First trimester: Physical changes and common discomforts

Fatigue, nausea, tender breasts ... Your belly hasn’t started growing yet, but already you can feel your body transforming. What changes and discomforts can you expect during the first trimester?

What physical changes occur during the first trimester?

Here are the main physical changes that occur during the first trimester (from conception to 14 weeks).

• You stop menstruating.
• Your uterus expands. This change will be noticeable in the second trimester, between the fourth and fifth months of pregnancy. If this is not your first pregnancy, however, you may start showing in your third month. Two months in, your uterus starts to grow 4 cm per month. At 12 weeks, it’s roughly the size of a grapefruit.
• Your breasts start to swell. They become heavier, firmer, and more sensitive. They can even be a little painful. Your nipples become firmer and darker. The areolas also become darker. Glands may become visible on the areolas. These glands produce an oil that helps keep the skin moisturized and protected during breastfeeding.
• The release of hormones lowers your blood pressure and slows down your digestive system. You may produce more saliva, sometimes excessively.
• You feel out of breath. This is perfectly normal! Your oxygen demand increases 15 to 20 percent during pregnancy. Your respiratory rate hasn’t increased. Rather, each breath pulls more oxygen into your lungs.
• You start to put on a bit of weight. However, some women may lose weight during this period due to nausea and vomiting.
• Your heart rate may increase slightly starting in the sixth week, as some of your blood flow is directed toward the embryo to meet its needs. Your heart rate will remain higher until the end of your pregnancy.

What are some common first-trimester pregnancy discomforts?

Pregnancy affects a woman’s entire body. The cardiovascular, digestive, respiratory, nervous, reproductive, and urinary systems are impacted. That means it’s normal to feel various aches and pains over the next few months.

Below is a list of the most common discomforts experienced in the first trimester. To learn more about a specific discomfort, click on its name and consult the fact sheet.

• Fatigue
• Frequent urge to urinate
• Headaches
• Heartburn
• Mood swings
• Nasal congestion
• Nausea and vomiting
• Pregnancy gingivitis
• Reflux
• Shortness of breath
• Vaginal discharge
• Vertigo and dizziness

Some over-the-counter medications can relieve certain pregnancy discomforts, but be sure to speak to your prenatal care provider or pharmacist before taking any.

If you’re concerned about any symptoms, make a note of them and discuss them with your prenatal care provider. Feel free to contact them between appointments. You can also call Info-Santé 811 if you have any concerns.

Things to keep in mind

• Certain physical changes develop in the early months of pregnancy.
• These changes affect the woman’s entire body.
• If you’re concerned about any of your symptoms, discuss them with your prenatal care provider.

Scientific review: Paméla Farman, M.Sc., nurse clinician and lecturer at the Université Laval faculty of nursing Research and copywriting:The Naître et grandir team Updated: May 2026

Photo : iStock.com/Perkus