Pregnancy Week by Week: What to Expect Each Trimester

Congratulations on your pregnancy! This guide will walk you through every stage of your incredible 40-week journey.

First Trimester (Weeks 1-12)

The first trimester is a time of rapid development, though you might not look pregnant yet.

Weeks 1-4: Conception & Implantation

Baby's Development:

• Fertilization occurs
• Cells divide rapidly
• Implantation in uterine wall (week 4)
• Placenta begins forming

Your Body:

• May miss period
• Possible light spotting (implantation)
• Breast tenderness begins
• Fatigue may start

Weeks 5-8: The Embryo Phase

Baby's Development:

• Heart begins beating (week 6)
• Brain and spinal cord forming
• Arm and leg buds appear
• Facial features starting
• Size: sesame seed to raspberry

Your Body:

• Morning sickness often begins
• Frequent urination
• Mood swings
• Food aversions or cravings
• Heightened sense of smell

Weeks 9-12: Becoming a Fetus

Baby's Development:

• All major organs formed
• Fingers and toes develop
• Bones begin hardening
• Reflexes starting
• Size: cherry to lime

Your Body:

• Belly may start showing (slightly)
• Morning sickness often peaks
• Energy may start returning
• Skin changes possible

Key Appointments:

• First prenatal visit
• Blood tests and screenings
• Possible first ultrasound
• Discuss genetic testing options

Second Trimester (Weeks 13-27)

Often called the "honeymoon phase" – many uncomfortable symptoms ease!

Weeks 13-16: Energy Returns

Baby's Development:

• Can make facial expressions
• Starts producing urine
• Can swallow amniotic fluid
• Sex organs developing
• Size: lemon to avocado

Your Body:

• Energy increases
• Morning sickness fading
• Appetite returns
• Visible baby bump
• May feel flutters (quickening)

Weeks 17-20: Movement!

Baby's Development:

• Can hear sounds
• Covered in vernix (protective coating)
• Unique fingerprints form
• Regular sleep-wake cycles
• Size: pear to banana

Your Body:

• Definitely showing now
• Feel baby movements (kicks!)
• Lower back pain may start
• Skin changes (line nigra, stretch marks)
• Increased appetite

Key Appointment:

• Anatomy scan (18-22 weeks)
• Can often learn the sex!
• Detailed check of organs

Weeks 21-24: Rapid Growth

Baby's Development:

• Eyes can open
• Hearing developed
• Practices breathing
• Responds to sounds
• Size: papaya to corn

Your Body:

• Braxton Hicks may start
• Swelling in hands/feet
• Round ligament pain
• Sleep may become difficult
• Skin pigmentation changes

Weeks 25-27: Approaching Viability

Baby's Development:

• Can respond to your voice
• Lungs developing surfactant
• Eyes can perceive light
• Regular movement patterns
• Size: rutabaga to lettuce

Your Body:

• Shortness of breath
• Heartburn common
• Leg cramps
• Frequent urination returns
• Baby's movements stronger

Third Trimester (Weeks 28-40)

The home stretch! Baby is getting ready for the outside world.

Weeks 28-31: Brain Development

Baby's Development:

• Brain growing rapidly
• Can see and hear
• REM sleep occurring
• Gaining weight quickly
• Size: eggplant to coconut

Your Body:

• Belly button may pop out
• Difficulty sleeping
• Braxton Hicks more frequent
• Increased fatigue
• Nest instinct may begin

Key Appointments:

• Visits every 2 weeks now
• Glucose screening (if not done)
• Check baby's position

Weeks 32-35: Almost Ready

Baby's Development:

• Immune system developing
• Lungs nearly mature
• Less room to move
• In head-down position (usually)
• Size: squash to honeydew

Your Body:

• Pelvic pressure increases
• Difficulty breathing
• Swelling more common
• Trouble getting comfortable
• "Lightening" may occur

Weeks 36-37: Full Term Soon

Baby's Development:

• Considered "early term" at 37 weeks
• Organs ready to function
• Fat layer complete
• Strong sucking reflex
• Size: romaine lettuce to winter melon

Your Body:

• Visits now weekly
• Cervix may start changing
• Loss of mucus plug possible
• Nesting in full swing
• Mix of excitement and anxiety

Weeks 38-40: Ready to Meet Baby!

Baby's Development:

• Fully developed
• Continuing to grow
• Positioned for birth
• Alert and responsive
• Size: pumpkin to watermelon (6-9+ lbs)

Your Body:

• Extreme nesting urge
• Cervix dilating/effacing
• Possible "bloody show"
• Water could break
• Contractions intensifying

Signs of Labor

Watch for these signs:

• Contractions: Regular, increasing intensity
• Water breaking: Gush or trickle of fluid
• Bloody show: Mucus with blood
• Back pain: Persistent lower back pain

Your Hospital Bag Checklist

For Baby:

• Going-home outfit
• Car seat (installed!)
• Blanket
• Diapers

For Mom:

• Comfortable clothes
• Toiletries
• Nursing bras
• Phone charger
• Snacks

Every pregnancy is unique. This guide provides general information – always consult your healthcare provider with questions or concerns!