WhatHappens in Pregnancy?

​Pregnancy is a pretty extraordinary thing. Over roughly nine months, your body grows an entirely new human being while simultaneously adapting your heart, lungs, circulation, digestive system, hormones, muscles and pretty much everything else. And somehow you’re still expected to remember where you put your keys.

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This guide gives you an overview of what happens during pregnancy, from those very early weeks through to the final stretch before birth.

Every pregnancy is different, so think of this as a map rather than a timetable. You might sail through one trimester and crawl through another. You might feel every symptom in the book, or surprisingly few. Neither tells you anything about how well your pregnancy is progressing.

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First things first: How Long is Pregnancy?

 

Pregnancy is usually described as lasting 40 weeks, although babies don't generally arrive neatly on their due date. Your pregnancy is dated from the first day of your last menstrual period, rather than from the day conception actually happened. This means that when you are described as being "4 weeks pregnant", conception may only have happened around two weeks earlier.

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A pregnancy normally lasts somewhere between 37 and 42 weeks, so your estimated due date is exactly that: an estimate. Your dating scan can give you a more accurate estimate of how far along you are. 

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The Three Trimesters

 

Pregnancy is divided into three trimesters.

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First trimester: approximately weeks 1–12

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This is the beginning of some very big changes. Your baby goes from a tiny collection of cells to an embryo with developing organs, limbs and a beating heart. Meanwhile, your body is responding to a huge shift in hormones.

 

You might notice:

• tiredness

• nausea or vomiting

• sore or larger breasts

• needing to wee more often

• constipation or bloating

• changes in taste and smell

• food cravings or sudden food aversions

• headaches

• mood changes

• increased vaginal discharge

• feeling surprisingly emotional about absolutely everything

 

Or you might feel relatively normal. Both can happen. Pregnancy symptoms often begin around 4–6 weeks, but everyone's experience is different.

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What's happening to your baby?

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During the first trimester, development is happening incredibly quickly. The embryo develops the foundations of the brain, spinal cord, heart and other organs. The placenta develops too, eventually becoming the main route for oxygen and nutrients to reach your baby and for waste products to be removed. By the end of the first trimester, your baby has recognisable human features and is moving, although you won't usually be able to feel those movements yet. 

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Second trimester: approximately weeks 13–27

 

For many people, the second trimester brings a welcome change. The exhaustion and nausea of early pregnancy may ease, and you may start to feel more like yourself again.

 

You may also start to:

• develop a noticeable bump

• feel your baby move

• experience round ligament or other aches and pains

• notice changes to your skin and hair

• experience heartburn or indigestion

• become more aware of your changing body

• feel hungrier

• experience back or pelvic discomfort

 

Your uterus is growing rapidly and your body is adapting to accommodate your increasingly wriggly tenant.

 

What's happening to your baby?

 

Your baby's growth and development continue at a remarkable pace. They develop more mature organs and body systems, begin to develop more fat, and become increasingly active. At some point between around 16 and 24 weeks, you will usually start to feel your baby's movements. There is no magic number of kicks that every baby should produce. What's important is getting to know your baby's usual pattern of movement and contacting your maternity team if you notice a change. The second trimester is also when many people have their 20-week screening scan, which looks at your baby's physical development.

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Third trimester: approximately weeks 28–40+

 

Welcome to the final stretch. Your baby is continuing to grow and mature, while your body increasingly has to accommodate a rather large human being taking up residence in your abdomen.

 

You might notice:

• increasing tiredness

• breathlessness

• heartburn

• backache

• pelvic discomfort

• swollen ankles or feet

• difficulty getting comfortable in bed

• needing to wee even more frequently

• Braxton Hicks contractions

• changes in your baby's position and movements

• a general feeling that there is now quite a lot of baby

 

Your body is also preparing for birth. Your cervix will eventually soften and change, your uterus is becoming increasingly responsive to oxytocin, and your baby may move further down into your pelvis. But none of this gives us a reliable countdown clock. A baby being head down at 36 weeks does not mean labour is imminent, and having lots of Braxton Hicks does not necessarily mean you're about to give birth. Babies, frustratingly, do not come with an arrival tracker.

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What happens to your body during pregnancy?

 

Pregnancy isn't simply about your bump getting bigger. Your whole body adapts.

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Your heart and circulation

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Your blood volume increases during pregnancy so that your body can supply both you and your baby. This is one reason you may feel warmer, sweat more easily or occasionally feel dizzy.

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Your digestive system

 

Pregnancy hormones can slow down your digestive system. This can contribute to constipation, bloating and heartburn. Your growing uterus can also put increasing pressure on your digestive organs. So if you've suddenly become very familiar with your local antacid aisle, you're not alone.

 

Your muscles, joints and ligaments

 

As your body changes shape, your centre of gravity changes too. Hormonal and physical changes can contribute to aches and pains, including back pain and pelvic girdle pain. This is one reason movement during pregnancy is so useful. You don't need to train like you're preparing for the Olympics. Walking, swimming, pregnancy yoga and other appropriate forms of movement can all be valuable. The NHS recommends aiming for around 150 minutes of moderate activity across the week, where appropriate, but this can be built up gradually and adapted to your individual circumstances.

 

Your pelvic floor

 

Your pelvic floor muscles support your pelvic organs and are involved in bladder and bowel control, sexual function and birth. Pregnancy places additional load on these muscles, so learning how to both strengthen and relax your pelvic floor is useful preparation for pregnancy, birth and recovery afterwards.

 

Your skin and breasts

 

Your breasts begin preparing for feeding long before your baby arrives. You may notice breast tenderness, growth and changes to your nipples. Your skin may also change. Some people develop stretch marks, darker nipples, pigmentation or the linea nigra, a darker line running down the abdomen. These changes are usually part of the normal physical changes of pregnancy.

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And what about your brain?

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Pregnancy isn't only a physical transformation. It can be a huge emotional and psychological transition.

 

You may feel:

• excited

• nervous

• overwhelmed

• protective

• joyful

• uncertain

• frightened

• impatient

• completely in love with a baby you've never met

• or all of the above before lunchtime

 

There is no single "correct" way to feel about pregnancy. You are also beginning the transition into parenthood, which can bring up questions about identity, relationships, your own childhood, your expectations of birth and what life will look like afterwards. And if you are feeling anxious, low or overwhelmed, please don't wait until things become unbearable before mentioning it. Your midwife, GP or maternity team can help.

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What happens at your pregnancy appointments?

 

Your antenatal appointments are not just about checking whether your bump is growing. They are opportunities to monitor your health, check your baby's wellbeing, discuss screening and tests, answer questions and talk about your choices. You'll usually have appointments with your midwife and may also see other healthcare professionals depending on your individual circumstances.

 

Appointments commonly include things such as:

• checking your blood pressure

• testing your urine

• discussing your wellbeing

• measuring your bump later in pregnancy

• discussing your baby's movements

• offering screening tests

• discussing your birth preferences

• talking about your options as pregnancy progresses

 

The exact schedule can vary depending on whether this is your first baby and whether you or your baby need additional care. You don't have to save all your questions for your next appointment. If you're worried about your health or your baby's health, you can contact your maternity team at any point during pregnancy.

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What should you do during pregnancy?

 

There is a lot of advice out there. Some of it is useful. Some of it is contradictory. Some of it will make you wonder how previous generations ever survived. The basics are actually fairly simple.

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Look after your physical health

 

Eat a varied, balanced diet, stay hydrated and keep your body moving in ways that feel appropriate for you. You don't need to "eat for two". In fact, you don't need additional calories during the first and second trimesters, and only need a modest increase in the third trimester. 

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Keep moving

 

Pregnancy is not an illness. For most people with an uncomplicated pregnancy, staying active is beneficial and safe. Walking, swimming, pregnancy yoga, strength work and other appropriate activities can all form part of a healthy pregnancy. Your body may need you to modify how you move as pregnancy progresses.

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Learn what's happening

 

Understanding pregnancy, birth and your options can make the whole experience feel considerably less mysterious. You don't need to become an obstetrician. You just need enough information to ask good questions and make decisions that feel right for you.

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Look after your mental wellbeing

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Your mental health matters just as much as your physical health. Make space for rest, connection and things that help you feel grounded. And if you're struggling, tell someone. You deserve support during pregnancy, not just once the baby arrives.

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When should you seek help?

 

Most pregnancy symptoms are completely normal, but some need medical attention. Contact your maternity team if you are worried about your health or your baby's health. In particular, seek advice promptly if you experience symptoms such as vaginal bleeding, severe or persistent abdominal pain, severe headache or visual disturbances, significant swelling, fluid leaking from the vagina, feeling very unwell, or a change in your baby's usual movements. You don't need to be certain that something is wrong before asking for help. If your instincts are telling you that something isn't right, it's okay to get checked.

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The most important thing to remember

There is no such thing as a "perfect" pregnancy. You may love being pregnant. You may hate it. You may feel completely amazed by your body. You may occasionally wonder whether your body has been replaced by a tired, hormonal alien. You may experience a mixture of all of these.

 

Pregnancy is a process of constant change. Your body is adapting, your baby is developing and you're gradually preparing for one of the biggest transitions of your life. You don't need to know everything at once. Take it one stage at a time. And when you want to understand what comes next, that's exactly what the rest of The Relaxed Mama Library is here for.

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Explore Next

 

🌱 Common Pregnancy Symptoms
A guide to the symptoms you might experience during pregnancy, what's usually normal and when it's worth getting checked.

 

📅 Due Dates & Gestation
What your estimated due date actually means, how pregnancy is dated and why babies don't follow calendars.

 

🩺 Pregnancy Appointments
What happens at your antenatal appointments and how to get more out of them.

 

🔬 Tests & Screening in Pregnancy
What you're offered, what the tests are looking for and questions you might want to ask before deciding.

 

🧘 Movement in Pregnancy
How movement can support you throughout pregnancy and how to adapt as your body changes.

 

🚩 When to Seek Help
A straightforward guide to symptoms that shouldn't be ignored.

 

🤰 Preparing for Birth
When to start thinking about birth, what you can do to prepare your mind and body, and where to begin.