First Trimester of Pregnancy: 0-12 Weeks
Congratulations and welcome to the first trimester of pregnancy. The first stage of this journey may be a bit of a rollercoaster ride, but that’s hardly surprising as something amazing is happening deep down in your belly.
By the end of this trimester, a bundle of cells inside your uterus will have developed into a fully formed foetus with all the organs muscles, limbs and bones in place – everything your little one needs to keep on growing and maturing for the rest of your pregnancy until he or she is ready to be born.
You probably have some questions about what’s in store over the coming weeks and months. That’s why we’ve put together some handy information about how your little one is growing and what you as a parent-to-be can expect, along with some tips for this important period
How Long Is the First Trimester?
The first trimester lasts about 12 weeks, and it actually starts before you actually got pregnant. This is because your estimated due date is usually calculated from the first day of your last menstrual period.
If you haven’t been to see your doctor or a midwife yet, you can use our Due Date Calculator to get a quick estimate of your due date. Once you do get to your doctor, they will be able to give you an estimate of how far along you are, too.
Your Baby’s Development in the First Trimester
During the first trimester of pregnancy, what starts as a tiny bundle of cells quickly turns into a foetus that's about the size of a plum. In these three months of pregnancy, your little one’s brain, spinal cord, heart, and tiny limbs — complete with fingers and toes — will form.
Meanwhile, your uterus is becoming a comfortable home for your little one. At first, your little one gets all the sustenance needed to grow from a yolk sac that surrounds him or her. Around the end of the first trimester, however, the placenta and umbilical cord will take over the job of nourishing and supplying oxygen to your foetus.
By the end of third month of pregnancy, your little one is fully formed, with all the organs, muscles, limbs and bones in place, but all in teeny-tiny size – there’s still a lot of growing to do.
There’s a lot going on in the first trimester, but here are a few of the most exciting milestones:
4 Weeks: Implantation
After the egg is fertilised at around four weeks pregnant, it becomes a cluster of rapidly dividing cells. This cluster of cells travels the rest of the way along the fallopian tube, and burrows into the lining of your uterus.
When this happens, the outer cells start to form connections with your blood supply, while the inner bundle of cells splits into two, then three layers of cells that will form the various parts of your little one’s body:
The innermost layer of cells will become the lungs, stomach and other parts of the digestive and breathing system
The middle layer will eventually form the muscles, bones, heart and circulatory system
The outer layer becomes the brain and nervous system, skin, nails, tooth enamel and eye lenses
6 Weeks: Taking Shape
Around six to seven weeks into the first trimester, your embryo – which is what your little one is called at this stage – has a bulge where the heart is forming, and a bump at one end that will become the head.
What was once a ball of cells now has a tail and a layer of thin, transparent skin, and is curved into a c-shape.
The head bump already has little dimples where the ears will form, and thicker patches mark where the eyes will be.
There are also small swellings known as ‘limb buds’, which are the beginnings of your little one’s arms and legs.
If you were to have a vaginal ultrasound scan at six weeks pregnant there’s a chance that you’d be able to see a tiny heartbeat.
9 Weeks: Not Just a Pretty Face
At 9 weeks your little one is now known as a foetus, which just means ‘offspring’ in Latin.
Your little one’s face is forming now. The eyes are bigger and starting to gain some colour, and your foetus now has a mouth and tongue, complete with taste buds.
The hands and feet are taking shape, too, although at this time there are only grooves where the fingers and toes will be.
10 Weeks: Shaking and Moving
At this stage of the first trimester, your little one is moving around. These jerky movements are visible on an ultrasound scan at 10 weeks pregnant, but you probably won’t feel any movement yourself until sometime around or after 16 weeks.
Keep in mind that nobody can tell just when those first flutters will come, and it may be a little later for you – especially if you’re a first time mum-to-be. Don’t be surprised if you have to wait several weeks more, and don’t hesitate to ask your doctor for more personalised guidance on when you might first feel your little one move.
The facial features are also becoming more prominent. There are two tiny slits which are the nostrils and the upper lip is in place.
Amazingly, your little one’s growing jawbones are already home to what will eventually become baby teeth.
11 Weeks: Heart to Heart
Your little one’s heart is fully developed once you’re 11 weeks pregnant, and it’s pumping quickly – at a rate of around 180 beats per minute.
This is probably two or three times as fast as yours, although your own pulse is sure to quicken if you glimpse your little one at your next ultrasound scan.
What's Going On in the First Trimester
Are you experiencing one or more of the typical first trimester pregnancy symptoms, but still aren’t sure if you're actually pregnant? A home pregnancy test can help clear up any doubts, and your doctor can also confirm your pregnancy.
Some mums-to-be find the first trimester of pregnancy quite challenging. You could be in for a ride on an emotional rollercoaster, as the rush of hormones in early pregnancy can trigger more intense mood swings than you may be used to.
Remind yourself that it’s OK to feel what you’re feeling, even if it’s not what you thought you would feel. Your moods may swing from being happy and excited to feeling overwhelmed and anxious, and everything in between.
Talk to your loved ones and your doctor or midwife about your feelings during this trimester, at any other stage of pregnancy, and even beyond.
We cover some of the main first trimester symptoms in more detail below.
The good news? Each symptom is a reminder that you’re bringing a new life into the world, and each week of pregnancy brings something interesting and new.
It may also help to remind yourself that these symptoms won’t last forever. In fact, it’s common for the early symptoms of pregnancy to subside in the second trimester, and this may even be accompanied by a welcome burst of extra energy.
Stay up-to-date with all these exciting changes by downloading our Pregnancy Guide. It's packed with information to help you get through the first trimester, and the following two as well.
Here, you’ll be given a more accurate estimate of your due date, and how many weeks pregnant you are.
The purpose of the scan is also to check for certain abnormalities that may be detectable via ultrasound, such as spina bifida.
You may also be offered optional screening tests for other complications, such as Down’s syndrome. These are optional. Your doctor or midwife will be able to tell you more about what’s involved.
There’s a small chance that you’ll come away from the dating scan with a little more than you bargained for, as this is usually when you’ll find out if you’re pregnant with twins, triplets or more.
First Trimester Symptoms
The symptoms you experience in the first trimester can vary from week to week. Also, the symptoms you experience during this pregnancy might differ from what you experienced in a previous pregnancy.
Here are some of the most common symptoms you might encounter during this trimester:
Tender breasts. In the early part of your pregnancy, pregnancy hormones could be making your breasts heavier, and a little sore or tender. You could also experience a tingling sensation. With all that extra blood to carry around your body, your veins may be more visible through your skin. Meanwhile, those hormones may also make your skin, moles and birthmarks or your nipples a little darker. Most of these changes gradually fade away after birth, although your nipples may stay be a little darker than before.
Fatigue. Feeling tired or exhausted is particularly common in the first trimester, as your hormones go into overdrive. The best thing you can do is get plenty of rest. Keeping to a healthy diet and doing gentle exercise might also help you feel better. Your doctor or midwife can give you personalised advice on the kind of pregnancy diet to follow to suit your calorie and nutritional needs, and what exercises are safe for you to do at this time.
Implantation bleeding. After conception, as the fertilised egg burrows into the lining of your uterus, you may experience some light cramping and spotting. This is more likely to occur around the time of your first missed period. Although, implantation bleeding is nothing to worry about, it’s always safest to get in touch with your doctor if notice any bleeding during your pregnancy.
Nausea. The queasiness (and sometimes vomiting) known as morning sickness usually appears in the first trimester. Contrary to its name, though, it doesn’t strike only in the mornings! Try to think of morning sickness as a reassuring reminder that you are pregnant. You might be able to ease some of the symptoms with a few lifestyle changes, like avoiding food or smells that trigger your nausea, and eating smaller, more frequent meals of plain, low fat foods. You may find cold foods easier to stomach than hot meals. Food or drink that contains ginger may also help take the edge of your queasiness, but ask your doctor, midwife or pharmacist before taking ginger supplements.
Frequent urination. The hormonal changes you experience in the first trimester may result in your needing to pee more often than usual in the first trimester of pregnancy. Don’t drink less water, because it’s important to stay hydrated. Instead, you might just need to plan ahead a little more to ensure you always have a loo nearby.
Thicker, shinier hair. Some mums-to-be find that the extra oestrogen coursing around their bodies makes their hair more luxuriant in the first trimester. This could be one of the more welcome symptoms of pregnancy!
Hormonal acne. An increase in oil production triggered by hormones can clog pores and lead to acne in some mums-to-be.
Cravings. It’s not unusual to have hankerings for strange foods when you’re pregnant. Or you may find that you suddenly can’t stomach items that you used to enjoy eating or drinking. It’s usually fine to give in to cravings from time to time, as long as you keep to a healthy diet overall. If you start to crave any non-food items like dirt or coal, tell your doctor or midwife straight away. This could be a sign of an iron deficiency known as pica, which can be dangerous if it isn’t treated straight away. Read more about how to get the right amount of iron and calcium (another important mineral) in your diet.
FAQs at a Glance
What foods should I avoid during my first trimester?
Some foods that it’s better to steer clear of while you’re pregnant include:
Soft blue cheese and soft cheese with white rinds
Raw or partially cooked eggs (except eggs with the Lion Mark stamped on their shell)
Pâté (all kinds, including vegetable pâté)
Raw or undercooked meat
Cold cured meats, like salami, prosciutto or chorizo
Unpasteurised dairy products.
Do I need pregnancy vitamins?
A healthy diet is a great start, but taking a folic acid supplement can help support the growth and development of your little one and can help prevent complications in the first trimester. You may be able to get some minerals like calcium and iron in your food, but in some cases your doctor may advise taking supplements. It might also be worth considering taking vitamin D supplements. Ask your doctor or midwife what pregnancy vitamins are best for you.
Can I have a flu jab while pregnant?
Checklist for This Trimester
Read up on what foods and drinks to avoid during pregnancy.
Learn about the benefits you may be entitled to when you’re pregnant, such as free prescriptions and dental care on the NHS, ‘Healthy Start’ vouchers, or maternity leave.
Find out if your partner is eligible for paternity leave, and how to claim it. Your midwife may be able to help you with this.
Start buying or researching some of these essential items of baby gear.
Ask your doctor or midwife about taking folic acid and pregnancy vitamins.
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