The first trimester: what happens and what to do
The first three months bring the biggest changes and often the most questions. Here is what to expect and what to do.
Try the calculator: Pregnancy due date calculatorWhat the first trimester covers
The first trimester runs from the first day of your last period to the end of week 13. Because gestational age is counted from the last period, you are already counted as two weeks pregnant when conception happens, so the baby's own age is about two weeks less than the number you hear.
Use our pregnancy calculator to find your exact week and your expected due date.
How the baby develops
This is when the baby's organs begin to form. The brain and spine start to develop in the first weeks, which is why folic acid is advised before and in early pregnancy. By the end of the trimester the baby has the basic structures of the body, and the next months are mostly growth.
Common symptoms
Symptoms vary a lot between women. Some feel almost nothing, and others feel very unwell. These are common.
- Tiredness, often very strong
- Nausea, with or without vomiting, which usually begins before week 9 and eases for most women by about week 14
- Tender or heavier breasts
- Needing to pass urine more often
- Mood changes and tearfulness
- Dislike of certain smells and foods
Your first check-up
The World Health Organization advises a first contact with a health professional before week 12. Your doctor will usually confirm the due date, ask about your health history, and check things like your blood pressure and blood tests. An ultrasound in the first trimester is the most accurate way to date the pregnancy, and your doctor may change the due date if it differs by more than about a week from your last period.
- Bring the date of your last period and your usual cycle length
- List the medicines, vitamins and herbs you take
- Write down your questions, and your family health history
Healthy habits from the start
A few choices matter most in these early weeks.
- Take folic acid as your doctor advises: the CDC recommends 400 micrograms a day before and in early pregnancy
- Avoid alcohol: no amount is known to be safe in pregnancy
- Do not smoke and avoid smoke around you
- Choose pasteurized dairy and cook meat, chicken and eggs well, as in our nutrition guide
- Ask your doctor before taking any medicine or herbal product
- Rest when you can; early pregnancy tiredness is real
When to call the doctor
Contact your doctor or emergency services right away for any of these.
- Vaginal bleeding
- Severe belly pain that does not go away
- Vomiting so severe that you cannot keep fluids down
- Fever of 38 degrees Celsius or higher
- Dizziness or fainting, or a severe headache
- Thoughts of harming yourself
This is general information, not a substitute for a doctor's advice.
Sources
- How Your Fetus Grows During PregnancyACOG (American College of Obstetricians and Gynecologists)
- New guidelines on antenatal care for a positive pregnancy experience (2016)WHO (World Health Organization)
- About Folic AcidCDC (US Centers for Disease Control and Prevention)
- Morning Sickness: Nausea and Vomiting of PregnancyACOG (American College of Obstetricians and Gynecologists)
- About Alcohol Use During PregnancyCDC (US Centers for Disease Control and Prevention)
- Urgent Maternal Warning Signs and Symptoms (Hear Her)CDC (US Centers for Disease Control and Prevention)
- Methods for Estimating the Due DateACOG (American College of Obstetricians and Gynecologists)