First Trimester of Pregnancy: 0-12 Weeks

Welcome to the first trimester of pregnancy. This is the start of a wonderful journey, and it’s natural to have lots of questions about what’s in store for you in the weeks and months ahead. We’ve compiled some essential information on foetal development during the first trimester, common early pregnancy symptoms and what kinds of things are in store for you this trimester.

When Does the First Trimester Start and How Long Is It?

The first trimester is about 12 weeks long, and it actually starts before you become pregnant. This is because your estimated due date is usually calculated from the first day of your last menstrual period (LMP). A normal pregnancy is about 37 to 42 weeks long, and your doctor will calculate 40 weeks from the start of your last period to estimate when you’re due. If you haven't been to your doctor yet, you can use our Due Date Calculator to get a quick estimate. Keep in mind that most babies aren’t born exactly on their due date, which are only estimates. Rather, they are typically born in the week before or after the date. Your pregnancy is considered full term at 37 weeks. The trimesters of pregnancy are composed of 40 weeks. Take a closer look at what happens during each individual week of pregnancy. The weeks of pregnancy are sometimes broken down into months, but there’s some variance in how the weeks are grouped into months. This is because 40 weeks don’t divide neatly into 9 months, and because months typically are a little longer than 4 weeks.

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 an embryo and then a foetus that's about the size of a large plum. In these first few weeks 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, the embryo gets all the sustenance needed to grow from the surrounding yolk sac. 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, all essential organs and body parts will be in place — albeit in teeny-tiny size. There’s a lot happening in the first trimester. Here are a few of the most exciting foetal development milestones:

4 Weeks: Implantation

After the egg is fertilised at around four weeks pregnant, it becomes a cluster of rapidly dividing cells called a blastocyst. This cluster of cells travels the rest of the way along the fallopian tube and burrows into the lining of your uterus. This is when some mums-to-be experience implantation bleeding. During this time, you may experience some light cramping and spotting. 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. When implantation 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, the 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, which 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: In Motion

At nine weeks your little one is now known as a foetus, which just means ‘offspring’ in Latin. Your little one’s face is forming. 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 about 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. Experts say feeling foetal movement for the first time can happen anywhere from 16 to 24 weeks. Around this week, 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.

Illustration of Foetal Development Week by Week

Click through the illustrations below for a visual representation of how your little one develops week to week during the first trimester:

What’s in Store for You This Trimester

Here are just some of the things you may be doing or that may be coming your way in the first trimester:

  • Confirming your pregnancy. If you’re experiencing early pregnancy symptoms, but are still not sure if you're actually pregnant, a home pregnancy test can confirm your hunch.

  • Determining your due date. Once you’ve confirmed your pregnancy, you’ll be eager to know when your baby will arrive. Our Due Date Calculator can give you an estimate of when your baby will be due based on the first day of your last menstrual period or the date of conception. Your doctor or midwife can also give you an estimate of your due date and how far along you are.

  • Going to your first antenatal care checkup. As soon as you know you are pregnant, schedule your first visit with your doctor or midwife. This will be just the first of many checkups during your pregnancy when you and your foetus’s health can be monitored. At this initial visit, you’ll be asked lots of questions about your medical history. Tests and a physical exam will happen. You’ll also be able to learn when doctor’s appointments will be. Prepare a list of questions beforehand so you come away with all your questions answered. Before you leave the appointment, find out who to call outside of hours in case you have an urgent question or concern.

  • Having tests and ultrasounds. In the first trimester you’ll likely be offered at least one ultrasound scan. Using ultrasound, your doctor can give you a more accurate estimate of your due date, and how many weeks pregnant you are. You may also be offered screening tests for certain genetic conditions. These tests typically include both a blood test and an ultrasound scan. These screening tests are optional, and it's important to note that they don't diagnose any particular conditions; rather, they evaluate the possible risk of various conditions. After a screening test, you may choose to have more thorough diagnostic tests done. Which, if any, screening and diagnostic tests to do is a personal choice. Your doctor can explain your options to you, including any risks and benefits, so you can make an informed choice.

  • Announcing your pregnancy to your partner. If your partner doesn’t already know you’re pregnant, you may be looking for fun ways to reveal the special news. Here are nine ways to tell your partner you’re pregnant. Whether you go with something funny, romantic or downright creative, your partner will love this surprise!

  • Considering when to tell others. When to share the news of your pregnancy with loved ones is a personal choice, but some mums-to-be prefer to wait until the end of the first trimester or the start of the second. If you’re wondering when to tell your colleagues or employer, your doctor can give you personalised advice.

  • Experiencing shifting emotions. Some mums-to-be find the first trimester of pregnancy quite challenging. Pregnancy hormones 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, your doctor or midwife about your feelings whether it’s now, later on or even after your baby’s birth.

  • Working through pregnancy symptoms. You may have to deal with some annoying first trimester symptoms — more on these 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 burst of extra energy.

  • Learning you’re having twins. There’s a small chance that you’ll come away from a your first trimester ultrasound with a little more than you bargained for. Typically, an ultrasound can show if you’re pregnant with twins, triplets, or more by the time you’re 12 weeks pregnant. If you do happen to be pregnant with multiples, read our FAQ on twin pregnancy.

  • Becoming informed. If this is your first baby, doing some research on pregnancy, childbirth and child development might help you feel calmer and more in control of what’s to come. In addition to reading up on these topics, you might also like to speak with other mums in your area, who will have lots of personal insights and valuable experience to share. The Pampers website is also packed with information and tips about pregnancy as well as baby and toddler development. For now, why not check out our article on warning signs not to ignore during pregnancy.

  • Discovering how a second pregnancy may be different. If this isn’t your first pregnancy, you may be wondering how things could be different this time round. Read our article on differences you may experience during a second pregnancy.

  • Making some healthy lifestyle changes. Adopting healthier habits now is important not only for you but your developing foetus as well. Eat a healthy, balanced pregnancy diet and ask your doctor whether you need to take any prenatal vitamins. Alcohol, smoking and drugs can be harmful, so it’s best to steer clear of these. As for those life-saving coffees, the recommendation is to limit your caffeine intake to 200 milligrams of caffeine a day. Get moving after checking with your doctor what exercise is safe for you to do during pregnancy.

  • Resting and relaxing. Building a new life takes a lot of energy. And, you've got two more trimesters to go before you'll meet your baby, so conserve your energy.

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 of the first trimester:

  • Emotional ups and downs. The first stage of this journey may be a bit of a rollercoaster ride, but that’s hardly surprising as something amazing is happening in your belly and you’re at the start of a new journey. You may experience more intense mood swings than you may be used to. Don’t be surprised if you feel a little differently about being pregnant than you had expected. Aside from feelings of joy and excitement, you might also have worries or concerns about how pregnancy and having a baby will change your life. It’s helpful to talk about these feelings, either with a professional or with your support network of friends and family.

  • Headaches. Many mums-to-be get headaches in the first trimester. Ask your doctor about what pain killers may be safe for you take.

  • Stomach pain. You may experience stomach pain during the first trimester. It’s usually nothing to worry about if it feels only mild and goes away when you change position, rest, do a poo or pass wind. If it’s combined with symptoms like vaginal bleeding, lower back pain, a burning sensation when you pee or if the pain is severe and doesn’t subside after some rest contact your doctor for personalised guidance.

  • Changes in breasts and skin. Pregnancy hormones can make your breasts heavier and a little sore, tender or tingly. With all that extra blood to carry around your body, the veins may be more visible, too. Meanwhile, those hormones may also make moles, birthmarks and your nipples a little darker. Most of these changes gradually fade away after birth, although your nipples may stay 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 pregnancy 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.

  • 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.

  • 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.

  • 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.

  • Hormonal acne. An increase in oil production triggered by hormones can clog pores and lead to acne in some mums-to-be. Wash your face twice a day, go for oil-free cosmetics and ask your doctor about any medications that can help reduce breakouts.

  • 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!

FAQs at a Glance

Experts recommend that you limit your intake to about 200 milligrams of caffeine per day when pregnant. Don’t forget there is caffeine in coffee as well as some teas, dark chocolate and cola.

Checklist for the First Trimester

  • Find a good obgyn who can help you throughout your pregnancy and during childbirth. Make your first appointment as soon as you know you're pregnant.

  • Ask your doctor what tests or scans are recommended for you based on your medical history, and mark these in your calendar. Think about whether you’d like any additional optional genetic screening or diagnostic tests.

  • Ask your GP when you can get the flu shot.

  • Consult your doctor about taking folic acid and other prenatal vitamins.

  • Ask your doctor if the medications you currently take are safe during pregnancy.

  • Though this is a rare condition, you may want to read up on the signs of an ectopic pregnancy just in case.

  • Read up on maternity leave and paternity leave.

  • Find out what free medical care you are eligible for under the NHS. For example, you may be able to get free prescriptions and dental care among other benefits.

  • Make an appointment with your dentist to ensure you get good dental care during your pregnancy.

  • As your breasts grow, go for a bra fitting at your local retailer to ensure you’re in the right size.

  • Start a pregnancy journal or memory book if this is something you think you would like to look back on in the years to come.

  • If you would like to, take your first belly picture and decide on which day of each month you would take your progress photos.

  • Although you’ll have to wait to find out whether you’re having a boy or gir, just for a little fun now, guess your baby’s gender.

  • Start brainstorming name ideas and start putting a short list of baby names together.

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How we wrote this article
The information in this article is based on the expert advice found in trusted medical and government sources, such as the National Health Service (NHS). You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.

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