4 weeks pregnant
At 4 weeks you are in the first trimester, and your baby measures about 1 mm from crown to rump, about the size of a poppy seed. A home pregnancy test turns positive around now, and the first step in the Australian public system is a GP visit to confirm the pregnancy and start the referral to a public hospital.
Averages from standard growth tables; your scan gives your baby's own numbers.
Your baby at 4 weeks
The embryo has implanted and the placenta and amniotic sac are forming. A disc of cells a few millimetres across, with the yolk sac that feeds it until the placenta takes over.
How you might feel
Many people feel nothing yet; others notice tender breasts, tiredness or light spotting around the time a period was due.
A home test turns positive about now. Start folic acid and iodine if you have not already, stop alcohol and book a GP.
Call your maternity unit or GP today for bleeding, severe pain, or if you cannot keep fluids down. 13 HEALTH (13 43 25 84) in Queensland; 000 in an emergency.
What's due this week in Australia
See your GP to confirm the pregnancy
Confirm with a urine or blood test, agree your dates, review any medicines and health conditions, and start (or keep taking) a pregnancy multivitamin with 400 µg folic acid and 150 µg iodine.
Coming up: Choose your public maternity care model and get booked in
All of these are free with a Medicare card.
Coming up: First antenatal visit and booking blood tests
Blood pressure, height and weight.
Checklist for the week
Ticks save on this device. Create a free account to keep them on any phone.
Questions about 4 weeks
How many months is 4 weeks pregnant?
About one month. Pregnancy is counted from the first day of your last period, so at 4 weeks the embryo is only about two weeks old.
What trimester is 4 weeks?
Week 4 is in the first trimester. In the Australian guidelines Hello Bub follows, the first trimester runs to 13 weeks, the second from 14 to 27 and the third from 28 weeks.
Is 4 weeks too early to see a GP?
No. A GP can confirm the pregnancy with a urine or blood test, check the medicines you take and start the referral to a public hospital. In Queensland you can also refer yourself to a public maternity service online.
Written by the Hello Bub team; medical schedule follows the Australian Pregnancy Care Guidelines; last reviewed 3 November 2026.