Healthy pregnancy: your first trimester guide
Understand the key milestones of prenatal development, as well as the aches, weight gain, morning sickness, and other changes you may experience along the way.
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During pregnancy, many changes are happening to your body. There may also be new words to learn.
When tracking your pregnancy, it helps to understand the term “gestational age.” This is the term used to describe the progress of a pregnancy. Week 1 of gestational age starts from the first day of your last menstrual cycle, before you are actually pregnant and when your body is preparing for pregnancy.
We’ve compiled essential information about the key milestones of the first trimester (the first three months of pregnancy), as well as what you may experience, including morning sickness to the first movements of the fetus.
It’s important to know that if you have a high-risk pregnancy—whether because you are older than 35, have a history of preeclampsia, or have conditions such as diabetes, obesity, or high blood pressure—you may need to see a maternal-fetal medicine (MFM) specialist in addition to your regular healthcare provider (HCP).
Sources: National Library of Medicine. MedlinePlus. Gestational age. Review date December 10 + 14
- National Library of Medicine. MedlinePlus. Gestational age. Review date December 10, 2021.
- National Library of Medicine. MedlinePlus. Fetal development. Review date July 13, 2021.
- Mayo Clinic. Pregnancy week by week. High-risk pregnancy: Know what to expect. January 18, 2022.
- Cleveland Clinic. Fetal Development: Stages of Growth. Last reviewed April 16, 2020.
- Public Health England. Week-by-week guide to pregnancy. Accessed November 16, 2022.
- Mayo Clinic. Pregnancy week by week. Fetal development: The 1st trimester. June 3, 2022.
- American College of Obstetricians and Gynecologists. The Rh Factor: How It Can Affect Your Pregnancy. Last updated: June 2022.
- American College of Obstetricians and Gynecologists. Maternal Immunization. Committee Opinion. Number 741. June 2018.
- American College of Obstetricians and Gynecologists. ACOG and SMFM Recommend COVID-19 Vaccination for Pregnant Individuals. July 30, 2021.
- American College of Obstetricians and Gynecologists. Maternal Respiratory Syncytial Virus Vaccination. September 2023.
- Centers for Disease Control and Prevention. Respiratory Syncytial Virus Infection (RSV). Immunizations to Protect Infants. August 30, 2024.
- BabyCenter. Pregnancy Week by Week. Accessed November 16, 2022.
- Mayo Clinic. Pregnancy week by week. Fetal development: The 2nd trimester. June 3, 2022.
- Parents. How Big Is My Baby This Week? Here’s a Baby Fruit Size Chart. Updated on May 17, 2022.
- Centers for Disease Control and Prevention. Weight Gain During Pregnancy. Page last reviewed: June 13, 2022.
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