3 Weeks Pregnant
Reviewed by Safi Allah Khan
Medically reviewed by: Safi Allah Khan · Written by the Momi team · Last updated 20 October 2026
Quick answer: At 3 weeks pregnant, there is no baby yet. Pregnancy is counted from the first day of your last period, so weeks 1 and 2 come before conception and week 3 is when fertilisation and implantation happen. You're at the very start of the first trimester, with 37 weeks to your due date.
| Week 3 at a glance | |
|---|---|
| Trimester | First |
| Month | 1 |
| Weeks to due date | 37 |
| This week | Fertilisation and implantation |
Your baby at 3 weeks
The fertilised egg divides again and again as it travels to the uterus. By the end of this week, the ball of cells (a blastocyst) begins to implant in the lining of the uterus and starts making the pregnancy hormone hCG.
Your body at 3 weeks pregnant
Some people get light spotting or mild cramps around implantation. It is usually lighter than a period. Most people don't feel any different yet.
Things to do this week
- Wait to test. Home tests are most reliable from the day your period is due.
- Keep up folic acid and a balanced diet.
- Avoid alcohol if you might be pregnant.
When to call your doctor or midwife
Contact your care team straight away if:
- you have severe pain low on one side of your belly, or pain in the tip of your shoulder, after a positive test or a late period
- you have bleeding that is heavier than spotting
- you get a positive test and take regular prescribed medicine (ask before stopping anything)
If something feels wrong, trust that feeling and call. In an emergency, call your local emergency number.
Track week 3 in Momi
Once you have a positive test, set up Momi with your last period date to see which week you are in. Momi follows your pregnancy week by week with your baby's size and development, and keeps your diary, bump photos, appointments, kick counts and contractions in one place.
Download Momi free on the App Store or Google Play. Free with ads; optional Premium.
Keep reading
← 2 weeks pregnant · All weeks · 4 weeks pregnant →
Sources
- ACOG Committee Opinion No. 700: Methods for Estimating the Due Date
- NHS: Signs and symptoms of pregnancy
- NHS Best Start in Life: Week-by-week guide to pregnancy
Medical disclaimer: Momi and this website provide general information, not medical advice. Always talk to your doctor or midwife; in an emergency call your local emergency number.
FAQ
Am I really pregnant at 3 weeks?
Not yet in the everyday sense. Doctors date pregnancy from the first day of your last period, so the first two weeks happen before conception and week 3 is when the fertilised egg implants. If you conceive this cycle, these weeks still count toward your 40.
How many months is 3 weeks pregnant?
3 weeks pregnant is in the first month of pregnancy and the first trimester. Months don't divide evenly into 40 weeks, so different sources may label the month slightly differently.
Related guides
Track this in Momi
Momi is a free pregnancy tracker app for iPhone and Android that follows pregnancy week by week, estimates the due date, and keeps a pregnancy journal, weight log, kick counter and contraction timer in one place.
