Pregnancy Week by Week: Your Complete 2026 Timeline & Baby Development Guide

Whether you've just seen that positive test or you're deep into the third trimester, knowing what's happening week by week makes the whole experience feel a little less daunting — and a whole lot more magical. This guide walks you through every stage of your pregnancy timeline, from the very first weeks right through to your due date, covering baby development milestones, common symptoms, and practical tips along the way.

A note on this guide: Pregnancy is measured from the first day of your last menstrual period (LMP), not from the moment of conception. This means the "40 weeks" of pregnancy actually includes around two weeks before you even ovulated.

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The Three Trimesters at a Glance

A typical pregnancy lasts around 40 weeks and is divided into three trimesters:

• First Trimester: Weeks 1–12
• Second Trimester: Weeks 13–27
• Third Trimester: Weeks 28–40

Each trimester brings distinct changes for both you and your baby. Let's look at them week by week.

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First Trimester: Weeks 1–12

What's Happening Overall

The first trimester is arguably the most transformative period of your entire pregnancy. Your body is working overtime to build a baby from scratch, and while there may not be much to see on the outside, an enormous amount is happening within.

During this trimester, your baby grows faster than at any other time. By week 5, all the building blocks for your baby's vital organs are in place, and by week 12, your baby is starting to look more like a tiny human — they even have their own unique fingerprints.

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📅 Weeks 1–4: The Very Beginning

Baby development: Technically, weeks 1 and 2 are before conception — your body is preparing to ovulate. By week 3, fertilisation has taken place in the fallopian tube. The fertilised egg (now called a zygote) begins dividing rapidly as it travels toward the uterus. The fertilised egg then implants into the lining of your womb, where it carries on growing. These layers of cells become an embryo. The amniotic sac begins to form to cushion and protect the embryo, and the placenta starts developing to supply your baby with nourishment.

By the end of week 4, your baby is smaller than a grain of rice — but everything is already in motion.

Common symptoms:

• Missed period — the earliest and most reliable sign of pregnancy
• Light spotting (implantation bleeding)
• Breast tenderness and tingling
• Fatigue
• Mild nausea may begin to appear

Tips for Weeks 1–4:

• Take a folic acid supplement (400mcg daily) if you haven't already — the NHS recommends this from the moment you start trying to conceive through to 12 weeks
• Book a GP appointment to confirm your pregnancy and get a midwife referral
• Avoid alcohol, smoking, and limit caffeine

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📅 Weeks 5–8: The Foundations Are Laid

Baby development: Your baby's facial features begin to form, including the eyes and nose. The heart begins to beat — in fact, a heartbeat can often be detected by around week 6 on an ultrasound. Tiny buds appear that will become your baby's arms and legs. The brain, spinal cord, and nervous system are all forming rapidly. By the end of week 8, your baby is about the size of a kidney bean and is now technically referred to as a foetus.

Common symptoms:

• Morning sickness — though it can strike at any time of day or night, symptoms usually start between weeks 4 and 6
• Extreme tiredness
• Sore, tender breasts
• Frequent urination
• Food aversions and heightened sense of smell
• Bloating

Tips for Weeks 5–8:

• Eat small, regular meals to help manage nausea
• Stay hydrated — sipping cold water or ginger tea can help
• Rest as much as you can; fatigue at this stage is completely normal
• If nausea is severe and you can't keep anything down, speak to your GP — you may have hyperemesis gravidarum, which can be treated

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📅 Weeks 9–12: Hello, Little Foetus

Baby development: This is a period of rapid growth and refinement. Fingers and toes are now fully separated, and fingernails and toenails begin to form. Your baby's bones are beginning to harden. The external ears begin to develop, and the digestive system starts to take shape. By week 12, your baby's bones, muscles, and all the major organs of the body have formed. Their head still makes up roughly half of their total size, but it won't for much longer.

Common symptoms:

• Nausea often peaks around weeks 8–10 and may begin to ease
• Growing a bump — though for many first-time parents, it's barely visible yet
• Headaches
• Heightened emotions
• Constipation

Key milestone: Your dating scan (also called the 12-week scan) typically happens between weeks 10 and 14. This confirms your due date and checks your baby's development. You'll also be offered screening for chromosomal conditions at this scan.

Your first midwife appointment (the "booking appointment") usually takes place between weeks 8 and 10, where your midwife will take your medical history, arrange blood tests, and discuss your care plan.

Tips for Weeks 9–12:

• Start thinking about who you want as your birth partner and discuss it early
• Look into antenatal classes — popular ones book up fast
• Try not to announce your pregnancy at work until after your 12-week scan if you'd prefer to wait

💡 BumpSync Tip: Use BumpSync's pregnancy timeline feature to track exactly where you are week by week, log how you're feeling, and share milestones with your partner in real time. Try BumpSync Free

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Second Trimester: Weeks 13–27

What's Happening Overall

Often called the "honeymoon period" of pregnancy, the second trimester is when many early symptoms ease and you start to show and feel your baby move. Energy levels often return, the risk of miscarriage drops significantly, and many couples feel ready to share the news more widely.

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📅 Weeks 13–16: Growing Fast

Baby development: By week 13, bones are beginning to harden in your baby's skeleton, especially in the skull and the long bones of the arms and legs. The skin is still thin and transparent but will gradually thicken. By week 14, your baby's neck is more defined and red blood cells are forming in the spleen. Baby's sex may become clearer during this period. By week 16, limb movements are becoming more coordinated — something you may even be able to see on an ultrasound.

Common symptoms:

• Reduced nausea for many (though not all)
• Baby bump becoming more visible
• Increased appetite
• Some round ligament pain (stretching sensation in the lower abdomen)
• Skin changes — some people notice a "pregnancy glow", others experience breakouts

Tips for Weeks 13–16:

• This is a great time to start thinking about your nursery — planning ahead reduces stress later on. Browse nursery furniture on BumpSync to start building your wishlist
• Ensure you're getting enough iron and calcium in your diet
• Start gentle pregnancy-safe exercise if you haven't already

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📅 Weeks 17–22: Hello, Baby Kicks!

Baby development: This is one of the most exciting periods for many expectant parents. Around week 18, your baby's ears are forming and they may begin to hear sounds. By week 20, your baby is completely covered in a fine, downy hair called lanugo. The sucking reflex is also developing. Around halfway through your pregnancy — week 20 — you may be able to feel your baby's movements for the first time. This is called quickening and often feels like gentle flutters or bubbles. This typically happens between weeks 16 and 22 for first-time parents.

Common symptoms:

• Feeling baby move (one of the most memorable moments of pregnancy!)
• Back pain as your centre of gravity shifts
• Heartburn and indigestion
• Leg cramps
• Swollen feet and ankles

Key milestone: Your 20-week anomaly scan happens around this time. This detailed ultrasound checks your baby's physical development from head to toe, including the brain, heart, spine, and limbs. If you wish to find out, the sonographer can often determine the baby's sex at this scan.

Tips for Weeks 17–22:

• Start sleeping on your side (left is ideal) rather than your back
• Wear comfortable, supportive footwear
• Consider a pregnancy pillow for better sleep — check out pregnancy pillows on BumpSync

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📅 Weeks 23–27: Viable and Thriving

Baby development: A critical milestone arrives around week 24: your baby's lungs begin producing surfactant, which is vital for breathing after birth. At this stage, your baby is considered viable and could survive with medical support if born early. Your baby's brain is growing and developing quickly. They now have eyelashes and can open and close their eyes. By week 27, your baby is doing lots of kicking and stretching and weighs around 900g.

Common symptoms:

• Braxton Hicks contractions (practice contractions — painless tightenings)
• Stretch marks may appear
• Increased back and pelvic discomfort
• Shortness of breath as your uterus grows
• More frequent baby movements

Tips for Weeks 23–27:

• Stay hydrated and keep active with low-impact exercise like swimming or walking
• Start researching pushchairs and car seats — these are the big-ticket items that take time to decide on
• Consider a hypnobirthing or antenatal course if you haven't already enrolled

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Third Trimester: Weeks 28–40

What's Happening Overall

You're in the home straight! The third trimester is all about your baby putting on weight and fine-tuning their systems ready for birth. You'll have more midwife appointments during this period, and it's the ideal time to get your nursery, hospital bag, and baby kit sorted.

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📅 Weeks 28–32: The Chubby Baby Phase

Baby development: Your baby is gaining weight rapidly — in the last few months of pregnancy, your baby gains roughly half of their birthweight. The brain is growing quickly and developing the ability to help regulate body temperature. Your baby's skin is becoming less see-through as fat layers build up. They're doing lots of kicking and stretching, and you should feel regular movements every day.

Common symptoms:

• Heartburn and reflux (worsens as baby grows)
• Difficulty sleeping
• Increased Braxton Hicks
• Shortness of breath
• Pelvic girdle pain (PGP) for some

Key milestone: Your 28-week midwife appointment includes blood tests (including checking for anaemia and gestational diabetes if not done earlier). You'll also be offered anti-D injections if you're Rhesus negative.

Tips for Weeks 28–32:

• Pack your hospital bag (or at least start a list!) — babies have been known to arrive early
• Research your birth preferences
• Start looking into travel systems and car seats — these need to be fitted correctly before you bring baby home

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📅 Weeks 33–36: Getting Ready

Baby development: Your baby is continuing to gain weight and the lanugo (fine body hair) begins to disappear. They may now have a good amount of hair on their head. By week 35, the brain is still developing significantly — a baby's brain at 35 weeks weighs only around two-thirds of what it will weigh at 39 to 40 weeks. Your baby is also getting into position for birth, and for most, this means head-down.

Common symptoms:

• Difficulty finding a comfortable sleeping position
• Frequent toilet trips as baby presses on your bladder
• Pelvic pressure
• Swelling in hands, feet, and ankles
• Nesting instinct kicks in for many

Tips for Weeks 33–36:

• Finalise your birth plan and share it with your midwife
• Ensure your car seat is installed and tested
• Install your baby monitor and get your nursery fully set up

💡 BumpSync Tip: Use BumpSync's baby prep checklist to make sure you've ticked off everything before baby arrives — from the nursery to feeding essentials. Explore the full prep range on BumpSync and start adding items to your list.

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📅 Weeks 37–40: The Grand Finale

Baby development: Your baby is now considered full term from week 39. Reflexes are becoming more coordinated — your baby can respond to sounds, blink, and grasp. They may move less as space becomes more limited, but you should still feel regular movements. Your baby is getting into position for birth, with the head moving down near the birth canal. By the end of week 40, your baby is around 18–20 inches long and may weigh 7lbs or more — though every baby is different.

Common symptoms:

• Lightening (baby dropping lower into the pelvis)
• Increased pelvic pressure and backache
• More frequent Braxton Hicks
• Possible loss of the mucus plug (show)
• Nesting at full intensity!
• Colostrum leaking from the nipples

Tips for Weeks 37–40:

• Know the signs of labour: regular contractions that get stronger, closer, and longer; waters breaking; or a show
• Keep your phone charged and hospital bag by the door
• Rest as much as you can — labour is hard work
• If your pregnancy is healthy, it's best to wait for labour to begin naturally — births scheduled before 39 weeks should only be for medical reasons

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Tracking Your Pregnancy Week by Week with BumpSync

Keeping track of everything across 40 weeks can feel overwhelming — especially when you're juggling work, appointments, and the emotional rollercoaster that comes with expecting a baby. That's where BumpSync comes in.

BumpSync's pregnancy timeline feature lets both you and your partner follow along week by week, tracking baby's growth, logging symptoms, and ticking off key milestones together. It's completely free to use and designed specifically for couples — because pregnancy is a two-person journey.

Beyond tracking, BumpSync's prep features help you build your baby kit without the overwhelm. From nursery furniture to feeding essentials, every category is organised so you can browse, compare, and add products to your list at your own pace.

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Frequently Asked Questions

When does each trimester start and end?

The first trimester runs from week 1 to the end of week 12. The second trimester is from week 13 to the end of week 27. The third trimester begins at week 28 and runs through to week 40 (or whenever your baby arrives).

How is my due date calculated?

Your estimated due date (EDD) is calculated by counting 40 weeks from the first day of your last menstrual period (LMP). Your dating scan at around 12 weeks will confirm or slightly adjust this date based on your baby's measurements.

When will I feel my baby move for the first time?

Most first-time parents feel their baby move — known as "quickening" — between weeks 16 and 22. It often feels like gentle flutters, bubbles, or a faint tapping sensation. If you've been pregnant before, you may notice it earlier.

When should I tell people I'm pregnant?

This is entirely personal. Many couples wait until after the 12-week scan, when the risk of miscarriage drops considerably. Others choose to tell close friends and family earlier for support. There's no right or wrong answer.

What symptoms should I never ignore during pregnancy?

Always contact your midwife or maternity unit immediately if you experience heavy bleeding, severe abdominal pain, a sudden reduction in baby's movements (after 24 weeks), severe headaches with visual disturbances, or sudden swelling of the face, hands, or feet. Never wait for your next appointment if something feels wrong.

When should I start buying baby things?

Many couples feel comfortable starting their baby prep after the 12-week scan. The bigger purchases — like a travel system, nursery furniture, and car seat — often take weeks to research, order, and deliver, so starting at around 16–20 weeks gives you a comfortable buffer.

Is it safe to exercise during pregnancy?

Yes, for most people, exercise is safe and beneficial during pregnancy. Low-impact activities like walking, swimming, and pregnancy yoga are excellent choices. Always check with your midwife or GP before starting a new exercise regime, particularly if you have any complications.

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Ready to Track Your Pregnancy Journey Together?

Your pregnancy week by week is so much more than a countdown — it's the story of how your family began. BumpSync helps you and your partner stay in sync every step of the way, from tracking weekly milestones to building your complete baby prep checklist.

It's completely free. No subscriptions, no paywalls — just everything you need in one place.

👉 Try BumpSync Free

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Always consult your midwife or GP if you have concerns about your pregnancy, symptoms, or your baby's development. This article is for informational purposes only and does not constitute medical advice.