Week 4: Implantation
You’re 4 weeks pregnant — about 36 weeks to go. Your baby is roughly the size of a poppy seed.
Size of
a poppy seed
Length
0.1 cm
0.0 in · crown to rump
Weight
—
Your baby this week
The blastocyst burrows into the uterine wall and splits into two parts: one becomes your baby, the other becomes the placenta. The amniotic sac is forming to cushion the months ahead.
Your body & how you might feel
Your body starts producing hCG — the hormone home pregnancy tests detect. A test may turn positive right around now, often with a faint line at first.
Common symptoms at week 4
- Light implantation spotting
- Tender breasts
- A missed period
This week’s tip: If you test too early and see a faint line, wait two days and test again — hCG roughly doubles every 48 hours.
A gentle reminder: This is an estimate, not medical advice. Dates and figures are general guidance — every pregnancy is different. Your healthcare provider’s assessment, especially from an early ultrasound, always takes priority. Always speak with your provider about your pregnancy.
Week 4 FAQs
How big is the baby at 4 weeks?
At 4 weeks pregnant, your baby is roughly the size of a poppy seed, about 0.1 cm (0.0 in) long. These are typical averages — every baby grows at its own pace.
How many months is 4 weeks pregnant?
4 weeks pregnant is less than 1 month, in the first trimester, with about 36 weeks to go until your due date.
What are common symptoms at 4 weeks?
Common experiences around week 4 include light implantation spotting, tender breasts, a missed period. Symptoms vary widely — contact your provider if anything worries you.