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What to Expect in the First Trimester

Whether you or your partner are pregnant (huge congrats from Metanium HQ!), or you suspect you may be and want to know more, we’re here to tell all about what to expect in the first 13 weeks of your pregnancy!

Not every pregnancy is the same, but to give you a little guidance, here’s is a helpful first trimester guide about the changes to your body, common pregnancy symptoms, and how your little one will be developing week by week.

WEEKS 0 - 3  

The first trimester, weeks 0-13, will probably be the most life-changing and exciting weeks of your life - especially if it’s your first baby! The earliest and most common sign of pregnancy is missing a period, and by that time, you’ll most likely be around two weeks pregnant. The date of the first day of your last period is important as this is used to calculate your due date. If you’re currently trying for a baby, a top tip from us would be to track your cycle so your doctor can accurately guess when your little one should be arriving.

Between weeks 3 and 4 it’s unlikely you’ll experience many other symptoms, however by week 3, the egg has travelled along the fallopian tube towards the uterus and becomes an embryo. This new embryo then settles into the lining of the uterus for the next 9 months, and grows into a beautiful baby.



At week 4, you’ll be able to confirm your pregnancy using a home pregnancy test. Alternatively you can book an appointment with your GP or local family planning clinic, which we recommend either way as you can start to make your pregnancy care appointments with a midwife which usually start at week 8 onwards.

At this point, your baby is the size of a poppy seed. Although tiny, your baby has now snuggled itself into your womb and started to develop its nervous system and heart - it’s also attached itself to you with its own set of blood vessels, which will eventually become the umbilical cord. 

When it comes to your body, the following symptoms are common. Don’t worry if you aren’t experiencing them either, every pregnancy differs: 

  • Bloating
  • Cramping
  • Tired and moody
  • Sore or swollen breasts 
  • Nausea 
  • Frequent need to urinate



At around 7mm, your baby is now the size of a finger nails. Their hands and feet are still little buds, however this week your placenta should be growing, or become fully grown around the outside of the amniotic sac, meaning a rich blood supply can now fuel your little one’s development. 

You’ll most likely be experiencing some of the symptoms from week 4 still, along with potential food cravings or a sudden dislike to something you usually enjoy. As your body is working hard to grow your baby, although a common myth, there’s no reason to ‘eat for two’ until your final trimester - and even then you only need to increase your intake by around 200 calories a day. Find out more about common pregnancy myths here. 



Your baby’s heart should start to beat, just in time for you to hear it at your first scan - and trust us, you’ll treasure that moment forever! As their spine and shape start to develop, your baby at this stage will look like a tiny tadpole, with a tail and everything!

Week 6 also tends to bring on the most well-known pregnancy symptoms - morning sickness. Despite its name, morning sickness can happen at any time of the day, and completely varies in severity between each mother. Morning sickness is very common in the early stages of pregnancy, with the main symptoms being vomiting and nausea. In some cases it can really affect your day to day life, and it’s never a nice experience for an expecting mother! It’s important to ask your friends, family and work colleagues for support during this time. 

Although there aren’t any proven remedies for morning sickness, these are some things that our Metanium parents have said have helped to ease their nausea in the past:

  • Sparkling water
  • Sucking ice cubes
  • Small frequent meals
  • Travel wristbands
  • Foods and drinks that contain ginger (like ginger biscuits, chamomile and ginger tea, ginger ale and crystallised ginger).

If your morning sickness is getting you down, or your symptoms prevent you from eating for 24 hours, contact your midwife or GP.




At week 7, your little one’s head will start to grow larger than their body, and cartilage starts to form in their teeny arm and leg buds, which starts the process of growing their cute little hands and feet! Morning sickness can last throughout the 1st trimester, so you’ll most likely be feeling a little nauseous, but the most common symptom to occur at week 7 is an increase in thirst. As the volume of blood in your body increases you may feel thirstier than usual, so it’s important to stay hydrated for both you and your baby. We recommend drinking 6-8 medium glasses of water a day.



By week 8 your baby will have had a massive growth spurt and started to look more like a little person. At the size of a raspberry, your baby is referred to as a foetus. You’ll also be ready for your first ultrasound which normally happens between weeks 8 and 12, an exciting moment for any parent!



Your baby will now be the size of a strawberry, which is appropriate as their taste buds will have started to form on their tongue! Colour will start appearing in their eyes too, and although you can’t find out the gender until around 18-21 weeks, their genitals do start to develop at 9 weeks - if you’re planning a gender reveal party, here's where to start preparing! 

In the first trimester your body will experience a high rush of pregnancy hormones like progesterone and oestrogen, which can bring on a roller coaster of emotions - so if you’re quick to snap or feel a little more teary than usual, it’s completely normal. We recommend a high dose of ‘me’ time and a long hot bath to help ease this!



Your baby or foetus will now be around 30mm long, which is about the size of a small apricot. Your baby’s eyes and ears will be starting to form, and their mouth will now have a delicate upper lip. A tiny nose will also be visible, along with a more defined jaw bone which contains teeny versions of all your baby’s milk teeth! 

At 10 weeks, if not already, your morning sickness may make you feel lethargic and tired during the day. It’s tempting to reach for some biscuits or chocolate to perk you up, but we recommend you opt for healthier snacks like fruit or hummus and vegetables, as it keeps your blood sugar stable which can help to battle any fatigue.



At the size of a fig, your baby’s head is still a little supersized, but the body is working hard to catch up - so they’ll look almost human now! Fingers and toes are losing their webbing and spreading out, so you’ll soon be getting a little wave from inside your belly. Although the baby will be kicking around at this point, you won't be able to feel anything for several weeks. 

If you’re a second time parent you may start to show a little earlier than you did with your first baby, as your body has muscle memory and can adapt to your baby’s environment quicker. However, if it’s your first pregnancy, it’s unlikely your bump will be obvious to other people until the second trimester. 

As your baby grows, your body will pumping more blood around to feed your baby, which may make you feel a little hot, sweaty or dizzy - don’t worry, this is just your baby’s way of telling you to put your feet up and have a drink of water. 



At week 12 there’s a good chance your placenta should be fully grown and helping to feed your baby. This leads to your hormones balancing out a bit, so you may feel a little more in control of your emotions towards the end of your first trimester. To prepare for your baby’s growth, your waist will be becoming thicker and your breasts will most likely be becoming larger - this is caused by hormones already preparing your body to produce milk!

Your baby will now be about the size of plum, with an average weight of 18g, equivalent to if you were holding three grapes - amazing, right? At this stage your baby has developed everything it needs to, from internal organs and muscles, to a full skeleton made up of tissue which will now harden into bone. Your baby’s only job now is to keep on growing!



You’re now a third way through your pregnancy - how exciting! Hopefully most of your morning sickness symptoms have subsided but if not, we promise you your gorgeous little baby will be worth all the symptoms in the world. A small baby bump may be visible, which should ease the need to pee as frequently - as your womb continues to grow upwards and outwards, your baby no longer rests as much on your bladder! 

Your baby finishes the first trimester at the size of a peach and to celebrate makes its first jerky movement inside of your stomach. Again, although you won’t feel them, you may see on your ultrasound little hands finding their way into a mouth, or some babies even suck their thumbs in the womb! It's not only cute to watch but it actually helps to develop their sucking reflex for feeding time once out of the womb!

Let us know if you found this article helpful over on Facebook or Instagram - would you like to hear from us about the second trimester?


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