PregnancyTrimestersFirst Trimester of Pregnancy

First Trimester of Pregnancy

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Few of life’s moments are as exciting and nerve-wracking as seeing a positive home pregnancy test. You may be over the moon or you may be feeling mixed emotions – fear, joy, apprehension, surprise (and maybe some nausea!). Take a deep breath and know that you’re not alone. Read on for our guide of what to expect in the first trimester of your pregnancy including signs and symptoms in the first 13 weeks of your pregnancy.

What to Expect in Your First Trimester of Pregnancy

Pregnancy is 40 weeks in total and is split up into three trimesters. The first trimester ranges from weeks one through 13.

How is My Due Date Calculated?

The 40-week countdown begins on the first day of your most recent menstrual period, which is usually about two weeks prior to ovulation and conception. That’s right—two bonus weeks of pregnancy have technically already lapsed by the time you conceive!

During your first ultrasound, your doctor will take measurements to confirm how far along you are. If you have irregular periods or are unsure of dates, your doctor will assign a due date based on these measurements.

Take a look at our due date calculator here.

Symptoms in the First Trimester

For some, the first trimester is the hardest of them all due to unpleasant symptoms, while others may barely feel pregnant. first trimester symptoms can include:

  • Nausea with or without vomiting
  • Food aversions and/or cravings
  • Heartburn and indigestion
  • Tender and/or enlarged breasts
  • Frequent urination
  • Constipation
  • Fatigue

There are several home remedies for these ailments.

Nausea and Vomiting

For the most common symptom, nausea and vomiting, you can try eating small meals often versus three large meals, using aroma therapy (lemon and ginger are great!), or wearing motion sickness bands. If these conservative measures aren’t doing the trick, talk with your doctor about prescription medication options.

Morning Sickness: Did you know?

The term ‘morning sickness’ is a bit of a misnomer – many women experience nausea all day long, and for some, it’s actually worse in the evenings. Try taking your prenatal vitamin before bed rather than in the morning, because some experts believe nausea is caused by the iron in the vitamin, which many women take first thing in the morning.

Try to get as much rest as possible and stay hydrated (easier said than done if you are working and/or have other little ones to take care of!).

Keep in mind: there is a wide range of what’s considered “normal” in pregnancy. If you are not feeling these symptoms, don’t stress, and consider yourself one of the lucky ones!

Your Baby in the First Trimester

From weeks one through 13, your baby will grow exponentially. They will be considered an embryo until about week 10 when they will graduate to a fetus.

During the first trimester, your baby will go from being a tiny speck the size of a poppy seed to almost three inches in length, about the size of a lemon (but much sweeter!).

They will form bones, fingernails, toenails, hair, vocal cords, and all necessary organs. They will also go from having a tadpole-like shape to looking a lot more like a baby.

Your Body in the First Trimester

In the first trimester, your uterus will start to grow to house your baby, the placenta, and amniotic fluid. Unless you’re carrying twins, it will grow to be about the size of a grapefruit in this trimester.

Depending on many factors, you may or may not start to “show” quite yet. Women who have had prior pregnancies tend to show on the earlier side, whereas those who are carrying a baby for the first time will take longer.

During this first part of pregnancy, your body is growing a whole new organ to accommodate your baby. By the end of the 1st trimester, the placenta will provide nutrients and oxygen via the umbilical cord until birth.

Doctor’s Visits

While many women find out they are pregnant soon after their missed period (when baby is only about five weeks of gestational age), many prenatal care providers don’t schedule the first visit until you are about 10 weeks along. If you have certain risk factors, have gone through IVF, or have a history of miscarriage, your doctor may want you to come in for a Viability Check around six or seven weeks.

At the first visit, you can expect to have an 10 week ultrasound. Because the baby is still so tiny, the ultrasound will likely be done transvaginally, which means your provider will insert a long, thin probe called a transducer into your vaginal cavity. You’ll be able to see a sonogram, or picture, of your baby on a screen.

Besides hearing your baby’s heartbeat for the first time (music to your ears!), you can expect to go over guidelines for nutrition, medication, exercise, etc. during pregnancy. You should have the opportunity to ask as many questions as you’d like.

Your doctor will also likely want to run some tests. It is common to get a pap smear, STI test, as well as bloodwork during this appointment. Additionally, most offices offer genetic screening for chromosomal abnormalities such as the MaterniT® 21 Test or Prequel® Prenatal Screen. You can also find out the baby’s sex this way (if desired).

Lastly, your doctor will recommend that you are up to date on immunizations, specifically the Influenza and Covid-19 vaccines. Both are considered safe for both you and your baby during pregnancy and will help protect you from severe illness (it’s especially important in the first trimester to avoid a high fever).

After the first visit, the next routine visit will probably not be until around week 16 of pregnancy.

Feeling Nervous?

It’s very common for women to feel anxiety during the first trimester, especially if they have experienced a miscarriage in the past. Be sure to lean on your partner, family, and friends and perform as much self-care as possible during this time.

It’s a difficult reality that about one in four pregnancies end in miscarriage, and most are caused by a chromosomal abnormality that results in a non-viable pregnancy. In other words, it’s out of your control. Most miscarriages will happen in the first trimester, and the risk drops about 10% each week.

If a miscarriage does happen, talk to your provider to decide when to start trying again, and don’t be afraid to seek the support of a therapist or support group.


When does the first trimester start?

The first trimester runs from week 1 to week 13.

How many weeks long is the first trimester?

This first trimester lasts for 13 weeks.

What is the Difference Between a Fetus and Embryo?

From weeks one through 13, your baby will grow exponentially. They will be considered an embryo until about week 10 when they will graduate to a fetus.

In this series

First Trimester: This guide.

Second Trimester: Read our guide to the second trimester of your pregnancy.

Third Trimester: Read our guide to the third trimester of your pregnancy.

Routine blood tests during pregnancy: Our guide to the blood tests you’ll be recommended during pregnancy

Written by

Abigail Purcell, RN
Abigail Purcell, RN
Abigail is one of our expert writers and is a BSN, RN (Registered Nurse) with a wide range of experience. She has worked in Public Health, Medical-Surgical nursing, and, most recently, Paediatrics and Women’s Health. Her true passion is serving mothers and families by helping them navigate their healthcare. As a nurse writer, Abby enjoys being able to empower patients on a larger scale, using evidence-based information that is easy to access and understand.


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