Sizes are averages; from week 20 length is measured head to heel. Not sure which week you’re in? Calculate it.
Your baby at 4 weeks
The blastocyst has burrowed into the uterine lining (implantation). Its cells are now splitting into two jobs: some will become the placenta, the rest the embryo. The embryo arranges itself into three layers – ectoderm, mesoderm and endoderm – that will build every organ. The amniotic sac and yolk sac are forming.
Your body at 4 weeks
The developing placenta has started releasing hCG, the hormone that turns a pregnancy test positive. Your period is due – or just missed. A little light spotting around this time can be implantation bleeding.
Common symptoms this week
- Missed period
- Light spotting
- Tender breasts
- Mild cramps
Tips & to-do list
- Take a home pregnancy test with first-morning urine – see our test calculator.
- Continue folic acid.
- Calculate your due date and book your first antenatal appointment.
Check-ups and tests around this week
- First antenatal visit, pregnancy registration and routine blood & urine tests
Week 4 at a glance
| At 4 weeks | |
|---|---|
| Trimester | First trimester |
| Pregnancy month | Month 1 of 9 |
| Weeks to due date | 36 weeks |
| Days pregnant | 28–34 days |
| Progress | 10% of 40 weeks |
When to call your doctor
Contact your doctor or go to hospital straight away if you notice:
- Heavy vaginal bleeding or passing clots
- Severe or one-sided abdominal pain, shoulder-tip pain or fainting (possible ectopic pregnancy)
- Vomiting so severe you can’t keep fluids down
- Fever above 38 °C or burning urination
Questions about 4 weeks pregnant
How many months is 4 weeks pregnant?
4 weeks pregnant falls in month 1 of pregnancy, in the first trimester. For medical purposes, weeks and days are more precise than months.
How big is my baby at 4 weeks?
At 4 weeks your baby is about the size of a poppy seed (khus khus) – roughly ~1 mm long and weighing about —.
Is it normal to have no symptoms at 4 weeks?
Yes. Every pregnancy is different, and symptoms come and go. Feeling well is not a sign that something is wrong. If you have concerns, or notice any warning signs listed on this page, contact your doctor.
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Medical disclaimer: The results and information on this page are estimates for general education only. They are not a diagnosis and do not replace advice from your gynaecologist, obstetrician or midwife. If you have pain, bleeding, reduced baby movements or feel unwell, contact your doctor or call 108 immediately. Read the full disclaimer.