4 weeks pregnant
First trimester less than a month
At 4 weeks pregnant, your baby is about the size of a poppy seed.
Baby this week
The embryo is now about 2mm. The heart is beginning to form, and the foundations of the brain, spinal cord, and digestive system are taking shape.
Did you know? A home pregnancy test detects the hormone hCG, which doubles every 48–72 hours in early pregnancy — this is what makes tests more reliable each day.
What she may be feeling
- Missed period
- Breast tenderness
- Fatigue
- Light cramping (normal)
- Possible light spotting
- Nausea may be starting
- Frequent urination
- Bloating
Tips for her this week
- A positive test this week is common — home tests are reliable from day one of a missed period.
- Call your OB or midwife to book the first appointment (usually scheduled around week 8–10).
- Continue prenatal vitamins and avoid alcohol, raw fish, and deli meats.
- Rest and don't stress — mild cramping and spotting can be normal at this stage.
For partners
- She may have just gotten a positive test — let that sink in together and be fully present.
- Be patient if she's emotional or anxious. Both are completely normal.
- Start planning when and how you'll book the first prenatal appointment.
- This is a good time to quietly start handling more around the house.
Partner to-do list
- Be fully present when she takes or shares the test result
- Call to book the first prenatal appointment
- Take over dinner and household tasks this week
- Tell her you're in this together — and mean it
This week together
- Book first prenatal appointment
- Decide who to tell and when
- Review health insurance prenatal benefits
- Celebrate quietly together
When to call your doctor or midwife
Contact your care provider right away, or call emergency services, if she has:
- Heavy bleeding more than a period
- Severe one-sided abdominal pain — possible ectopic
- Fever
- Passing tissue
Trusted guidance: NHS: Pregnancy · NHS: Pregnancy complications · ACOG: Pregnancy · Pregnancy Info: Your pregnancy
Common questions
How big is the baby at 4 weeks?
At 4 weeks pregnant, your baby is about the size of a poppy seed. The embryo is now about 2mm.
How many months is 4 weeks pregnant?
4 weeks pregnant is less than a month, in the first trimester.
What can partners do at 4 weeks?
She may have just gotten a positive test — let that sink in together and be fully present. Be patient if she's emotional or anxious. Both are completely normal.