Stages of pregnancy

Expert reviewer by Dr Evelyn Ferguson, Obstetrician Gynaecologist
Next review due April 2019

During pregnancy, your body goes through a number of important changes. These changes can affect you in various ways at different stages of your pregnancy. 

A pregnancy usually lasts for about 40 weeks. This is calculated from the first day of your last period. The 40 weeks are usually divided into trimesters. Each trimester lasts for 12 to 13 weeks, or around three months. Your first trimester is week 0 to 13 (month 0 to three). Your second trimester is week 14 to 27 (month four to six). And your third trimester is week 28 onwards (month seven to nine).

If you have any questions about your pregnancy or your baby’s development, speak to your midwife. It’s a time when you’re bound to have many questions.


Conception refers to the moment you get pregnant. 

An egg is released from one of your ovaries around 14 days before your period begins. This is called ovulation. This usually, but not always, happens in the middle of a 28-day menstrual cycle. However, cycles can vary in length from woman to woman, and so ovulation is sometimes difficult to predict.

After you have sex, your released egg can be fertilised by one of the millions of sperm from your partner in your fallopian tube. Sperm can survive in your body for up to five days, so you don't need to have sex at the exact time of ovulation to get pregnant. However, your chances of conceiving improve if you have sex regularly in the days leading up to ovulation.

Your fertilised egg then travels along your fallopian tube towards your uterus (womb) where it will bury itself into the lining. This process is called implantation. It takes five to eight days for your fertilised egg to implant itself in your uterus. You may notice some light bleeding when your egg implants in your uterus. 

During this time, your egg continues to grow and divide. From implantation until the end of the eighth week of pregnancy, your egg is called an embryo.

Usually, your uterus loses its lining every month when you have your period. When you become pregnant, you stop having periods. Missing a period is one of the early signs of pregnancy.

An image showing the baby and surrounding structures in late pregnancy

Pregnancy tests

You can buy pregnancy tests at pharmacies and supermarkets. Pregnancy tests work by detecting a pregnancy hormone called beta-human chorionic gonadotrophin (hCG) in your urine. Most types of pregnancy tests can detect if you’re pregnant from the first day of your missed period. If the test result is positive, this means you’re pregnant.

How your baby develops in the womb

Click on the image to open the full-size version.

How your baby develops, stages of pregnancy by Bupa UK

First trimester (one to 12 weeks)

Physical effects of pregnancy on you

Your body goes through many hormonal changes in early pregnancy. This can cause a number of physical signs that indicate you’re pregnant.

As well as missing your first period, you may notice that your breasts feel tender. Your nipples and the area around them (the areola) may become darker. You may find you need to go to the toilet more often too, and you can feel very tired during your first trimester.

Morning sickness

In the first trimester, you may feel sick and perhaps also vomit. This is called ‘morning sickness’, but it can happen at any time of the day. It’s still not clear why some women get morning sickness. But it may be because of the high levels of hormones your body produces while you're pregnant. 

If you have morning sickness, it may help if you:

  • eat little and often – you might find blander foods easier to eat
  • eat plain biscuits 20 minutes before getting up in the morning
  • get plenty of rest
  • drink enough fluids
  • stay away from smells and tastes that make you feel sick
  • take a ginger supplement or drink ginger ale or tea
  • try an acupressure wrist band

Morning sickness can make you feel very unwell but it’s unlikely to affect your baby. If you can’t keep any food or fluids down, see your midwife or GP for advice. This is because you may become very dehydrated, which can affect your overall health.

Digestion problems

Pregnancy hormones relax and slow down the muscles of your digestive system and bowels. This can make you constipated. You can help to prevent constipation by eating plenty of fibre-rich foods, such as vegetables, fruit and cereals containing bran. Also make sure you drink enough fluids every day.

As the muscles of your digestive system relax, this can give you heartburn. Fatty or spicy foods, fruit juices and chocolate can make heartburn worse. Try to eat smaller meals more often and raise the pillow end of your bed so you’re sleeping more upright. Your pharmacist or doctor may be able to recommend some heartburn medicines that are safe to take during pregnancy.

Dietary supplements 

It's important to take folic acid, both before you become pregnant (if possible) and until at least week 12 of your pregnancy. Take 400 micrograms (mcg) of folic acid every day. Folic acid is important for the development of your baby’s brain and spinal cord and can prevent serious problems, such as spina bifida.

If you have diabetes or take certain medicines, you may be advised to take a higher dose of folic acid (5mg a day). Ask your GP or midwife which dose you need to take. 

You should also take vitamin D. The Department of Health recommends all pregnant women take a 10mcg vitamin D supplement during pregnancy.

Smoking and alcohol

Smoking can affect your health and cause problems with your labour and delivery. It can also affect your growing baby’s health during and after pregnancy, increasing their chances of developing health conditions such as asthma and colic. Quitting smoking will protect your baby during pregnancy and after they’re born. Your midwife or GP can direct you to sources of support to help you stop smoking.

The Department of Health recommends that you don’t have any alcohol during your pregnancy or if you’re planning a pregnancy. This is because alcohol is linked to a number of developmental problems in babies. Try not to worry if you drank alcohol before you realised you were pregnant – a small amount of alcohol is unlikely to harm your baby.

Your baby

During the first 12 weeks of your pregnancy, your baby will begin life as a tiny ball of cells and develop quickly into an embryo. From the ninth week of pregnancy, your baby is known as a fetus.

In the first weeks after conception, all your baby’s organs, including their heart, lungs, brain and spinal cord, are developing. By week 12, your baby’s eyes are formed but tightly shut, and their ears are still forming. 

The cells that make up your baby’s heart will start making beating movements from very early on. Your baby’s heartbeat can usually be detected during an ultrasound scan around the sixth week of pregnancy.

Your placenta develops from some of the rapidly dividing cells to create a lifeline between you and your baby. It attaches itself to your uterus and is linked to your baby by the umbilical cord. Oxygen, nutrients and hormones from your blood are transferred through the placenta into your baby. In return, waste products from your baby are transferred back into your circulation, so you can get rid of them.

Second trimester (13 to 27 weeks)

Physical effects of pregnancy on you

Your pregnancy will become more visible during your second trimester. Exactly when this happens varies from woman to woman, but most women look pregnant from around the 20th week of pregnancy.

As your abdomen and breasts grow, you may notice stretch marks on your skin. These are harmless and will usually fade after your baby is born. You can try different moisturisers and lotions to prevent stretch marks but none have been proven to work.

Morning sickness usually gets better by the time you're 16 weeks pregnant. You may have backache and pain in your pelvis because pregnancy hormones cause your ligaments and tendons to relax. This can affect your posture as your baby grows.

You may first feel your baby move when you're around 18 to 24 weeks pregnant. This varies between women and may be a few weeks earlier if it's not your first pregnancy. The movements will become much more vigorous and obvious as your baby gets bigger and stronger. If you can’t feel your baby moving, or they’re moving less often, contact your midwife.

Your baby

In your second trimester, your baby's organs continue to grow and mature. Your baby’s kidneys begin to work and pass small amounts of urine. He or she will sleep and wake regularly, and may start to kick and stretch. They may even suck their thumb if their hand reaches their mouth. Your baby grows fingernails, and teeth begin to develop under their gums. 

By 20 weeks, your baby is able to hear and is covered in fine hair called lanugo. If you have a scan at this stage, it's often possible to find out whether your baby is a boy or a girl.

From 24 weeks, your baby has a chance of surviving if they’re born prematurely, though their chances improve with every week they stay inside your womb. Babies born prematurely can have many health problems, including breathing problems, difficulties feeding and a high risk of infections. But major advances in specialist care for premature babies mean many more survive now, even as early as 24 weeks.

Third trimester (28 to 40 weeks)

Physical effects of pregnancy on you

You may find that the extra weight you’re carrying makes you tired, and you might become breathless as your baby grows. Your midwife may check your iron levels to make sure you don’t have anaemia if your tiredness and breathlessness continue. 

You may have trouble finding a comfortable position to sleep in. Your sleep might also be disturbed if you wake to go to the toilet in the night and have backache, cramps or unpleasant dreams.

Braxton-Hicks contractions – practice contractions – can start in your second trimester, but are much more common in your third trimester. These can be mistaken for labour, but don’t cause any pain, although they can be uncomfortable. You usually get only one or two Braxton-Hicks contractions every hour.

Your baby

During your third trimester, your baby gains weight. Their lungs are mature, although they won’t work properly until they are born. Your baby also responds to sound.

Your baby will be developing fat stores and it’s likely that they will turn into a head-down position to prepare for the birth.

Weight gain in pregnancy

You will put on some weight during your pregnancy, but the exact amount varies from woman to woman. Your midwife will weigh you at your first appointment and also measure your height. They will use these measurements to work out your body mass index (BMI). Your midwife may ask you about what and how much you eat and also about your exercise habits. 

Unless you’re very over or underweight, your midwife probably won't weigh you again during your pregnancy. But if you're concerned about your weight gain, talk to your midwife or GP.

The weight you gain during pregnancy doesn’t mean you’re getting fat. This extra weight is made up of:

  • your developing baby, placenta and amniotic fluid
  • the increased blood in your circulation
  • water retention
  • essential fat stores

Frequently asked questions

  • Yes, you can fly during pregnancy, up to a certain point, and as long as your pregnancy hasn’t caused any complications to your health.

    More information

    There’s no evidence that flying is unsafe for you or your baby during pregnancy. But you should speak to your GP or midwife about how it could affect you if you’re thinking of travelling. Some pregnant women experience swollen ankles and nasal congestion during a flight. Flying can make morning sickness worse and cause dehydration. If you’re planning a long-haul flight, your risk of deep vein thrombosis (DVT) may also be higher when you’re pregnant. Make sure you drink enough fluids and flex your ankles to keep your blood circulating. You may also want to wear flight stockings. 

    You should check with your airline before you book the tickets, as airlines have their own guidelines and rules for taking pregnant passengers. If you choose to fly after you're 28 weeks pregnant, your airline may ask for a letter from your GP or midwife. This will need to confirm your due date and that you’re not at an increased risk of complications by flying.

    Most airlines won’t let pregnant women fly from 37 weeks. This is because there’s more chance you will go into labour. You may find it more difficult to get travel insurance after a certain point in your pregnancy too.

  • Yes, but you may need to adapt your usual routine, as some activities may not be suitable when you’re pregnant. 

    More information

    Exercising when you’re pregnant can keep you and your baby healthy, and reduce your risk of complications. You might need to take some precautions when choosing which type of exercise to do though. 

    Swimming is considered to be an ideal form of exercise for pregnant women. This is because it’s gentle on your joints and isn’t affected by your weight gain. Walking is good for your heart, and is another ideal form of exercise for pregnant women, especially as you can take it at your own pace.

    Don’t begin aerobics classes, weightlifting or try out a new sport for the first time in pregnancy.

    Contact sports, high impact sports or racquet sports aren’t suitable when you’re pregnant because of the risk of injury. When you’re pregnant, you shouldn’t scuba-dive either, no matter what your skill level is. This is because your baby can’t be protected against the effects of water pressure, such as decompression sickness. 

    The hormones you produce when you're pregnant can make your joints weaker. Pregnancy can make your recovery from an injury longer than usual or more complicated. It’s a good idea to warm up before you exercise and cool down afterwards.

    If you feel any unusual symptoms during exercise, such as dizziness or pain, it's best to stop and contact your midwife or GP.

  • This means that inside your uterus, your baby's bottom or feet, rather than their head, are pointing downwards.

    More information

    Most babies move their head downwards, towards the neck of the womb, before they’re born. This is the natural position that makes birth more straightforward. A few babies lie with their bottom down at the neck of the womb instead. Most babies turn so they are head down in the last few weeks of pregnancy. By the time babies are ready to be born, only around three in 100 will still be in the breech position.

    When you go to your later antenatal appointments, your midwife will check the position of your baby. If your baby is breech at 36 weeks, you may be referred to an obstetrician (a doctor who specialises in pregnancy and childbirth). 

    Your doctor will discuss a procedure to try to turn your baby so they’re head down before birth. Your obstetrician will place their hands on your abdomen and try to move your baby inside your uterus. They will try to turn your baby – this is called an external cephalic version. An external cephalic version can feel uncomfortable at times – be sure to ask your doctor to stop if it's painful. Your baby’s heartbeat will be monitored before and after any attempt to turn the baby.

    If your baby is still in the breech position after the procedure, your doctor will talk to you about your options for the birth. You may choose to have either a vaginal breech birth or a caesarean delivery. Your doctor will help you to decide on the best option.

  • At first, your baby's movements may feel like 'flutters' in your lower abdomen (tummy). Some women describe the sensation like bubbles popping. Later on, you may feel your baby kick, stretch or roll. This rarely causes discomfort and feeling your baby move is very reassuring that all is well.

    More information

    From around week 18, you may begin to feel slight movements from your baby. If you’ve had a baby before, you may notice movements earlier than this because you recognise the sensation. You’re more likely to notice your baby moving when you’re sitting or lying down quietly.

    As your baby continues to grow and get stronger, you will feel more definite and vigorous kicking and prodding. Some babies are more active than others, but it's important to recognise your own baby’s pattern of activity. If you notice any sudden changes in the pattern of your baby's movements, contact your midwife or hospital obstetric unit to check your baby is well.

About our health information

At Bupa we produce a wealth of free health information for you and your family. We believe that trustworthy information is essential in helping you make better decisions about your health and care. That’s why our content is produced to the highest quality standards. Look out for the quality marks on our pages below. You can find out more about these organisations and their standards on The Information Standard and HON Code websites.

Information standard logo  This website is certified by Health On the Net Foundation. Click to verify.

Learn more about our editorial team and principles >

Related information

    • Common pregnancy complaints and questions. Medscape., reviewed 19 December 2014
    • Gould JE, Overstreet JW, Hanson FW. Assessment of human sperm function after recovery from the female reproductive tract. Biol Reprod 1984; 31:888–94
    • Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation – effects on the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med 1995; 333:1517–21
    • Prenatal development: how your baby grows during pregnancy. The American Congress of Obstetricians and Gynaecologists., reviewed June 2015
    • Conception and prenatal development. The MSD Manuals., reviewed October 2013
    • Gynaecology. Oxford Handbook of General Practice (online). 4th ed. Oxford Medicine Online., published online April 2014
    • Pre-pregnancy counselling. PatientPlus., last checked 28 January 2016
    • Hill MA (2016) Embryology., accessed 18 February 2016
    • Female reproductive endocrinology. The MSD Manuals., reviewed April 2013
    • Physiology of pregnancy. The MSD Manuals., reviewed October 2013
    • Pregnancy. Oxford Handbook of General Practice (online). 4th ed. Oxford Medicine Online., published online April 2014
    • Nausea and vomiting in pregnancy. Clinical Knowledge Summaries., reviewed June 2013
    • Nausea and vomiting in pregnancy. BMJ Best Practice., reviewed 11 May 2015
    • Constipation. The MSD Manuals., reviewed November 2013
    • Dyspepsia – pregnancy associated. Clinical Knowledge Summaries., reviewed December 2012
    • Smoking: stopping in pregnancy and after childbirth. National Institute for Health and Care Excellence (NICE), August 2015.
    • Alcohol Guidelines Review. Report from the Guidelines Development Group to the UK Chief Medical Officers. Department of Health., published January 2016.
    • Premature birth statistics. Tommy’s., accessed April 2016
    • Placenta and placental problems. PatientPlus., last checked 2 July 2015
    • Normal sleep. OPL Sleep Disorders (online). 2nd ed. Oxford Medicine Online., published online October 2013
    • Normal labor and delivery. Medscape., reviewed 2 May 2014
    • Weight management before, during and after pregnancy. National Institute for Health and Care Excellence (NICE), July 2010.
    • Air travel and pregnancy. Royal College of Obstetricians and Gynaecologists., reviewed January 2015
    • Advice for mothers-to-be and new mothers. Pelvic Obstetric and Gynaecological Physiotherapy., published January 2015
    • Breech presentations. PatientPlus., last checked 11 March 2013
    • Breech presentation. Medscape., reviewed 13 January 2015
    • Your baby’s movements in pregnancy. Royal College of Obstetricians and Gynaecologists., reviewed August 2012
  • Reviewed by Alice Rossiter, Specialist Health Editor, Bupa Health Content Team, April 2016
    Expert reviewer Dr Evelyn Ferguson, Obstetrician Gynaecologist
    Next review due April 2019

Has our health information helped you?

We’d love to know what you think about what you’ve just been reading and looking at – we’ll use it to improve our information. If you’d like to give us some feedback, our short survey on the right will take just a few minutes to complete. And if there's a question you want to ask that hasn't been answered here, please submit it to us. Although we can't respond to specific questions directly, we’ll aim to include the answer to it when we next review this topic.