First trimester
Pregnancy Week 3
Your baby is about the size of a pinhead.
Size
pinhead
Length
0.1 mm
Weight
< 0.001 g
Baby in week 3
Fertilization occurs. The single-cell zygote begins dividing as it travels down the fallopian tube. By end of week, a tiny ball of cells (blastocyst) implants in the uterine wall.
What you may notice this week
You likely won't notice anything yet. Some women notice very mild implantation spotting.
Tips for week 3
- Take folic acid daily (400–800 mcg)
- Avoid alcohol, smoking, and unnecessary medications
- Test in about 2 weeks
Tools that pair with this week
Due Date Calculator
Estimate your delivery date by last period or conception date. Naegele’s rule plus cycle adjustments.
Week Tracker
See exactly how many weeks and days pregnant you are, plus your trimester and key milestones.
Contraction Timer
Tap once to start, once to stop. Tracks duration, frequency, and pattern over time.
Ovulation Calculator
Find your fertile window based on your cycle length. Plan or avoid with confidence.
Baby Name Generator
Filter by origin, style, length, and starting letter. Boys, girls, and unisex.
Growth Percentile
Plot your baby’s weight, length, and head circumference against WHO percentile curves.