First Trimester of Pregnancy: 1-13 Weeks

First Trimester of Pregnancy

Congratulations! If you’re in your first trimester, you're at the beginning of a wonderful pregnancy journey. At this stage, it’s natural to have many questions about what’s in store in the weeks and months ahead. In this article, we’ve covered some essential information on the first trimester weeks, some common early pregnancy symptoms, how your baby is developing, and a few tips to help you along the way this trimester.

Highlights From the First Trimester of Pregnancy




1st Trimester Highlights
Fetal Development
  • Many little cells work together to become an embryo and then a fetus.
  • A brain, spinal cord, heart, and tiny limbs start to form.
Potential Symptoms
  • Changes in breasts and skin
  • Fatigue
  • Nausea
  • Mood swings
1st Trimester TipMake some healthy lifestyle choices— eating well, getting regular exercise, and avoiding smoking and alcohol.



First Trimester Weeks: How Long Is the First Trimester and When Does It End?

Are you wondering what is the first trimester of pregnancy, how many weeks are in this trimester, and when it’s over? Well, the 1st trimester is about 13 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 full-term pregnancy is roughly 40 weeks long, so your healthcare provider will calculate 40 weeks from the start of your last period to estimate your due date. If you haven't been to your provider yet, you can use our Due Date Calculator located above to get a quick estimate. Keep in mind that most babies aren’t born on their due date, which is only an estimate. Rather, they’re typically born in the two-week period before or after the date. Your pregnancy is considered full-term at the start of 39 weeks. So, when does the second trimester start; week 13 or 14? At week 14, you’ll enter your second trimester. The three trimesters of pregnancy are composed of 40 weeks. Take a closer look at what happens during each individual week of pregnancy with our pregnancy calendar, including the weeks in the first trimester.

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 fetus that's about the size of a large plum. In these first couple of 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, who will be nourished by the developing placenta and umbilical cord. By the end of the 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. Keep reading to learn about a few of the most exciting fetal development milestones during the first trimester weeks.

4 Weeks: Implantation

The ball of rapidly dividing cells, called a blastocyst, implants in the uterus. This is when some pregnant people experience implantation bleeding in the first trimester, which is generally a light spotting.

The inner cells will become the embryo, and the outer cells will become the placenta. The placenta will provide nourishment to your baby from now until delivery.

6 Weeks: Taking Shape

Around weeks 6 and 7, the heart, lungs, and other key organs start to develop, and the head and limbs also take shape. What was a ball of cells just weeks ago is forming a more recognizable C-shape.

9 Weeks: In Motion

At about 9 weeks, your little one, now known as a fetus, may start moving around. However, you probably won't be able to feel any movement until the second trimester.

10 Weeks: Fingers and Toes

This week, your baby's fingers and toes begin to lose their webbing and continue to grow longer. It won't be long until you're able to count them!

10 to 12 Weeks: Cardiac Activity

At around 10 to 12 weeks, you and your healthcare provider may be able to hear your baby’s cardiac activity with a handheld Doppler device during one of your checkups.

Illustration of Fetal Development Week by Week

Take a look at the illustration below to understand how your little one may develop week to week during the first trimester:

What’s in Store for You in the First Trimester?

During the first trimester, you may make some discoveries and decisions and experience various changes. Here are a few examples:

  • 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, but head to your healthcare provider if you’re in any doubt.

  • Determining your due date. Once you’ve confirmed your pregnancy, you’ll be eager to know when your baby will arrive, so take a look at our handy Due Date Calculator above. It 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 healthcare provider can also give you an estimated due date.

  • 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 some ways to tell your partner you’re pregnant. Whether you go with something funny, romantic, or downright creative, your partner will love the surprise!

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

  • Experiencing shifting emotions. Some find the first trimester of pregnancy quite challenging. Pregnancy hormones can trigger more intense mood swings than you may be used to. Having different feelings than you thought you would about your pregnancy is also perfectly natural. We cover these emotional changes and suggest ways to cope with mood swings in the next section.

  • 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.

  • Going to your first prenatal care checkup. As soon as you know you're pregnant, schedule your first visit with your healthcare provider. You’ll have checkups in the first trimester and throughout your pregnancy. Your provider can monitor your health and that of your baby and check for signs that your pregnancy is going well in the first trimester, such as your baby’s development being on track. At this first visit, your provider will ask you lots of questions about your medical history, run tests, do a physical exam, and give you an estimated due date. Your provider will also be able to give you an idea of when future checkups and exams will take place. Prepare a list of questions beforehand so you come away from this first checkup with all your questions answered and know who to call outside of hours in case you have an urgent question or concern.

  • Having tests and ultrasounds. In the first trimester, you may be offered at least one ultrasound scan. Using ultrasound, your healthcare provider 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, and these tests typically include 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 risks 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 provider can explain your options to you, including any risks and benefits, so you can make an informed choice.

  • Learning you’re having twins. There’s a small chance that you’ll come away from 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 more than one, read our guides to pregnancy with multiples.

  • 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 parents in your area, who will have lots of personal insights and valuable experiences to share. The Pampers website is also packed with information and tips about pregnancy and the first three years of your little one’s life.

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

  • Making some healthy lifestyle changes. Adopting healthier habits in the first trimester is important not only for you but also for your baby. If you haven’t done so already, start following a healthy, balanced diet to help with morning sickness and cravings and to keep your pregnancy weight gain on track in the first trimester and onwards. Speak to your healthcare provider about your calorie and nutritional needs during pregnancy and ask about prenatal vitamins. Alcohol, smoking, and drugs can be harmful, so it’s best to steer clear of these. As for those life-saving coffees (and chocolate bars), the recommendation is to limit your caffeine intake to 200 milligrams a day, the equivalent of a 12-ounce cup of coffee. Start exercising in the first trimester or keep up with your regular exercise routine after checking with your provider to learn what exercise is safe for you to do during pregnancy. Gentle exercise in the first trimester and beyond, such as yoga can help ease the discomfort of lower back or round-ligament pain as your body grows and changes.

  • Resting and relaxing. Building a new life can be tiring. And you've got two more trimesters to go before you meet your baby, so conserve your energy.

What Weeks and Months Are in the First Trimester?

You may be wondering which weeks and months make up the first trimester. When the weeks of pregnancy are grouped into months, there’s some variance in how this is done. This is because 40 weeks can't be divided neatly into nine months and because months typically are a little longer than four weeks. But if you’re wondering how many months is the first trimester, it’s generally considered to be about three months long, or 13 weeks, as we mentioned above.

Check out our visual below to see what’s included and to get an idea of how your belly may be growing:

First Trimester Signs and Symptoms

Although every pregnancy is unique, here are some of the most common signs and symptoms of the first trimester:

  • Emotional ups and downs. The first stage of this journey may feel like a roller coaster ride, but that’s hardly surprising as something amazing is happening in your belly, and you’re at the start of a new adventure. The rush of hormones in early pregnancy can also trigger 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.

  • Changes in breasts and skin. Pregnancy and pregnancy hormones can trigger many changes in your body during the first trimester and throughout pregnancy. Hormones could be making your breasts heavier and a little sore or tender. 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, birthmarks, or even your nipples a little darker. Most of these changes gradually fade away after you give birth.

  • Fatigue. Feeling tired or exhausted is particularly common any time during the first trimester, as your hormones go into overdrive. The best thing you can do if you’re experiencing pregnancy fatigue is to get plenty of rest. Maintaining a healthy diet and doing gentle exercise might also help you feel better throughout your pregnancy. If you’re suffering from insomnia in your first trimester or throughout pregnancy, talk to your provider for some advice.

  • Nausea. The nausea (and sometimes vomiting) known as morning sickness may appear 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're pregnant. So, what helps morning sickness in the first trimester? You might be able to ease some of the symptoms with a few lifestyle changes in the first trimester and throughout your pregnancy, 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 drinks that contain ginger may also help take the edge off your queasiness.

  • Cravings. Weird as they are, cravings for unusual foods are usually nothing to worry about. However, talk to your healthcare provider right away if you start to crave non-food items like soil or paper.

  • Frequent urination. With rapid hormonal changes and your body’s organs working harder than usual, you may find yourself needing to pee more often than usual during the first trimester.

  • Acne. An increase in oil production triggered by hormones can clog pores and lead to acne in some pregnant people. Wash your face twice a day with a mild cleanser, go for oil-free cosmetics and sunscreens, and ask your healthcare provider about any over-the-counter products or medications that can help reduce breakouts.

  • Bloating. As we mentioned before, those pesky pregnancy hormones can trigger many symptoms in the first trimester, and one of those is bloating. First-trimester bloating may feel similar to when you’re about to start your period, and it may cause you to think you have an early pregnancy belly already. However, you probably won't notice much of a belly this early on in pregnancy.

Precautions to Take During the 1st Trimester of Pregnancy

During your 1st trimester of pregnancy, it’s important to take precautions and prioritize your health and that of your developing baby. Here are some considerations to keep in mind now and throughout your pregnancy journey:

  • Steer clear of alcohol, tobacco, second-hand smoke, and illicit substances, as they can pose serious risks to your baby's health and lead to complications.

  • Be mindful of your caffeine intake and limit it to less than 200 mg a day. Caffeine can be found in chocolate, some teas, colas, and, of course, coffee.

  • Avoid foods such as raw or undercooked seafood, raw eggs, unpasteurized milk, and soft cheeses.

  • Check in with your healthcare provider before taking any prescription and over-the-counter medications.

  • Be cautious of hazards that you may be exposed to in your environment, such as harmful ingredients in pesticides, cleaning products, and materials in your workplace.

  • Minimize exposure to radiation, including X-rays and other medical imaging techniques, unless it is absolutely necessary.

  • Engage in gentle exercise during pregnancy, checking with your healthcare provider to ensure that what you're doing is safe for you and your baby.

  • Avoid saunas and hot tubs, as high temperatures may be harmful to your baby.

Remember, your healthcare provider is there to support you during this important time. Don't hesitate to reach out if you have any concerns or questions.

When to Contact Your Healthcare Provider

It’s essential to stay in touch with your healthcare provider throughout your pregnancy, particularly during the critical first trimester, and to go to all of your prenatal checkups. While some discomforts, like morning sickness or fatigue, are considered normal during the first trimester of pregnancy, certain symptoms may warrant immediate contact with your healthcare provider. These include the following:

  • Persistent severe abdominal pain

  • Heavy bleeding or spotting

  • Severe dizziness or fainting

  • Sudden severe swelling in your hands, feet, or face

  • Consistent severe headaches

  • High fever or chills

  • Difficulty breathing

  • Persistent vomiting or inability to keep down fluids

  • Signs of dehydration (dry mouth, not urinating regularly, feeling dizzy when standing up)

  • Blurred vision or spots before your eyes

  • Any other symptom that feels unusual or concerns you.

Remember, your healthcare provider is your best resource for any questions or concerns you may have during your first trimester of pregnancy. It's better to be safe and reach out, even if you're unsure whether your symptoms are cause for concern.

Checklist for the First Trimester

Here’s a checklist of things you may wish to do in your first trimester of pregnancy:

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

  • Ask your provider what tests or scans are recommended for you based on your medical history, and mark these in your calendar.

  • Get a flu shot and get caught up on any other immunizations you're missing.

  • Consider whether genetic testing like nuchal translucency screening and chorionic villus sampling (CVS) are tests you may like to have during the first trimester of pregnancy.

  • Consult your healthcare provider about taking folic acid and prenatal vitamins.

  • Ask your healthcare provider if the medications you currently take for things such as headache relief are safe during the first trimester of pregnancy.

  • Find out what maternity or paternity leave you and your partner may be eligible for.

  • Review your health insurance policies to check you have the coverage you want and need. If you don't have insurance for yourself or your baby, check with your Primary Health Care Services to find out what is available.

  • 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 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 perhaps pick a day of the month for taking monthly progress photos.

  • Just for fun, guess your babies’ gender in our fun quiz.

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


If you’re suffering from morning sickness in your first trimester, include easy-to-digest foods in your diet like bananas, rice, applesauce, and toast—this can also help ease heartburn and indigestion. Taking a daily prenatal vitamin may also help reduce the risk of severe pregnancy-induced nausea. You can also try ginger in the form of ginger ale, tea, or candies to help settle your stomach during periods of nausea.

The Bottom Line

The first trimester of pregnancy is full of excitement and anticipation. By following our guidelines and your healthcare provider's advice, you can make your pregnancy a little easier. Listen to your body, prioritize self-care, maintain open communication with your provider, and don't hesitate to reach out if you have any concerns or uncertainties. This beautiful journey is just beginning, and now is a great time to create a nurturing environment that will support your baby’s growth and development.

How We Wrote This Article The information in this article is based on expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. 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.