Week 4 of pregnancy
Week 4 is early days: much of what happens now is too small to see, and you may be the only one who knows.
About the size of a poppy seed
| Size | About a poppy seed |
|---|---|
| Length | 0.08 in (0.2 cm), measured from head to bottom (crown to rump) [1] |
| Trimester | First trimester |
| Weeks to go | About 36 to your due date |
These are averages. Every baby grows at their own pace.
What is forming this week
The embryo is about 2 mm long. It sits in a sac of cushioning fluid and gets its food from a tiny yolk sac. [1]
How you may feel
You may have no symptoms at all yet. A missed period is often one of the first signs. [1]
Everyone's pregnancy is different. If something worries you, call your midwife or doctor.
One thing to do this week
Note the first day of your last period. Pregnancy is dated from that day. [1]
Questions you could bring to your next appointment
- When is my dating scan, and what will it check?
- Which medicines and supplements are fine to keep taking?
- Who do I call if I'm worried between appointments?
Questions
When is the first scan?
In England the NHS offers the first scan, often called the 12-week or dating scan, at 11 to 14 weeks. In the US the timing of the first ultrasound depends on your care team, so ask at your first appointment.
Why is pregnancy counted from my last period?
Weeks are counted from the first day of your last period. Pregnancy is assumed to start about 2 weeks after that, so week 4 is only around 2 weeks after conception.
Is my baby exactly this size?
Probably not exactly. The length is the average the NHS gives for this week. Your scan results are the ones that count, and your midwife or doctor is the person to ask about them.
Sources
- NHS: 4 weeks pregnant guide Checked October 30, 2026
- ACOG: How your fetus grows during pregnancy Checked October 30, 2026
- NHS: Ultrasound scans in pregnancy Checked October 30, 2026
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