First trimester

The first trimester spans weeks 1–13 — conception, implantation, and the formation of all major organ systems. Nausea and deep fatigue are common; folic acid and the first-trimester screen are the key milestones.

Months in this trimester

• 1 Months Pregnant ›
• 2 Months Pregnant ›
• 3 Months Pregnant ›

Key milestones

• Conception around week 3; implantation in week 4 — hCG begins to rise.
• Neural tube forms in weeks 5–6 — folic acid matters most here.
• Fetal heartbeat visible on ultrasound at week 6 (100–160 bpm).
• Nuchal translucency (NT) screening at weeks 11–13+6.
• By the end of week 13: ~7.4 cm, ~23 g. All major organ systems are in place.

Recommended prenatal care

• First prenatal visit at 6–8 weeks — confirm gestational sac and heartbeat.
• Initial blood panel — rubella, hepatitis B, HIV, blood type, CBC.
• NT ultrasound at 11–13+6 weeks.
• First-trimester combined screen (blood markers + NT).
• NIPT (cell-free DNA) is generally available from week 10.

Jump to trimester

• First trimester
• Second trimester
• Third trimester