First trimester: weeks 1 to 12

The first weeks of your pregnancy are a vital time as your pregnancy gets established. While you get used to being pregnant, your body is busy building a baby!

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!

Lifestyle changes in the first trimester of pregnancy

You may need to make some lifestyle changes now that you are pregnant. Find out which foods and medicines you should avoid to keep your baby safe and healthy here. You’ll also need to cut out alcohol and smoking, and cut back on your caffeine intake.

Get your free guide to healthy eating straight into your inbox.

Try not to worry if you smoked or drank alcohol before you found out you were pregnant. Now that you know, you can take steps to look after yourself and your baby.

Get help to stop smoking here.

You can also find lots of useful tips on coping with everyday pregnancy niggles such as morning sickness, cramp or indigestion.

Don't forget your mental health as well as your physical health! It's normal to feel some anxiety and stress but it shouldn't be ongoing.

Find out more about emotional changes in pregnancy here.

Find out more about the first trimester

Sources

1. NHS Choices (2012). “Your pregnancy week by week”. National Health Services: Choices. Accessed online on 02.02.2015: http://www.nhs.uk/conditions/pregnancy-and-baby/pages/pregnancy-week-by-week.aspx#close Page last reviewed: 22/07/2014. Next review due: 22/07/2016

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

3. NICE (2008). “Antenatal care: NICE clinical guideline 62”. National Institue for health and care excellence 2008; accessed online on 15.01.2015: http://www.nice.org.uk/guidance/cg62/resources/guidance-antenatal-care-pdf (last review August 2014). 

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Last reviewed on April 1st, 2015. Next review date April 1st, 2018.

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Comments

  • By Anonymous (not verified) on 13 Mar 2017 - 15:57

    HEY THERE, MY friend Says she missed her 2nd depo shot on 13th Feb and on 24th Feb she had unprotected sex,so she scared she might be pregnant is the any chance of her to be pregnant?????

  • By Midwife @Tommys on 13 Mar 2017 - 16:36

    It is really important when using Depo-Provera injections as a form of contraception that the injections are given on time. If it is overdue there is a possibility of a pregnancy . There is good information available on the sexual health charity website. http://www.fpa.org.uk/contraception-help/contraceptive-injections . Hope this helps

  • By Anonymous (not verified) on 9 Mar 2017 - 09:16

    I've been on the nur isterate injection for 6 months. I stopped it now 2 months. I've been getting symptoms of pregnancy like very sore breasts nausea no vomiting and stomach cramps.. My last period was on the 13th of Feb... I tested 2 days back and got a negative result was it to early to test
    Could I be pregnant?

  • By Midwife @Tommys on 9 Mar 2017 - 10:08

    Hi, Yes, it is too early to confirm a pregnancy if your last menstrual period was 13/2/17. If you are wanting to become pregnant don't forget to look at our link for preconception care. https://www.tommys.org/pregnancy-information/getting-pregnant/are-you-ready-conceive
    BW Tommy's midwives

  • By Anonymous (not verified) on 8 Mar 2017 - 16:23

    Hi, I am around 6 weeks pregnant and I occasionally get light craping pains in my lower back and around my hips, is this normal? I have no bleeding. This is my second pregnancy but the 1st was 8 years ago and it's difficult to remember.

    Another question - we have guinea pigs kept indoors, do these pose a threat to an unborn baby?

    Thanks

  • By Midwife @Tommys on 9 Mar 2017 - 09:53

    Hi, Mild cramping pains are not unusual in pregnancy. Each woman and each pregnancy is different. It is reassuring that you have no bleeding. Try gentle exercising and keep yourself moving.
    There is no reason to be concerned about guinea pigs although it would be good practice to wear gloves when cleaning them out and also to ensure excellent hand hygiene after handling them. Our link on toxoplasmosis explains why cats are thought to be the animals that transmit this infection in their faeces. https://www.tommys.org/pregnancy-information/i%E2%80%99m-pregnant/antenatal-care/infections-avoid-pregnancy/toxoplasmosis-pregnancy
    Hope this helps. Tommy's midwives

  • By Anonymous (not verified) on 8 Mar 2017 - 10:45

    Hi, i have been off my birthcontrol two weeks ago and me and the hubby had grown up games a day before i stopped taking my tablets, last week i had no bad feelings or symptoms at all but this week i feel rough as hell, i have had headaches been more moody been over sexual (tmi) had felt sick yesterday morning (not had that today). i would just like to know if i should buy a test or leave it down to my bc, i have read that some women it could take months/years to conceive and others within the month of coming off them, please help me someone lol.

  • By Midwife @Tommys on 8 Mar 2017 - 14:48

    Hi Jess,
    I wonder if the symptoms you are experiencing are side effects of coming off the pill.
    Certainly a peak in interest in sex is really common after coming off the pill as in your natural cycle there is a surge in testosterone. (Women talk about having a lower sex drive on the pill).
    You could also be more moody after stopping it. Some women also report headaches, breast tenderness and nausea.
    After stopping the pill you can technically ovulate within a week and sperm can live in a woman's body for 5 days so if you weren't using an alternative form of contraception you could be pregnant. My advice would be to buy a pregnancy test and test when it is 3 and a half weeks since you had sex when coming off the pill. Your periods may take a little while to regulate (1-3 months approximately) so even more reason to have an alternative form of contraception if you aren't quite ready to start trying for a baby.
    I hope this helps.
    Tommy's Midwives

  • By Anonymous (not verified) on 7 Mar 2017 - 13:28

    Hi, I'm 8 weeks & 2 days pregnant although I don't feel pregnant! Is this normal?

    I'm also sleeping for around 16 + hours at a time over the last few days, whereas I was only getting about 2 hours sleep in the weeks prior. Is 16 + hours of sleep & lack of energy normal at this early stage?

    Thank you

  • By Midwife @Tommys on 7 Mar 2017 - 14:38

    Hi,
    Congratulations on your pregnancy! This early stage can be very tiring and every pregnant woman experiences different symptoms which can vary hugely and some never really get any noticeable symptoms. Sleeping a lot more can be normal and part of early pregnancy, however it can also be a sign of low iron levels and sometimes a thyroid problem, if this has been continuing then I would recommend you contacting your GP or midwife. If you have had your booking appointment then they should have taking some blood tests from you, if you chase these up this will tell you your iron levels. If you have not yet had your booking then hopefully this will be soon. If you have any breathlessness or pain then I would advise for you to see your GP as soon as possible. I hope this helps, Tommy's midwives.

  • By Anonymous (not verified) on 15 Mar 2017 - 16:33

    Hi, Thank you for your above response.

    I've been for my booking appointment today & have left feeling totally confused......I had both an external & internal scan & they've said that I'm only 4 weeks pregnant (too early for the booking appointment checks) although checking when I tested posititve, it was 8 weeks ago.

    How is this possible - is something wrong?

    Thanks again for your help

  • By Midwife @Tommys on 16 Mar 2017 - 09:57

    Hi, I think i just replied to you on another page.
    You need to work out the date of the first day of your last menstrual period, and your average cycle length using our pregnancy calculator to estimate your gestation and current due date.
    Once you know this, please go back to your GP to discuss the results and get another date for booking and ultrasound scan. Sometimes dating pregnancies can be confusing, but it is important to know roughly how pregnant you are so that you receive the right care in a timely manner. Take care of yourself

  • By Midwife @Tommys on 1 Mar 2017 - 14:29

    Hi, thank you for your post. It sounds like the bleeding was a really frightening experience. I understand from your message that you went on to have an early scan and you were told that 'there was a pregnancy but it was not really formed' It is such a shock when you experience unexpected bleeding and then end up being scanned. In times of intense stress we don't retain information as we are in shock. Is there a plan for you to return to the hospital for another scan? In some instances it may be too early to detect a heartbeat and confirm a viable pregnancy so returning to be rescanned in 10-14 days can give more information as the developing embryo would be visible as would a heartbeat.
    I hope that this has been scheduled for you? You might like to look at this website for more information.
    http://www.aepu.org.uk/
    Please keep in contact and if you would like to talk to a midwife please contact us on 0800 0147 800 weekdays 9-5 pm
    Tommy's Midwives

  • By Anonymous (not verified) on 1 Mar 2017 - 13:23

    Good afternoon, I really cannot remember my last date for menstrual period, but I tested positive for home test on the 21st.of February. My last period was around the second to the last week in January, and I ovulate d around 4_7 of February. How old can it be?

  • By Midwife @Tommys on 3 Mar 2017 - 12:39

    If you have a positive pregnancy test I would suggest that you arrange to see your doctor. Without accurate dates the best way to date the pregnancy is to do an early pregnancy scan. Your GP will be able to arrange this for you. Best wishes from Tommy's midwives.

  • By Anonymous (not verified) on 28 Feb 2017 - 21:55

    Hi.. I found out i was pregnant a week ago 20th feb 2017.... Just two days ago, i saw blood whilst taking a shower. I rushed to the hsp and was giving injection to stop the blood. It has stopped now but the gyn after doing the ultrasound said there was a pregnancy but not really formed. I'm soo scared and dont know what to do

  • By Anonymous (not verified) on 28 Feb 2017 - 11:25

    I am 11weeks pregnant I seen my baby heartbeat but sometimes I feel like I am pregnant and at times I don't I have back pain and stomach pain where I can't sleep
    The doctor said I have a cyst over my ovaries

  • By Anonymous (not verified) on 27 Feb 2017 - 08:13

    hello.. my last period was on 25th jan 2017.. its been a month bt i havnt got my periods yet.. me n my hubby had intercourse on 7- 8-9-10 of this month... shud i go for a home pregnancy test?? or is it too early ??

  • By Midwife @Tommys on 27 Feb 2017 - 11:46

    Hi there.
    Using your last menstrual period date of 25th jan, and presuming you have a 28 day cycle, it is possible that you are approx 3 weeks pregnant and this would show up on a pregnancy test if you are pregnant. So it is worth going out and buying a home test. Some tests are more sensitive than others, so waiting another few days may be sensible in order for your pregnancy hormones to increase and show in your urine.
    Take care and good luck!

  • By Anonymous (not verified) on 26 Feb 2017 - 10:01

    hello am 8weeks pregnant but i have alot of pain in my stomach i was given medicines like paracetamol n bascopan but there is no change... i dont feel like eating anything i only take porridge..... the náusea is very strong even after taking medicine for it.... what should i do please

  • By Midwife @Tommys on 27 Feb 2017 - 10:27

    Hi there.
    Any abdominal pain, at any gestation of pregnancy, needs to be investigated as soon as possible. It would be a good idea for your GP to refer you to your local early pregnancy assessment unit so that you can have an abdominal scan and bloods taken to ensure the pregnancy is healthy. If your pain is incredibly severe, then you should go to a&e urgently in case the pregnancy is ectopic (growing in your Fallopian tube) which can cause a lot of abdominal pain and is incredibly dangerous to your health.

    Pregnancy nausea is very common and can come and go throughout pregnancy. There are various simple ways that you can try to ease the nausea. Have a look on our webpage for some helpful tipss to hopefully help you. https://www.tommys.org/pregnancy-information/im-pregnant/early-days-pregnancy/morning-sickness

    Please look after yourself!

  • By Anonymous (not verified) on 26 Feb 2017 - 09:23

    I found out I'm pregnant the 14 Jan 2017 when I was 3 weeks pregnant and I used two home tests got the same answer positive. I got my period the 9 of Feb for two days was abnormal flow and just dissaper. now I'm worried I lost this baby

  • By Midwife @Tommys on 27 Feb 2017 - 10:00

    Hi pregnancy mom
    It would be sensible for you to visit your GP asap to do another pregnancy test and to refer you to your local early pregnancy assessment unit if there is some concern about bleeding in early pregnancy. They may wish to take some bloods from you, and do an ultrasound scan to determine the gestation and health of the pregnancy. Please look after yourself.

  • By Anonymous (not verified) on 26 Feb 2017 - 08:02

    Hello, I have just found out I am expecting. Not really sure how far I am, I am going to the doctor this week, will they be able to tell me how far I am?
    I have been drinking alcohol and eating rubbish like sweets and chocolate and I feel terrible about it. I've cut it all out now since Friday but will this have done damage?

  • By Midwife @Tommys on 27 Feb 2017 - 09:54

    Hi Mjones
    Many women have exactly the same concerns as yours when they first find out that they are pregnant. Drinking alcohol in the early stages of pregnancy is something that many women worry and feel guilt about, but it is both unknown, yet unlikely to have caused any problems for the growing fetus. It is best that you completely cut out alcohol from now on. The occasional sweet treat like chocolate is not bad for pregnancy, everything in moderation is sensible. Please have a look at our webpage on diet during pregnancy so you can see what types of food and quantities are great for a healthy pregnancy.
    When you go to the doctor, they will ask for the date of the first day of your last menstrual period, to give an estimation of how many weeks you are. Then you will be referred for midwifery care and for your first ultrasound appointment where the gestation of your baby will be more accurate and an estimated due date will be given to you too. Please take care of yourself.

  • By Anonymous (not verified) on 18 Feb 2017 - 19:31

    pls help, I went to ultrasound scan and the doctor confirmed am 11 weeks pregnant and 3 days. but he said that I will put to bed on 27th June 2017. How possible it is. pls adivice

  • By Midwife @Tommys on 20 Feb 2017 - 09:34

    Hello and Congratulations on your pregnancy,
    Your message is a little unclear - please email on midwife@tommys.og or call our Pregnancy information line on 08000147800 for further advice.

  • By Anonymous (not verified) on 17 Feb 2017 - 18:07

    I'm abt 6weeks pregnant and I have dis abdominal pain and back pains as well not DAT painful but it makes me feel kinda awkward......and I have dis bitter taste in my mouth ...and m getting sick of DA pills m drinking

  • By Midwife @Tommys on 20 Feb 2017 - 09:45

    Congratulations on your pregnancy!
    I'm sorry you are experiencing lower back and abdominal pain - it is not unusual to experience some period like cramps in early pregnancy, but if they are painful, becoming more severe or causing you concern please contact your GP for a check up.

  • By Anonymous (not verified) on 16 Feb 2017 - 08:39

    I don't know how long i am, I'm pregnant and i have pain in my spanielccord please help is it normal? I tested pregnant on the 27/01/2017 and it was positive, on the 2/02/2017 i was bleeding on the 7/02/2017 it stopped until now and on the 13/02/2017 i tested it positive do you think it's normal?

  • By Midwife @Tommys on 16 Feb 2017 - 11:25

    Hi, I can understand your confusion and would suggest that if you have a positive pregnancy test on 13th that you see your GP. You may be referred to an early pregnancy unit for a scan and/or a blood test which will confirm whether or not you are pregnant.
    Hope this helps.
    Tommy's midwives

  • By Anonymous (not verified) on 16 Feb 2017 - 03:42

    Some few I did a PT In the lab n it showed positive But very faint line . I had alot of pain like cramp for over a week. Then I saw blood flow for 2days. I got worried although it's less than my normal flow. I tried doing a home test after d flow it's been negative. Should b worried? Been having headaches for a while. D pain down my abdomen has reduce. Pls am still pregnant.

  • By Midwife @Tommys on 16 Feb 2017 - 12:42

    Hi-Unfortunately it sounds like you have had a very early miscarriage. However if your abdominal pain continues or gets worse , it may be a good idea to see your GP.

    Hope this helps and do contact us if you have any other concerns

  • By Anonymous (not verified) on 16 Feb 2017 - 02:08

    Hello, I have been dizzy for about two and a half months now. I was always worried about what it was but tried to just wait for it to go away. For the passed two months I have experienced headaches daily and am nauseous every once and awhile. I started to develop a cough and some sinus drainage so I went to the doctor and they told me this is where the headache and dizziness are coming from and gave me antibiotics for a sinus infection. Two antibiotic doses later, the dizziness is ongoing. I have recently noticed my nipples have darkened and I almost fainted today. I have taken a few at home pregnancy tests and they all came back negative. I would have conceived November 5th. Is it safe to say it is time to get a blood test or could there be something else going on?

  • By Midwife @Tommys on 16 Feb 2017 - 11:35

    Hello, I am sorry to read that you have been feeling unwell. I would suggest that if this is on-going that you see your GP again. If your pregnancy tests are negative, this is because the pregnancy hormone hCG is not present in your urine and indicates that you are not pregnant. I hope you find some answers. Best wishes

  • By Anonymous (not verified) on 15 Feb 2017 - 17:43

    Hi,
    I've recently found out I am pregnant! I had the implant out on the 10 Jan 2017, tested on 7th Feb and it came up positive! Checked a few more times and all positive. Anyway I just wanted to know how to date this pregnancy? Would it be the day my implant was taken out? I am a bit worried about getting pregnant so quick after implant removal, just hoping it all goes ok.

    Thanks

  • By Midwife @Tommys on 16 Feb 2017 - 12:18

    Hi. There is no reason to be concerned about getting pregnant so soon after your implant was removed, but your GP may advise that you are seen in the early pregnancy unit in order to date the pregnancy. Best wishes from Tommy's midwives

  • By Anonymous (not verified) on 15 Feb 2017 - 06:37

    I have just found out im expecting but i keep getting pains in the lower part of my stomach almost like period pains is this normal

  • By Midwife @Tommys on 15 Feb 2017 - 13:24

    Congratulations on your pregnancy!
    I'm sorry you are experiencing lower abdominal pain - it is not unusual to experience some period like cramps in early pregnancy, but if they are painful, becoming more severe or causing you concern please contact your GP for a check up.

  • By Anonymous (not verified) on 9 Feb 2017 - 13:32

    Hi, I'm only 6 weeks and I've been in a lot of pain and feel like I'm going to pass out in the morning only due to have diarrhoea. Just want to know if this is normal. Has anyone had symptoms like this?

  • By Midwife @Tommys on 9 Feb 2017 - 15:31

    Hi. Sorry to hear that you are feeling unwell. Diarrhoea can be very distressing. Best advice is to ensure that you are drinking plenty to avoid becoming dehydrated and ensure that you wash your hands after going to the toilet. It is unlikely to cause a problem for the baby but if it persists beyond 48hrs, please see your GP. Regarding your pain, you don't say where this pain is. Please feel able to contact the midwives on 0800 0147 800 to discuss. Best wishes and we hope you feel better soon.

  • By Anonymous (not verified) on 9 Feb 2017 - 08:39

    Hi, im 6 weeks pregnant and last night when I laid down and touched my belly, I felt this weird lump about 2 inches away from the hip bone. The lump it's not painful in particular(sometimes on that side I feel a mild sharp pain that last 2 seconds) and it's about 6 cm long and feels quite thin. I don't have any bleedings or pain except some mild cramps on my lower abdomen. I'm very worried about this lump because (maybe sounds stupid) I'm afraid not to be an ectopic pregnancy. My appointment with my GP is in a few days, but this lump is keeping me worried. Can you please tell me what it might be? Thank you

  • By Midwife @Tommys on 9 Feb 2017 - 12:32

    Hi Congratulations on your pregnancy. There may be many reasons for this lump and it may go away on its own before you see your GP. It is reassuring that you don't have any pain or bleeding. If your symptoms change and you have pain or bleeding please see your GP or Early pregnancy unit.

  • By Anonymous (not verified) on 7 Feb 2017 - 16:32

    Only few days ago I found out I'm pregnant. Doing my calculations I should be about 5-6 weeks. What is concerned me is some quite mild cramps in my lower abdomen I'm feels them for the past few days. They aren't continuous, they start mostly when I standing up or working for few hours, but if I'm laying down they go away. I don't have any bleeding or back pain. I'm know the pains might be normal for the changes in my tummy, but I'm just worried not to be a sign of a miscarriage as I really wish to have this baby. I already made an appointment with my gp, but it's gonna be in two days, and the time it's absolutely killing me. Thanks for your help

  • By Midwife @Tommys on 7 Feb 2017 - 16:39

    Congratulations on your pregnancy!
    The pain you are describing could be caused by your expanding womb and your hormones. It can sometimes feel like a ‘stitch’. You may also feel light period-like discomfort at the beginning of a pregnancy. These symptoms may be nothing to worry about. However, if you are having persistent abdominal/stomach pain, it should be checked by a doctor or midwife immediately.

  • By Anonymous (not verified) on 5 Feb 2017 - 07:43

    hi,can you kindly calculate my due date my first date of the last period was on 14th november 2016

  • By Midwife @Tommys on 6 Feb 2017 - 10:20

    Using our pregnancy calculator (- see below on our webpage), presuming you have a regular 28 day cycle with a last menstrual period date of 14th Nov 2016 - you would be due on the 21st August 2017.

  • By Anonymous (not verified) on 2 Feb 2017 - 15:20

    Hi. Am 5weeks and 2 days pregnant. But I know I saw my period in December 2016 but can't remember the date. But I had sex twice in this same month 23rd and 30th respectively. Pls can u calculate and tell me which of this dates I took in. Reply

  • By Midwife @Tommys on 2 Feb 2017 - 16:12

    Hi, If you are 5 weeks plus 2 days today then conception would be around 9th January (plus or minus 3-4 days either side).
    For a 28 day cycle that would make your last period around 26th December. Hope that helps

  • By Anonymous (not verified) on 31 Jan 2017 - 03:33

    What causes bleeding at 8 weeks of pregnancy or do having sex during pregnancy causes bleeding.

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