Pregnancy week by week: your first trimester

Whether you’re currently in the early stages of pregnancy or planning to conceive, you’ll want to know what to expect in the first trimester. This can be an overwhelming time involving endless cover stories for why you’re not feeling great, and going to a crapload of appointments. But boy oh boy is it incredible. When you think about what’s actually happening inside you (you’re making a brain! And bones! And organs!) you can’t help but be in awe of it all.

This useful guide will walk you through those exciting (sometimes vomit-ey) first trimester weeks. We’ll help you understand what’s going on in your body, what first trimester pregnancy symptoms (week by week) to expect, and what steps you should take to ensure a healthy pregnancy. 

Week 1

Truth be told, you’re not technically ‘pregnant’ yet. In fact, you’ll have your period this week which will feel about as far from pregnancy as you can get – but your obstetrician will retrospectively calculate your due date from the start of this period.

Things to do 

  • Stock up on vitamins – During your pregnancy planning consultations, your doctor will have prescribed a suite of pregnancy supplements including a good prenatal vitamin, folic acid and Vitamin D.
  • Assess your diet – Follow your doctor’s advice on foods to eat when pregnant. First trimester eating habits will change a little, as there are some foods and drinks you should avoid.

Week 2

You’re ovulating this week, and you know what that means? Time to get frisky. You might feel hella horny during ovulation when your estrogen levels spike – your body’s way of saying, “Put a baby in me.”

Ovulation tracking apps can help you work out your exact fertile window, but it’s usually between day 8 and day 14 of a 28-day cycle.

Things to do

  • HAVE ALL THE SEX – The more you do it, the better your chances of falling pregnant.
  • Choose the right lube – Avoid ones with sperm-inhibiting chemicals.

Week 3

While you won’t see or feel it happening, your egg will be fertilized this week.

You probably won’t notice any symptoms this early on, but it’s not unheard of to experience first trimester fatigue, nausea, tender breasts or increased urination.

Things to do

Week 4

You’re officially pregnant! While your baby is just a teenie tiny ball of cells, during this week the foundations of their nervous system, brain, hair, skin, muscles, skeleton and organs start to form. Wild!

It’s normal to experience spotting in first trimester weeks, also known as ‘implantation bleeding’. Cramping during first trimester, along with bloating and mood swings can start as early as week four. But you may not feel anything at all yet.

Things to do

  • Take a pregnancy test – It’s most accurate if you take it a few days after your period is due.
  • Make an appointment with your doctor – They’ll run further tests to confirm the pregnancy, and discuss your maternity care plan. 

Week 5

Welcome to first trimester pregnancy hormone fluctuations. Your body will produce more hCG (the pregnancy hormone) at this point, and your estrogen and progesterone levels will spike too.

First trimester bleeding may be experienced around week five due to implantation. While it’s quite common, check in with your doctor if you’re worried about bleeding. You could also have sore breasts, and first trimester cramps or bloating – not to mention a whole host of weird AF early pregnancy symptoms.

Things to do

  • Keep calm and carry on – Don’t worry if you have no first trimester symptoms to speak of. Everyone has a different experience, and you might be lucky!

Week 6

Halfway through Trimester One, your baby now has a heartbeat! And they’ll have tiny arms and legs starting to grow. 

With your hormones still in overdrive, you may experience symptoms like first trimester headaches, light-headedness, and changes to your taste or smell. It’s also common to experience nausea, food aversions or cravings.

Things to do

Week 7

Your little one has been doing some major growing, having doubled in size over the past week to now measure 10mm (around ⅜ of an inch). 

As for you, raging hormones will still make you feel like sh*t. Morning sickness may also be ramping up around now, ranging from light nausea to vomiting multiple times a day. 

Things to do

  • Eat lots of fruit and veggies – Continue to eat well, and increase your fruit and vegetable intake, particularly if you’re experiencing constipation in week seven.

Week 8

Your baby is starting to look less like a blob, and more like a baby! An ultrasound would now show distinct head, arms and legs forming.

You may continue to suffer from first trimester fatigue, tummy discomfort and overall ickiness. So take it easy, and focus on the magic happening inside you.

Things to do

  • Sneak some sleep in – Daytime naps never go astray, particularly if you’re suffering from first trimester insomnia (reported to affect about 44% of women).

Week 9

This week your baby is as big as a penny and he/she is even growing little toes!

Week nine is typically the peak point of morning sickness in pregnant women. While you may not be feeling great, take it as a sign your pregnancy is progressing as it should. And with any luck, it’ll ease up soon.

Things to do

  • Take it easy – Eating plain, dry crackers or toast may help with morning sickness, but if you’re struggling to keep food down have a chat with your doctor.

Week 10

Hey you! You’ve been doing some fantastic work growing a human. Your baby even has all their organs formed now.

If you’re feeling a little gassy, this is completely normal. Your progesterone levels are rising in an effort to loosen up your womb muscles, but in the process it may be triggering first trimester bloating and diarrhea. First trimester back pain can also be a result of the hormones surging through your body, loosening it up to prepare for more growth.

Things to do

  • Invest in your maternity wardrobe – By now you may be feeling your clothes getting tighter. Your bump may not be visible to others yet, but you can still treat yourself to maternity bras and looser clothing to prep for its arrival

Week 11

This week, your magnificent mama body will develop your baby’s genitals. They’ll weigh about ⅓ ounce (8 grams) – that is, the whole baby, not just their freakishly large genitals. 

You’ll probably be sticking close to the bathroom still, due to peeing up a storm and still managing morning sickness.

Things to do

  • Book your nuchal translucency test – This is a common first trimester screening test that can determine if your baby has a chance of developing chromosomal abnormalities. 

Week 12

While your first trimester symptoms should be starting to wane soon, you may still feel nauseous, tired and tender. 

Things to do

  • Catch up on your scans – If you haven’t already, book in for your 12/13 week first trimester ultrasound. This is one of the most magical pregnancy scans you’ll have, as you’ll see your baby in profile! (This is generally the shot that parents share in their pregnancy announcement posts.) 

Week 13

By now you’re wondering ‘how long is the first trimester?’ (read: WHEN WILL THIS HELL END?), and the answer is: next week. 

Many women experience increased hunger levels moving into the second trimester as your body requires extra nutrients to keep your bubba growing. Your first trimester weight gain will have been minimal, but get ready for things to really take off over the next few weeks as your baby gets bigger.

Things to do

  • Celebrate – You’ve officially reached the end of your first trimester. You did it! (Two more to go.)
  • Tell people (if you want to) – Many people wait for the end of the first trimester before letting others know about the pregnancy. Why this point? The risk of miscarriage declines significantly beyond this stage, and as your belly expands in the coming weeks it’ll become tougher to hide it! In saying that, we believe it’s important to reduce the stigma around pregnancy loss, so if you want to tell people as soon as you get those two pink lines, go for it mama! Whatever feels right for you. 

What a journey you’ve been on already! We hope you’ve enjoyed learning the ins and outs of what to expect in your first trimester. But please note, this article shouldn’t replace good medical advice from your care team. If you’re ever unsure or worried about your pregnancy and symptoms, have a checkup. You know your body. Trust your gut on this. 

Read next: Pregnancy week by week: your second trimester

National Health Service, UK, Vitamins, supplements and nutrition in pregnancy 

Healthline, 11 Foods and Beverages to Avoid During Pregnancy – What Not to Eat

Raising Children Network, You at two weeks pregnant

Healthline, What is ovulation? 16 things to know about your menstrual cycle

Optimizing natural fertility: a committee opinion, Fertility and Sterility, Volume 100, Issue 3,

2013, Pages 631-637, ISSN 0015-0282

Better Health Channel, Pregnancy Week by week

Flo Health, 3 weeks pregnant

Raising Children Network, You at four weeks pregnant

Mayo Clinic, Fetal development: The 1st trimester

Raising Children Network, You at six weeks pregnant

National Health Service, UK, You and your baby at 7 weeks pregnant 

Raising Children Network, You at seven weeks pregnant

R.M. Román-Gálvez, C. Amezcua-Prieto, I. Salcedo-Bellido, J.M. Martínez-Galiano, K.S. Khan, A. Bueno-Cavanillas, Factors associated with insomnia in pregnancy: A prospective Cohort Study, European Journal of Obstetrics & Gynecology and Reproductive Biology, Volume 221, 2018, Pages 70-75, ISSN 0301-2115,

Cleveland Clinic, Explaining the cruel injustice of morning sickness

Raising Children Network, You at ten weeks pregnant

National Health Service, UK, Week by week guide to pregnancy, first trimester, week 10 

Healthline, First trimester pregnancy back pain: causes and treatments

University of Michigan Health, Nuchal Translucency Screening Test

Medical News Today, What are the miscarriage rates by week?

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