First Trimester Pregnancy Guide
The first trimester spans weeks 1–13 and is a period of remarkable transformation. From a single cell to a fully formed fetus with all major organs, this is when the most critical development occurs.
What Happens in the First Trimester?
The first trimester is arguably the most dramatic period in pregnancy. During these 13 weeks, a fertilized egg becomes a fully formed fetus complete with a beating heart, developing brain, limbs, and all major organ systems. By the end of week 13, your baby — now officially called a fetus — is about 7–8 cm long and weighs about 23 grams.
For the mother, the first trimester brings some of the most intense pregnancy symptoms. Rising hCG (human chorionic gonadotropin) levels — the “pregnancy hormone” — cause nausea, fatigue, and breast changes. Progesterone levels also surge, supporting the pregnancy and causing many of the early symptoms you feel.
Week by Week: First Trimester
Essential First Trimester Tips
400–800mcg folic acid daily reduces neural tube defect risk by 70%. Start before conception if possible.
Schedule your first prenatal appointment at 8–10 weeks. Earlier if you have risk factors.
Eat small, frequent meals; try ginger tea; take B6 (100mg/day). Avoid strong smells. Rest when possible.
No alcohol, no smoking, limit caffeine to <200mg/day, avoid raw meat and unpasteurized foods.
Frequently Asked Questions
Common questions answered by our medical team