Stages of pregnancy

Expert reviewer, Dr Samantha Wild, General Practitioner, Bupa UK
Next review due December 2021

A typical pregnancy normally lasts from 37 to 42 weeks, counting from the first day of your last period. The 40 weeks are divided into trimesters, with each one lasting for three months, or around 12 to 13 weeks.

When you’re pregnant, your body will go through a number of important changes to support your developing baby and get ready for childbirth. Here we outline what you can expect during the different stages of pregnancy.

Getting pregnant

Getting pregnant means a sperm from your partner has joined together with (fertilised) one of your eggs. The moment when this happens is called conception. An egg is released from one of your ovaries every month, usually around 14 days after the start of your last period. This is called ovulation. If you’ve had sex, the egg may be fertilised by sperm from your partner in your fallopian tube. The fertilised egg then travels along your fallopian tube towards your womb (uterus). During this time, the fertilised egg rapidly grows and divides, becoming a ball of cells.

Once it reaches your womb, the ball of cells buries itself into the womb lining. This process is called implantation. It takes around five to eight days for your fertilised egg to travel from your fallopian tube and implant itself in your womb. At this early stage, the baby that starts to grow in your womb is known as an embryo. Usually, your womb sheds its lining every month, causing your period. This is usually around 14 days after ovulation. When you’re pregnant, your womb won’t shed its lining, so you’ll stop having periods. Missing a period is often the first sign that you’re pregnant.

Pregnancy tests

You can buy pregnancy tests at any pharmacy or supermarket. You may also be able to get one free of charge from certain charities, contraceptive and sexual health clinics, and your GP. Pregnancy tests work by detecting a pregnancy hormone called beta-human chorionic gonadotrophin (hCG) in your urine.

Most pregnancy tests can detect if you’re pregnant from the first day of your missed period. Some tests are more sensitive and are able to give you a result even earlier. Pregnancy tests are usually very accurate but a negative result may not be accurate if you do the test very early on. It’s worth repeating a negative test after a few days because during the first few weeks of pregnancy, your level of hCG increases rapidly. By the time your period is about a week late, you can be pretty sure that the result of a pregnancy test is accurate.

How many weeks pregnant am I?

Pregnancy is counted from the first day of your last period. So if you have a 28-day menstrual cycle, you’re said to be four weeks pregnant on the day your next period would have been due. If it’s been a week since your period was due, you’ll be 5 weeks pregnant.

Your doctor or midwife will calculate your due date based on the date you started your last period. Your due date is 40 weeks from this date – although it’s normal to give birth up to three weeks before or two weeks after this date.

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First trimester (one to 12 weeks)

Effects of pregnancy on you

Your body goes through many changes in early pregnancy. The following may be some of the first signs that you’re pregnant.

  • Missing your period – this is often the first sign that you’re pregnant.
  • Your breasts may feel fuller and tender, and your nipples and the area around them (the areola) may become darker.
  • You may find you need to pass urine more often, as your womb gets bigger and starts to press on your bladder.
  • You can feel very tired and drowsy as a result of all the changes happening in your body.
  • You might get pulling pains around the sides of your abdomen, as your womb grows bigger and stretches the ligaments around it.
  • You may feel sick or vomit. This is often called ‘morning sickness’, but it can happen at any time of the day. It’s very common early on in pregnancy. It can help to eat little and often and stick to blander foods. See our Pregnancy problems and complications article for more information.
  • It’s common to get constipation during pregnancy because the passage of food through your digestive system slows down. Make sure you’re drinking enough fluids and including plenty of fibre in your diet. See Pregnancy problems and complications for more tips.

Many of these symptoms will settle down as your pregnancy continues but some things, like constipation, may carry on or get worse.

You may already be following a healthy lifestyle but if you’re not, there are a number of changes you should make when you become pregnant. This is important, so that your pregnancy is as healthy as it can be. These changes include giving up smoking if you smoke, and stopping drinking alcohol if you normally do so. You should also be careful about what you eat, and make sure you take folic acid and vitamin D supplements. Read our information on Planning for pregnancy for more detail.

How your baby develops

Your baby begins life as a rapidly growing, tiny ball of cells that quickly develops into an embryo.

During these first few weeks, all your baby’s organs and important body parts begin to form. Some of the cells develop into the placenta, which creates a lifeline between you and your baby. The placenta attaches itself to your womb and is linked to your baby by the umbilical cord. Oxygen, nutrients and hormones from your blood are transferred through the placenta and umbilical cord into your baby. Waste products from your baby are transferred back into your blood, so you can get rid of them. The cells that start to form your baby’s heart 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.

Second trimester (13 to 27 weeks)

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. Here are some other changes you can expect during your second trimester.

  • You’ll start to put on more weight as your baby grows. The exact amount varies from woman to woman, but it’s usually around 9 to 11.5 kg (20 to 25 pounds) throughout your pregnancy. The extra weight is made up of your developing baby, the placenta, the fluid in your womb, your breasts, and extra fluid and fat stores.
  • As your abdomen and breasts grow, you may notice stretch marks on your skin. These are harmless and usually fade after your baby is born. You can try different moisturisers and lotions to prevent stretch marks but there is little evidence that any of these work.
  • Morning sickness usually gets better by the time you're 16 weeks pregnant.
  • Pregnancy hormones cause your ligaments and tendons to relax, loosening your joints. Combined with the extra weight you’re carrying, this may result in backache. You may also get pain in your pelvis and have some difficulties walking.
  • You may first feel your baby move when you're around 18 to 20 weeks pregnant. It may be a few weeks earlier if it's not your first pregnancy. The movements become much more vigorous and obvious as your baby gets bigger and stronger. For more information , see our FAQ What will it feel like when my baby kicks?

How your baby develops

In your second trimester, your baby's organs continue to grow and mature. Your midwife will be able to hear your baby’s heartbeat with a stethoscope from about 16 to 20 weeks. Your baby’s kidneys begin to work and pass small amounts of urine. Their ears develop and by 16 weeks, your baby can start to hear some sounds.

Your baby’s skin will be wrinkled and covered with a greasy substance, and fine hair called lanugo. 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. Their eyelids will open by the time they’re about six months. By the 20th week of pregnancy, it's usually possible to see on an ultrasound whether your baby is a boy or a girl.

From 24 weeks, your baby starts to have more chance of surviving if they are born prematurely. But they would need intensive care for a long time if they were born this early. Their chances of surviving improve with every week they stay inside your womb.

Third trimester (28 to 40 weeks)

Effects of pregnancy on you

Here are some of the main changes you can expect in your final trimester, as your baby continues to grow and your body prepares for childbirth.

  • The extra weight you’re carrying can make you very tired, and you might become breathless as your baby grows. Sometimes, these problems are caused by anaemia. You should be offered blood tests at your first midwife appointment and again when you’re 28 weeks pregnant, to check for this.
  • You might be finding it hard to sleep, which will also make you tired. It’s common to wake up a lot in the later stages of pregnancy because needing the toilet more often or feeling uncomfortable can disrupt your sleep.
  • You might get Braxton–Hicks contractions – where your womb starts to contract – from about 30 weeks onwards. These may be uncomfortable, but shouldn’t be painful.
  • It's common to get heartburn in pregnancy, and this is more likely to affect you in the third trimester. Try to eat little and often, and stick to bland foods. Avoid eating late at night. You can try an antacid medicine to see if it helps.
  • Many pregnant women suffer with swelling later in pregnancy, especially in their ankles, feet, legs, hands or fingers. If this happens suddenly or gets significantly worse, contact your midwife because it can be a sign of pre-eclampsia (high blood pressure during your pregnancy).
  • It’s also common to develop varicose veins at this stage, as the blood flow around your legs slows down.
  • Your breasts will start to produce a milky fluid called colostrum towards the end of your pregnancy. You might notice that your breasts start to leak some of this fluid.
  • You may find you need to pass urine more often as your baby descends into your pelvis. You may lose some bladder control too, for instance passing urine when you cough or sneeze. This is known as stress incontinence.

How your baby develops

By this point in your pregnancy, most of your baby’s major development is complete. During this trimester, your baby gains weight very quickly and develops fat stores beneath their skin. Their skin starts to smooth out and they lose their coat of fine hair. Their body gradually becomes more in proportion. Their lungs mature but won’t work properly until they’re born.

Your baby usually turns into a head-down position, ready for birth. In the last few weeks, they drop lower into your pelvis.

An image showing the baby and surrounding structures in late pregnancy

Frequently asked questions

  • Yes, you can fly during pregnancy, usually up until you’re 37 weeks pregnant, as long as your pregnancy isn’t causing any complications. It’s important that you check with your airline first because different airlines have different rules and guidelines.

    There’s no evidence that flying is unsafe for you or your baby during pregnancy. But you should speak to your midwife or GP about how it could affect you, as flying might be uncomfortable when you’re pregnant. You may be more likely to get swelling in your legs if you fly. You may also get a blocked nose, which can cause pains in your ears. If you have morning sickness, flying might make it worse. Your risk of developing deep vein thrombosis (DVT) as a result of flying is higher when you’re pregnant.

    If you’re planning a long-haul flight, you might need to take some precautions to prevent DVT. These include having regular drinks throughout your flight, doing some exercises in your seat to keep your blood circulating and wearing compression stockings.

    If you choose to fly after you're 28 weeks pregnant, your airline may ask for a letter from your GP or midwife. This should 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 after they are 37 weeks pregnant. 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.

  • Yes, most types of exercise are perfectly safe when you’re pregnant. In fact, pregnancy can be a good time to start a healthier lifestyle and get more active. However, there are certain sports that are best avoided and some where you may need to take extra care while you’re pregnant. Being active is important to keep yourself fit and healthy while you’re pregnant.

    Some types of exercise, such as swimming and walking, are particularly suited to pregnancy, as they are gentle on your joints. If you’re already used to doing other activities, like running or racquet sports, these can be safe to carry on with during pregnancy. You may just need to adapt what you do as you go through your pregnancy. For instance you may need to jog slowly rather than run, and then switch to walking later in your pregnancy.

    If you haven’t done much exercise before, pregnancy is definitely a good time to start – just build it up slowly. Start with 10-minute bouts of activity, and try to gradually do more. It’s not a good idea to do high-intensity activities like running or racquet sports in pregnancy if you haven’t done them before.

    It’s best to avoid any activities with a high risk of injury when you’re pregnant; these include contact sports, skiing and horse riding. You also should avoid any types of exercise where you need to lie flat on your back, like aerobics, yoga and Pilates. These exercises can often be adapted for pregnant women, so discuss with your instructor what you may be able to do instead.

    If you feel uncomfortable or have any unusual symptoms while you’re exercising, it's best to stop and contact your midwife or GP. Such symptoms include bleeding, dizziness or pain.

    Read our information on Exercising during and after pregnancy for more tips.

  • This means that your baby's bottom or feet are pointing downwards inside your womb, rather than their head. It’s common for babies to be in the breech position early in pregnancy, but most babies move their head downwards before they’re born. This is the usual position for childbirth, and makes birth more straightforward. 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). You may be offered a procedure to manually try to turn your baby so they’re head down before birth. This is called an external cephalic version (ECV). It involves applying gentle, firm pressure to your abdomen to try to move your baby inside your womb. An ECV can feel uncomfortable at times, but your doctor or midwife will stop if it's painful.


    ECV doesn’t always work. If your baby is still in the breech position after the procedure, your doctor will talk to you about your options for the birth. These include having either a vaginal breech birth or a caesarean delivery. Your doctor will explain the risks and benefits involved in each option, and help you to decide which is best for you.

  • Most women first feel their baby moving at around 18 to 20 weeks of pregnancy. At first, your baby's movements may feel like flutters in your lower abdomen (tummy). It’s sometimes called ‘quickening’. Some women describe the sensation like a tickling or feathery feeling. You’re more likely to notice your baby moving when you’re sitting or lying down quietly. Usually, they will be more active in the afternoon and evening.

    As your baby continues to grow, you’ll feel more definite, stronger and regular movements. Your baby should keep making these movements right up until you go into labour. Some babies are more active than others, but it's important to recognise your own baby’s pattern of activity. Your baby’s movements are an important sign of their wellbeing.

    If you’ve been busy, it can sometimes be easy to miss your baby’s movements. If you’re not sure whether you’ve felt your baby move as much normal, take some time to lay down quietly on your left side and focus on your baby’s movements.

    If you’re in any doubt about whether your baby is moving as much as normal, contact your midwife or maternity unit straight away. Your midwife will listen for your baby’s heartbeat and may suggest you have an ultrasound scan to check that your baby is well.

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  • Reviewed by Pippa Coulter, Freelance Health Editor, December 2018
    Expert reviewer, Dr Samantha Wild, General Practitioner, Bupa UK
    Next review due December 2021