Your Essential Pregnancy Guide: First Trimester (+ Animation)

Parenthood is an adventure. Like all adventures, it needs good planning. So, whether you’re already pregnant, actively trying, or just want to know a little bit more, our first trimester pregnancy guide has got you covered.

We’ll give you an overview of the first trimester, a weekly look at what’s happening to you and baby, plus things you need to do and things to look out for.

In a hurry? Watch the animation below or jump to the section you need:

Overview of the first trimester
Weeks 1-4
Weeks 5-8
Weeks 9-10
Weeks 11-13
Things to do during this trimester
When to call for medical help

Then when you’re ready, we also have second and third trimester guides too. 

Ready? Let’s do this mama.

Overview of the first trimester

Welcome to the first trimester – the first 3 months of your pregnancy journey from week 1 through to the end of week 13. The first trimester begins before you’re even pregnant. The first week of your pregnancy starts with the first day of your last period and includes conception, which usually happens 14 days after your period starting.

You probably won’t look pregnant during your first trimester (you can thank your abs for that), but you’re probably feeling it. In the first few weeks after conception, your hormone levels change massively as your uterus starts to support the growth of the placenta and your baby.

Thanks to this hormone surge, you may start to feel pregnant – think overwhelming tiredness, tender breasts, a metallic taste in your mouth and even the need to pee often (yep, that can kick in already).

There’s also morning sickness which can strike at any time of the day and causes you to feel sick or throw up. Morning sickness is usually worse during the first trimester.

Other things you might experience are:

• No periods or lighter bleeding.
• Breast and nipple changes.
• Bloating, cramps and backache.
• More saliva in your mouth than usual.
• Feeling dizzy or fainting.
• Headaches.
• Constipation and wind.
• No interest in sex or wanting to have sex more often.

It’s not just physical changes. Mentally, the first trimester is a good time to prepare for the realities of pregnancy and the changes it’ll bring.

Whats happening to your baby during the first trimester?

During the first trimester, your baby is changing a lot. It begins as a single fertilised cell and changes into an embryo. This embryo grows rapidly. In a few short weeks, the heart and nervous system begin to form, and limb buds appear.

By the end of the first trimester, baby is moving around (although you won’t be able to feel it yet), the circulation and kidneys are working, and they’re sucking and swallowing. They’re receiving oxygen, blood and nutrients to help them grow from the placenta, which is attached to your baby by the umbilical cord.

Weeks 1 to 4

What’s happening to you?

In week 1, you’re not actually pregnant yet because the first week of your pregnancy is measured from the start of your last period, not from the day you conceive.

By week 4, you should be able to take a pregnancy test and get a positive result. If you’re only just pregnant, your levels of the pregnancy hormone HGC will be quite low so try taking the test first thing in the morning.

What’s happening to your baby?

By week 4, your baby is doubling their size every 12 hours!

Weeks 5 to 8

What’s happening to you?

You can try another pregnancy test in week 5 if you didn’t get a positive result in week 4.

By this time, you might be feeling the effects of morning sickness (we have a morning sickness survival guide if you need it). If so, eat regularly and well and get others to cook if smells make you feel sick. Aim to drink around 2l of clear fluids a day, like water or herbal tea – anything with ginger in will help with the sickness. Plus, as your body’s progesterone levels are higher than normal, the muscles in your intestinal tract are relaxing. By staying well hydrated, you’ll avoid becoming constipated.

During these weeks, your hormones will be going wild and your body will be busy growing things like blood vessels to support your pregnancy. You can blame these hormones for how you might be feeling right now – nauseous, exhausted, needing to pee a lot, tingly breasts, and emotionally a bit all over the place. This is all totally normal – hang in there!

What’s happening to your baby?

By week 5, your baby is the size of an apple seed, their heart is forming and their neural tube (where their brain and spinal cord form) is developing.

By 6 weeks, they’re the size of a pea, their arm and leg buds are developing, and all their vital organs have formed.

By week 7, they’re about 8mm long – the size of a bean. Their muscles, bones and brains are growing, plus their ears, eyes, arms and legs, and their heart is beginning to beat. Baby will start to move although you won’t feel this yet.

By 8 weeks, they’re 2cm long. Their fingers and toes have formed and their skin in paper-thin.

Weeks 9 and 10

What’s happening to you?

Your body is still busy pumping out those pregnancy hormones. These may still be making you feel nauseous, headachy, dizzy and exhausted and giving you tender breasts. You may also be finding it hard to sleep and when you do drop off, you might be having really vivid dreams.

Sound like you? These symptoms will probably hang around for a few more weeks before your body gets used to all the hormones.

What’s happening to your baby?

By 9 weeks your baby is about 2.5cm long. Their face is slowing forming and they have eyelids, a mouth and a tongue. Hands and feet, with ridges where the fingers and toes will be, are beginning to grow and their organs are starting to work.

By week 10, your baby is about 3.5cm, weighs around 9g and their genitals are developing.

Weeks 11 to 13

What’s happening to you?

If this is your first time being pregnant, you probably won’t look pregnant by this stage. That’s because baby’s growth is usually still contained within your pelvic area and held in by your abdominal muscles. You may be aware that your abdomen feels a little fuller than normal but everyone else probably won’t notice yet (with the exception of eagle-eyed soon-to-be grandparents perhaps).

Around this time, you may start to feel some pressure, pain or stretching sensations which are probably due to the ligaments and muscles around your growing uterus stretching. These feelings are normal and aren’t a sign that anything’s wrong. But if you’re worried, talk to your midwife or doctor.

What’s happening to your baby?

By 12 weeks your baby is fully formed and about as long as your thumb. They have all their organs, muscles, limbs and bones and can kick and move.

By the end of week 13, your baby is about 7.5cm long. They can swallow, and their fingerprints have formed.

Things to do in the first trimester

Before you start shopping for baby, there are a few things you need to do first.

Find your lead maternity carer (LMC)

Your LMC is an important person during your pregnancy – they should be your trusted adviser, support person and all-round cheerleader. They’ll guide you through your pregnancy, birth and the first 4-6 weeks of parenthood.

Most LMCs are registered midwives but you can also choose a doctor who provides maternity care or an obstetrician (a doctor who specialises in pregnancy and childbirth).

To find your LMC, you can:

• Ask your doctor for recommendations, especially if you have your pregnancy confirmed by them.
• Ring the Mum2Be helpline – 0800 MUM 2 BE (0800 686 223).
• Visit findyourmidwife
• Ask friends and family who they used and if they’d recommend them.
• Google obstetricians in your area.

You’ll need to tell them your due date to see if they’re available to help. Don’t know it? There’s a due date calculator on the Find your Midwife website.

How to choose your LMC

It’s important to feel comfortable and happy with your LMC – you’ll be going through a very personal and intimate journey with them. Here are some questions you can ask to help you choose the right LMC for you.

Get a blood test and screening

When you first see your LMC (or when you go to the doctor to get your pregnancy confirmed), you’ll be offered a blood test. This test checks multiple things, like whether there are any antibodies that may be harmful to your baby, your iron levels, and if you have diabetes. Find out more about this blood test.

There are other optional tests too, like screening for Down syndrome.

Swot up on birth and baby

Antenatal classes are a great way to learn about what to expect during labour and birth, and how to care for your baby. Plus, you’ll probably meet lots of expectant parents who’ll be invaluable support in your first few months of parenthood.

Ask your LMC about classes in your area and get signed up for a few months’ time.

Take advantage of parental leave

You’re can get up to 10 days unpaid special leave while you’re pregnant. You can use these days for appointments, scans and even antenatal classes and you don’t have to take them as full days.

To take advantage of this, simply let your employer know when you’re planning to use your special leave.

Share the news

It’s a sad reality that 1 in 5 pregnancies end in miscarriage before week 12 so try to hang on until the 12-week mark before sharing your happy news.

When to call for help in the first trimester

By now you probably know that you may not always feel your best during the first trimester, whether you’re battling morning sickness or dealing with extreme tiredness – hopefully you’re breezing through it though, like the glowing Hollywood goddess you are.

Although most of the things you’ll experience are pretty common and normal, some symptoms aren’t.

If you experience any of the below, call your doctor or LMC straightaway:

• Severe abdominal pain or cramps.
• Severe nausea or vomiting.
• Bleeding.
• Severe dizziness.
• Pain or burning during urination.

By the end of week 13, congratulations – you’ve reached the end of the first trimester! Go ahead and see what’s in store for your second trimester.