What are the different stages of pregnancy?

Samantha Wild
Clinical Lead for Women's Health and Bupa GP
31 August 2023
Next review due August 2026

Pregnancy usually lasts between 37 and 42 weeks. It’s split into three stages, known as trimesters. Each stage of pregnancy lasts for around 12 to 13 weeks. During this time, your body goes through lots of changes to support your growing baby and prepare for birth.

Here I look at what happens during each trimester, and the changes you might experience week by week.

pregnant person holding the belly

When do you start to feel pregnant?

Pregnancy begins the moment a sperm joins with an egg (known as conception). But you might not start to feel pregnant, or notice symptoms, for a little while.

Missing a period is often the first sign that you might be pregnant, if you usually have regular periods. Most pregnancy tests can detect pregnancy from the first day of your missed period. You can usually buy tests at your local supermarket or pharmacy.

How many weeks pregnant am I?

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. But it’s normal to give birth up to three weeks before, or two weeks after, your due date. And, your initial due date can change based on measurements taken at your ultrasound scan.

What happens during the first trimester? (1 to 12 weeks)

Below are some common symptoms that you might experience during this first stage of pregnancy.

  • Missing your period.
  • Having tender breasts.
  • Needing to pee (urinate) more often than usual.
  • Feeling tired.
  • Feeling sick or being sick. This is often called morning sickness, but it can happen at any time of day.
  • Being constipated. Drinking lots of fluids and getting plenty of fibre can help.

Many of these symptoms will fade as your pregnancy continues. Speak to your GP or midwife if you’re struggling with any of your pregnancy symptoms.

It’s important to try and be as healthy as possible during your pregnancy. You should:

  • stop smoking if you smoke
  • avoid drinking alcohol
  • not eat undercooked meat or unpasteurised dairy products
  • take folic acid (until you’re 12 weeks pregnant) and vitamin D supplements throughout your pregnancy

Speak to your GP and midwife about any lifestyle changes you could make.

How is my baby developing in the first trimester?

Your baby begins life as a tiny ball of cells. Some of the cells become an embryo and some form the placenta.

The placenta attaches to your womb and is linked to your baby by the umbilical cord. Oxygen, nutrients, and hormones from your blood pass through the placenta and umbilical cord into your baby. Your baby’s waste products pass back into your blood, so you can get rid of them.

During these first few weeks, all your baby’s organs and body parts start to form. The cells that create your baby’s heart start making beating movements. Your baby’s heartbeat can be detected during an ultrasound scan around week six of pregnancy. And, by week 12 your baby is starting to look more like a little person.

What happens during the second trimester? (13 to 27 weeks)

In your second trimester your body continues to change.

  • You’ll start to put on weight as your baby grows. This extra weight is made up of your baby, placenta, fluid in your womb, your growing breasts, extra fluid, and fat stores.
  • As your tummy and breasts grow, you may notice stretch marks on your skin. These are harmless and usually fade after your baby is born. Lots of moisturisers and lotions claim to prevent them but there’s little evidence that they work.
  • Morning sickness usually improves between 16 and 20 weeks pregnant.
  • You may get backache, and some people experience pelvic pain and find it harder to walk. Physiotherapy can help manage this.
  • You may first feel your baby move between 16 and 24 weeks pregnant. The movements will get stronger as your baby gets bigger and more active. Make time to notice your baby’s movements and get to know their usual pattern. Contact your midwife or antenatal ward immediately, at any time of day or night, if you notice less movement.

How is my baby developing in the second trimester?

Around this time your baby can hear some sounds. By 20 weeks, their digestive system is working.

Your baby’s skin will be wrinkled and covered with a greasy substance and fine hair called lanugo. They’ll sleep and wake regularly and may start to kick and stretch. Their sucking reflex is developing, and they may even suck their thumb.

You can usually find out the sex of your baby at your 20-week screening scan, if you choose to. This scan is offered when you’re between 18 and 20 weeks pregnant. But, this depends on your local hospital’s policy. Ask the person doing the scan beforehand if you’d like to try and find out.

From 24 weeks your baby has a chance of surviving if they’re born prematurely, but they’d need intensive care for a long time if they were born this early. Their chance of surviving improves the longer they stay inside your womb.

What happens during the third trimester? (28 to 40 weeks)

In your third trimester your baby continues to grow, and your body prepares for birth. Below are some symptoms you might experience at this stage of pregnancy.

  • You might feel tired and breathless as your baby grows. Sometimes, this may be caused by iron-deficiency anaemia. You’ll be offered blood tests to check your iron levels during your pregnancy.
  • You may find it harder to sleep.
  • You might start getting Braxton–Hicks contractions from about 30 weeks. These can be uncomfortable but shouldn’t hurt.
  • Heartburn. Try to eat little and often, stick to bland foods, and avoid eating late at night.
  • Swelling can happen later in pregnancy, in your ankles, feet, legs, hands, or fingers. If this happens suddenly or gets a lot worse, contact your midwife. It can be a sign of pre-eclampsia which can be very dangerous for you and your baby.
  • Varicose veins, when blood doesn’t flow properly through the veins closest to the surface of your skin.
  • You might notice a milky fluid called colostrum leaking from your breasts.
  • You may need to pee more often and might leak some urine when you cough or sneeze. Pelvic floor exercises can help with this.

How is my baby developing in the third trimester?

During the third trimester, your baby puts on weight and stores fat ready for when they’re born. Their skin starts to smooth out and they lose their coat of fine hair (lanugo).

During this time your baby will continue to move a lot. They usually turn into a head-down position by week 36, ready for birth. And, in the last few weeks, they tend to drop lower into your pelvis.

For more information, you can also watch our video below on the stages of pregnancy.

Are you interested in learning more about your health? Discover more about our range of health assessments.

Samantha Wild
Dr Samantha Wild
Clinical Lead for Women's Health and Bupa GP



Lucy Kapoutsos, Health Content Editor at Bupa UK

    • Physiology of pregnancy. The MSD Manuals., last updated September 2022
    • Medical terms explained. Trimester. Royal College of Obstetricians and Gynaecologists., accessed August 2023
    • Medical terms explained. Conception. Royal College of Obstetricians and Gynaecologists., accessed August 2023
    • Common pregnancy complaints and questions. First trimester. Medscape., updated April 2020
    • Am I pregnant? Brook., accessed August 2023
    • Screening in pregnancy: dating scan. Public Health England. Last updated 31 October 2021
    • Common pregnancy complaints and questions. Medscape. Updated 8 April 2020
    • Antenatal care – uncomplicated pregnancy. Scenario: managing common minor ailments. NICE Clinical Knowledge Summaries. Last revised February 2023
    • Antenatal care – uncomplicated pregnancy. NICE Clinical Knowledge Summaries. Last revised February 2023
    • Foods to avoid in pregnancy. Tommy’s. Last reviewed 5 March 2021
    • Placenta complications. Tommy’s. Last reviewed 12 July 2019
    • Everything you need to know about the first trimester (weeks 1 to 12). Tommy’s. Last reviewed 28 June 2018
    • Healthy weight in pregnancy. British Nutrition Foundation. Last reviewed June 2015
    • Striae (stretch marks) Primary Care Dermatology Society. Last updated 19 November 2021
    • Nausea/vomiting in pregnancy. NICE Clinical Knowledge Summaries. Last revised December 2021
    • How can I reduce irritable back pain? Tommy’s. Last reviewed 10 September 2018
    • Pelvic girdle pain and pregnancy. Royal College of Obstetricians and Gynaecologists. Accessed August 2023
    • Your Baby’s Movements – FAQ about baby movement. Kicks Count. Accessed August 2023
    • Reporting reduced fetal movements. Tommy’s. Accessed August 2023
    • Fetal Growth and Development. United Kingdom, Cambridge University Press, 2001
    • Myles' Textbook for Midwives E-Book. United Kingdom, Elsevier Health Sciences, 2014
    • 20-week screening scan. Last updated 4 May 2023
    • 20-week screening scan. NHS. Last reviewed 7 April 2021
    • Premature birth statistics. Tommy’s. Accessed August 2023
    • Common side-effects of pregnancy. Patient. Last updated 24 September 2021
    • Scenario: Antenatal care – uncomplicated pregnancy. NICE Clinical Knowledge Summaries. Last revised February 2023
    • Braxton hicks. Tommy’s. Last reviewed 3 July 2019
    • Dyspepsia – pregnancy associated. Scenario: management. NICE Clinical Knowledge Summaries. Last revised April 2023
    • Swollen hands and feet in pregnancy. Tommy’s. Last reviewed 21 February 2023
    • Pre-eclampsia patient information leaflet. Royal College of Obstetricians and Gynaecologists. Accessed August 2023
    • Varicose veins. NICE Clinical Knowledge Summaries. Last revised February 2020
    • Urinary incontinence in women: what are the causes and contributing factors for urinary incontinence? NICE Clinical Knowledge Summaries. Last revised April 2023
    • Development of organs. Britannica. Accessed August 2023
    • Your baby’s movements in pregnancy – patient information leaflet. Royal College of Obstetricians and Gynaecologists. Last updated February 2019
    • Breech baby at the end of pregnancy. Royal College of Obstetricians and Gynaecologists. Published July 2017

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