3 weeks pregnant
First trimester less than a month
At 3 weeks pregnant, the fertilized egg is a tiny ball of roughly 100 cells on its way to implant.
Baby this week
The fertilized egg — now called a zygote — is travelling down the fallopian tube, dividing rapidly from one cell into many. By the end of this week it arrives at the uterus as a blastocyst and begins burrowing into the uterine lining. This is implantation. You almost certainly don't know you're pregnant yet — hCG is not detectable by a home test this early.
Did you know? In just 4–5 days after fertilization, the single-celled zygote divides into roughly 100 cells forming the blastocyst. The inner cells will become the embryo; the outer cells will become the placenta.
What she may be feeling
- No pregnancy symptoms yet — hCG is not yet detectable
- Very possible: no symptoms at all
- Possible very light implantation spotting near end of week
- Possible mild implantation cramping near end of week
Tips for her this week
- Folic acid is critically important right now — continue prenatal vitamins daily without fail.
- Avoid any medications (even OTC) without checking with your doctor first.
- Cut out alcohol completely if you haven't already.
- Rest as much as possible — your body is doing enormous work invisibly.
For partners
- She almost certainly doesn't know she's pregnant yet — if you do, be extra gentle and attentive this week.
- Begin researching OB-GYNs or midwives in your area. Good ones book up fast.
- Limit your own alcohol intake — it's good modeling and easier on her if you're doing it together.
- Start educating yourself: folic acid is critical in the weeks surrounding conception.
Partner to-do list
- Research and list 3 OB-GYNs or midwives to call
- Reduce your own alcohol to model solidarity
- Read about early pregnancy and what to expect
- Book or plan the first prenatal appointment
This week together
- Confirm folic acid intake is happening daily
- Decide: OB or midwife?
- Start listing questions for your first appointment
When to call your doctor or midwife
Contact your care provider right away, or call emergency services, if she has:
- Heavy or bright red bleeding
- Severe one-sided pain
- Fever over 38°C / 100.4°F
Trusted guidance: NHS: Pregnancy · NHS: Pregnancy complications · ACOG: Pregnancy · Pregnancy Info: Your pregnancy
Common questions
How big is the baby at 3 weeks?
At 3 weeks pregnant, the fertilized egg is a tiny ball of roughly 100 cells on its way to implant. There's no measurable baby size yet.
How many months is 3 weeks pregnant?
3 weeks pregnant is less than a month, in the first trimester.
What can partners do at 3 weeks?
She almost certainly doesn't know she's pregnant yet — if you do, be extra gentle and attentive this week. Begin researching OB-GYNs or midwives in your area. Good ones book up fast.