical health. It's normal to feel some anxiety and stress but it shouldn't be ongoing. If what you’re feeling isn’t normal for you, talk to your GP or midwife about it. They are there to help. 

Exercise, such as yoga, has been shown to reduce anxiety and is a great way to stay active during your pregnancy, too.

Read more about mental wellbeing in pregnancy

Read more about diabetes and pregnancy

Read more about pregnancy with a high BMI

Read more about exercise and pregnancy

Read about the symptoms to look out for in pregnancy

Track your baby's development

Sign up to a free pregnancy email from our midwives to track your baby's development and give you reminders of all you need to know through the nine months of pregnancy. Click here to sign up.


Find out more about the first trimester


NHS Choices. Your pregnancy week by week (Page last reviewed: 28/02/2017 Next review due: 28/02/2020)

Macdonald S, Magill-Cuerden J (2012) Mayes’ Midwifery, 14th edition, London, Ballière Tindall

NICE (2008) Antenatal care for uncomplicated pregnancies, NICE Clinical Guidelines 62. National Institute for Health and Care Excellence

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    Last reviewed on June 28th, 2018. Next review date June 28th, 2021.

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    Please note that these comments are monitored but not answered by Tommy’s. Please call your GP or maternity unit if you have concerns about your health or your baby’s health.
    • By Suzan (not verified) on 2 Oct 2019 - 17:26

      Im 42 years On December last year while I was 5 weeks pregnant then I started to bleed, went to hospital doc took some lab blood to check hcg only to find Iit was ectopic. Last period july now im 9 weeks one day iam woried no symptoms at all, i took my home test 3 days before my period was positive even today still positive, I'm scared it should be ectopic again I'm afraid even to go hospital to be dissapoited, pls help me

    • By Keisha (not verified) on 25 Sep 2019 - 10:13

      I had sex with my husband the 6 of August 2019 and my period came that same day then my period came back on the on the 1th of September and lasted 3 day but its was Brownish. My breast has been swollen and I am weeing more often than I am use to and I feel sick most of the time. I done a test early in august and it was negative so I dont understand if this is harmone or I am pregnant

    • By Anonymous (not verified) on 22 Sep 2019 - 18:28

      Am confused

    • By Radhika (not verified) on 22 Sep 2019 - 06:04

      I’m kind a scare that my first baby pass away on due date and it’s been 10month. I found out I’m pregnant again and I’m so scare, would that be possible if the first die and second will have problems? Should I ask anything to my OBGYN ???please advice!!!!

    • By Anna (not verified) on 8 Oct 2019 - 01:07

      Hi hun this happend to me and i fell pregnant a few months after and it my baby was fine so try not to worry to much just try to enjoy your pregnancy hope all goes well for you

    • By Smith (not verified) on 15 Sep 2019 - 23:01

      Hi my name is smith I jjust want to know if I use heroine and my wife won’t even smoke is there any problem with pregnancy?

    • By Risha (not verified) on 4 Sep 2019 - 09:13

      So i missed my periods last month and i took the test when i got my periods for the next month. The test showed negative but that still doesn't explain the missed period. What should i do?

    • By Ms Goode (not verified) on 6 Sep 2019 - 23:22

      The same thing happened to me. I went to my doctor and took a blood and urine test.... it came back positive. Check with you regular doctor

    • By Sherica Scott (not verified) on 17 Sep 2019 - 03:34

      I would encourage you to see a doctor it could be a sign of pcos, I have the condition and in some causes it cause miss periods.

    • By Katherine (not verified) on 29 Aug 2019 - 05:58

      Okay so last week my boyfriend and I had unprotected sex it was Friday the 9th and I have been having symptoms. Like I just got off my period the day before but now I am very sleepy in the morning and I've been peeing more and more I also can't really lay on my back because it hurts. and I had stomach pain and headaches I've not to be I've been blotted I haven't vomited but I've been nausea and dizzy are these signs of pregnancy.

    • By Anonymous (not verified) on 5 Sep 2019 - 07:52

      It seems you have got pregnancy you have early symptoms of pregnancy. For

    • By Zella (not verified) on 11 Sep 2019 - 12:18

      S of course. U might be if u haven’t experienced any of these symptoms earlier before getting your periods

    • By Lungile (not verified) on 9 Aug 2019 - 03:41

      Hi I'm a woman of 34 my questions is yesterday I went to the local clinic for check up.I'm so confused and stressed at the same time course my due date is 12 of August so they said to me I must go to the hospital to get the abortion pill to make me deliver the baby so first how dangerous it is course I never done that in my in tiyer life I'm so scared.please help me.

    • By Mom of 2 (not verified) on 15 Aug 2019 - 03:25

      I would not recommend getting the abortion pill to make the baby deliver. Your baby knows when it needs to be born. The due date is just an estimate to make you aware that baby will be coming around that time. I would wait a little while longer (if you have not already had baby).

    • By Anonymous (not verified) on 6 Aug 2019 - 20:43

      I did not receive my next contraceptive injection when it was due,my husband and i decided to try for a second child, my injection was due 10 june,since then weve been trying maybe every second night, ive started feeling tired and started getting heartburn as well, there is some nuasia but not much,is it to soon to take a pregnancy test,i must add while on the injection those last weeks before the next one i was on antibiotics aswell

    • By Stephanie (not verified) on 30 Jul 2019 - 12:33

      I got my period last month but this month i only bled for 2 days straight which is unusual and light since then I've had sore breasts, heartburn and very strong backpains could I be pregnant

    • By Tom (not verified) on 6 Aug 2019 - 11:23

      What you experienced most probably is called implantation bleeding. the signs are of it. Do a home pregnancy test

    • By Lizzy (not verified) on 29 Jul 2019 - 11:52

      I took my last period on the 20th of June so with calculations midwifes think Iam 5 weeks but my stomach is massive Iook about 12 weeks what could this be

    • By Anonymous (not verified) on 28 Jul 2019 - 20:25

      I am pregnant,

    • By Nadia (not verified) on 16 Jun 2019 - 11:23

      My last period were on 6th may got a positive result i have a bad pain on my left always feel like there is something on my left side

    • By Sarah Barnes (not verified) on 10 Jun 2019 - 21:49

      Is it too soon to have sex after having a 10week old baby?

    • By Mallory (not verified) on 27 Jun 2019 - 02:54

      I believe usually healthcare providers advise to wait 4-6 weeks after delivery but you should probably double check with your own dr to verify all is well down there

    • By chantel (not verified) on 9 Jun 2019 - 00:28

      l last saw my period mid feb 2019 and had unprotected sex late feb to early march.Since february l havent had my period yet .my belly is slightly bigger and breasts without any other signs of being pregnant.l have not taken any test.can l be pregnant considering that my cycle is not stable at one time l went for 4 months without my period but l was not pregnant.

    • By Tracy (not verified) on 6 Jun 2019 - 07:05

      Hey im 18 years old . My last period was on may 4th , I was supposed to get my period on june 1st instead i have brown discharge for 6 days i took a pregancy test today and it came out negative but now im having pain around my ovaries can someone help mee

    • By Anonymous (not verified) on 7 Jun 2019 - 11:10

      I would contact an OB for hcg levels if you are pregnant. I mean you should regardless especially if you have pain. But typical Implantation bleeding only last a day or so

    • By Denis mugagga S... (not verified) on 15 Jun 2019 - 20:18

      Sorry about that dear u need to see a gynaecologist coz u could be having STIs

    • By Jc (not verified) on 18 Jun 2019 - 08:58

      Hey the exact same thing happened to me and I’m still waiting for my period, how did you turn out??

    • By Marcia (not verified) on 21 Jun 2019 - 14:31

      The brown Discharge you mentioned could be implantation bleeding. Since you posted this well over a week ago, you should take another pregnancy test if you haven't had your period yet. The pregnancy hormone often isn't detectible until after your missed period- so it would be wise to check again.

    • By Victoria (not verified) on 4 Jun 2019 - 23:05

      Hi. I had my 1st sex ever(un-protected) on the 6th of may(the week am suppose to have my period) so i did'nt see my period untill 24th of may. A week after i'd been feeling dizzy,having severe headache and sleepy every morning. But it only lasted a week. Have done a home test but it's not giving results. Could i be pregnant? Cause my Guy did'nt realease on me.

    • By Anonymous (not verified) on 7 Jun 2019 - 11:14

      If you got your period the 24th of May there’s really not a way you went through your mensural cycle, Ovulated, conceived and then implanted in that short of a time. Can’t do much if the tests are coming back negative too and that he didn’t inside of you.

    • By Orrelia (not verified) on 4 Jun 2019 - 08:43

      I have the worst morning sickness ever cannot keep fluids down for the past two to three days i have not been drinking any fluids and i have stomach cramps,headeaches and dizziness, i feel tired and i dont want to eat although i feel hungry because i vomit. I peeone or twice a day if i am lucky is this normal or should i be worried.

    • By Marie101 (not verified) on 3 Jun 2019 - 18:34

      Am I supposed to have pelvic pain first trimester?

    • By dennisonbritany... (not verified) on 27 May 2019 - 02:08

      I have heavy irregular periods issues and on birth control implant and missed 2 birth control pills from three weeks ago and missed 2 birth control pills two weeks ago and had sex last May 16 2019 few hours after stopped period then after had sex went in bathroom and wiped my private area and found just very tiny drop bleed then an hour stopped and don't have period anymore after that since, I took home pregnant test last week on May 19 2019 and came out negative, I still feel tiredness, have those headaches, weakness, cramps for two days, yesterday and today. And my private area is smell odd because it smell different, have morning sick every night, have nauseaous. And have been moody swing. one min grouchy, then laughing, then annoyed by others. And haven't have any period yet. So, am I possible pregnant? And my birth control implant is bended. Because it have been pains in my right upper arm where my birth control implant in.

    • By Gaga (not verified) on 25 May 2019 - 11:07

      I am 7 weeks pregnant. But, from 2 today, i have discharge with mixed blood when i wipe with toilet paper. I am very much worried

    • By Sarah (not verified) on 23 May 2019 - 11:53

      I am just over 4 weeks pregnant I have had some bleeding and cramping last night but this morning there isn't blood it's just a brown colour with some cramping, what does this mean

    • By Kerri (not verified) on 17 May 2019 - 08:45

      I missed my period for 7 days. I did a urine test and it said that I am 2-3 weeks pregnant. I then did a blood test which confirmed that I am pregnant with a HCG count of 169. The day after my blood test, I started my period. The doctor advised I must do blood tests again in 4 days time to check if my HCG count has increased. 4 days are still so long and its making me anxious. Am I having my last period because its early days or have I had an early miscarriage?

    • By Anonymous (not verified) on 30 May 2019 - 21:52

      I'm having same situation. 7days late and 2 positive pregnancy test . Am I pregnant or should I wait more for my periods to come back?

    • By Anonymous (not verified) on 7 Jun 2019 - 11:06

      If the pregnancy test came back positive they knew most definitely pregnant

    • By Baby (not verified) on 14 May 2019 - 17:59

      hi.... I had some signs of pregnancy during the 2nd week of April.... so I went for a pregnancy test via blood test nd it came out positive.... but on the same day I I got the test for a positive pregnancy result test my mestratution started that lasted for 4days... confused tho.... I started monitoring myself,after the menstrual period... so I found out I sleep too much, feel week very often, eat too much, have sore breast .... now the date of that the last period was 12-15... now in may the am having cramps, light spotting of blood.. am confused... please help

    • By Jas (not verified) on 4 May 2019 - 03:44

      I went to the hospital and they gave me a urine test it showed I was pregnant they then drew blood it was called a titer they checked for my HCG levels and my baby blood type well I was told it's very little fetus growth and my HCG levels was only 100 but they didn't tell me how far along I was and they want me to come back in three days to repeat the titer well I went to the hope center and they told me I was four weeks pregnant but they went off my lmp I had a miscarriage before does that mean that's what this is reason why my levels are only 100 and why the ER couldn't tell me how far along I am only styoms I have is sore breast peeing alot eating alot sleepy and cramps but today only had peeing alot eating alot and little sleepy no cramps

    • By Megan (not verified) on 3 May 2019 - 19:06

      I had started my period april the 4th it lasted 4 Days then i started again on april 29th it only lasted 3 days
      Could i be pregnant i have taken several pregnancy test and they keep showing faint positive lines? I havent been feeling like myself lately

    • By Megan (not verified) on 3 May 2019 - 19:03

      I had started my period april the 4th it lasted 4 Days then i started again on april 29th it only lasted 3 days
      Could i be pregnant i have taken several pregnancy test and they keep showing faint positive lines? I havent been feeling like myself lately

    • By Anxious Mum (not verified) on 1 May 2019 - 23:29

      Hello, I am 40 year old, have had three ( nearly four) failed pregnancies. Had two miscarriages and an ectopic ( with a tube removed). I am 6 weeks 5 days pregnant now, my hcg levels were slow rising with 2900 and 3300 in 48 hours. Scan revealed gestational sac but no yolk sac or embryo, also sac marked as irregular at 7 * 4 * 7, scan was hard and painful as they state visibility was poor due to its position, not sure what that means.
      Can you please advise?

    • By Scared (not verified) on 29 Mar 2019 - 00:03

      I’m having what feels like a period and they look at the baby today and it was fine. Have you heard of this before at 12 weeks?

    • By bria (not verified) on 12 Mar 2019 - 04:34

      this is every helpful. I will keep using this link.

    • By Jessy (not verified) on 10 Mar 2019 - 09:45

      Me and my partner had sex one month back. 1 week after that, I started feeling cramps,giddy and tired,back cramps.i went to doctor and took some prolactin level was 55..Now I got my periods which was not heavy like regular periods, that to for only 2days with out any severe was light bleeding than I pregnant?

    • By Blessing (not verified) on 10 May 2019 - 16:41

      I am not sure but think you are. Women who are pregnant have the prolactin levels btw 34 to 386 ng/mL. You might want to confirm from your doctor.

    • By Maria (not verified) on 18 Feb 2019 - 09:43

      My breast has been hard since the last week of December. My normal mensuration came on the 20/11/2018 but in December and January it as been very light and only two days or less than. I have been having several pregnancy signs could I be pregnant cause I have done home test but it comes out negative

    • By Midwife @Tommys on 21 Feb 2019 - 12:43

      Hi Maria, Thank you for your comment.

      As it has been a couple of months since your last period, it would be advisable for you to see the GP. You are getting negative pregnancy tests but you are still not having periods only spotting. The GP will be able to take some bloods to check your hormone levels and if you need a referral then he can do this. Take Care, Tommy's Midwives x

    • By Lizzy (not verified) on 14 Feb 2019 - 21:43

      I'm four months pregnant but my Tommy is not coming out pls what can I do

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