First Trimester

Week 1

Baby is the size of a not yet conceived

• First day of last menstrual period — pregnancy dating starts here
• Ovulation and conception typically occur around week 2-3

Week 2

Baby is the size of a not yet conceived

• Ovulation typically occurs this week — your fertile window
• Sperm can survive 5 days; egg survives 12-24 hours after ovulation

Week 3

Baby is the size of a microscopic (pinhead)

• Fertilization occurs — sperm meets egg in fallopian tube
• Zygote divides: 2-cell → 4-cell → 8-cell → morula → blastocyst

Week 4

Baby is the size of a poppy seed

• Blastocyst implants in uterine lining — pregnancy established
• hCG begins rising; pregnancy test may turn positive late this week

Week 5

Baby is the size of a sesame seed

• Missed period — pregnancy test positive
• hCG rising rapidly; symptoms begin

Week 6

Baby is the size of a lentil

• Heart beating — often visible on ultrasound
• Neural tube closing; brain vesicles forming

Week 7

Baby is the size of a blueberry

• All essential organs have begun forming
• Heart fully formed with 4 chambers; beating 150-170 bpm

Week 8

Baby is the size of a raspberry

• Officially end of embryonic period — now a fetus
• Fingers/toes distinct (webbing gone); tail gone

Week 9

Baby is the size of a grape

• Heart fully formed with 4 chambers, valves, and beat 170+ bpm
• Embryo now officially a fetus — looks recognizably human

Week 10

Baby is the size of a strawberry

• Critical organ development complete — major defect risk drops
• Baby moves, swallows, and practices breathing

Week 11

Baby is the size of a fig

• Baby starts producing urine — amniotic fluid increases
• Diaphragm developing — baby practices 'breathing'

Week 12

Baby is the size of a lime

• Reflexes active: baby can open/close fingers, curl toes
• Pituitary gland producing hormones

Week 13

Baby is the size of a peapod

• Vocal cords present; baby can make subtle sounds
• Fingerprints fully developed and unique