Trimester 1

Welcome to the first trimester of pregnancy. We've compiled 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 is about 13 weeks long, and it actually starts before you're pregnant. In fact, the first day of your last menstrual period is considered the beginning of week one of pregnancy. 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 give you an estimated due date. If you haven't been to your provider yet, you can use our Due Date Calculator to get a quick estimate.

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 fetus 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, 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 this trimester, but here are a few of the most exciting milestones:

4 Weeks: Implantation

The ball of rapidly dividing cells, called a blastocyst, implants in the uterus. 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 six and seven weeks, 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

From around week 9, your little one, now known as a fetus, may start moving around. 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 lose their webbing and continue to grow longer. It won't be long until you're able to count them!

10 or 11 Weeks: The Sound of Your Baby's Heart

From around weeks 10 or 11 your little one's heart may be beating loud enough to be heard with a Doppler ultrasound, which your healthcare provider may perform at your next appointment during the first trimester.

What's Going On in the First Trimester

Are you experiencing any of the typical first trimester pregnancy symptoms, but 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.

Some moms-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 triggers more intense mood swings than you may be used to. You may also 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. You can stay up-to-date with all these exciting changes by downloading our Pregnancy Guide. It's packed with information that will help you get through this trimester, and the next two as well.

This trimester, usually between 11 and 13 weeks, your healthcare provider may offer to schedule an optional screening test and will also explain the test in more detail. A first trimester screening test, which typically includes a blood test and an ultrasound scan, checks for Down syndrome and other abnormalities or birth defects. The blood test monitors the levels of certain substances in the blood, and the ultrasound checks for any extra fluid at the back of the neck of the fetus. It's important to note that a first trimester screening doesn't diagnose any particular conditions; rather, it evaluates the possible risk of various conditions. If your healthcare provider observes certain risk factors, you may choose to have more thorough, diagnostic tests done.

First Trimester Symptoms

The symptoms you experience in the first trimester might vary from week to week. Plus, the symptoms you experience during this pregnancy could differ from what you experienced in a previous pregnancy. In addition to symptoms like breast tenderness and fatigue, which might occur in early pregnancy, here are some of the most common symptoms during this trimester:

  • Implantation bleeding. After conception, as the fertilized egg implants in your uterus, you may experience some light cramping and spotting early in the first trimester. Contact your healthcare provider if you have any questions or concerns.

  • Nausea. The queasiness (and sometimes vomiting) known as morning sickness usually appears in the first trimester, although, contrary to its name, it doesn't strike only in the mornings! Try to think of morning sickness as a reassuring reminder that you are expecting a baby. Some simple strategies, like sucking on a lemon wedge or drinking ginger tea, might help the nausea subside.

  • 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.

  • Pregnancy "glow." Thanks to the increased amount of blood in the body and pregnancy hormones, your skin may look more rosy and even shinier in the first trimester.

  • Hormonal acne. An increase in oil production triggered by hormones can clog pores and lead to acne in some moms-to-be.

  • Cravings. Many women have hankerings for unusual foods when they're pregnant, and these are usually nothing to worry about. If you start to crave any non-food items like clay, ice, or laundry detergent, talk to your healthcare provider right away.

FAQs at a Glance

Can I have caffeine while pregnant? Because not much is known about the effects of caffeine on growing babies, experts recommend that you limit your intake to about 200 milligrams of caffeine per day. This is the amount in a 12-ounce cup of coffee at most.

Do I need prenatal vitamins? A healthy diet is a great start, but prenatal vitamins containing iron and folic acid can help support the growth and development of your baby and can help prevent birth defects. Check in with your healthcare provider, who can advise whether a prenatal vitamin alone, or in combination with a supplement, is best for you.

Can I get a flu shot while pregnant? Yes, pregnant women are vulnerable to flu infections, and the shot is safe for you and your baby. But always check with your healthcare provider before getting one.

Checklist for This Trimester

  • Prepare for a wide range of emotions during your pregnancy. Remind yourself that it’s perfectly 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 healthcare provider about your feelings during this trimester, or at any other stage of pregnancy, and even beyond.

  • Eat a healthy, balanced diet to help with morning sickness and cravings. Your healthcare provider can give you more information about your calorie and nutritional needs during this time, and our pregnancy guide also contains more handy information about nutrition for you and your baby.

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

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