Week 4
Trimester 1Days 3+0 to 3+6
Baby is now the size of a poppy seed
Week 4 is often the week when pregnancy officially begins to establish itself. The tiny embryo may now implant into the lining of the uterus, creating a connection that will support its growth throughout pregnancy. Many people still have no symptoms at all, while others may begin noticing subtle changes. Some may even get their first positive pregnancy test this week.
Length
~1 mm
~0.4 in
Weight
< 1 g
2.2 lb
Development highlights
- check_circleThe blastocyst — a tiny ball of dividing cells — arrives in the uterus and begins to implant.
- check_circleOnce implantation occurs, the body starts producing the pregnancy hormone hCG.
- check_circleCells are organising into the structures that will become the baby, the placenta, and the amniotic sac.
This week's milestones
- check_circleImplantation into the uterine lining.
- check_circleFirst production of hCG — the hormone detected by pregnancy tests.
- check_circleThe foundations of the placenta begin to form.
Fun fact
At this stage, the embryo is smaller than a grain of rice, yet it already contains all the genetic information needed to grow into a baby.
Weekly checklist
- Continue taking prenatal vitamins.
- Stay hydrated.
- Eat nutritious meals.
- Get plenty of sleep.
- Avoid smoking and alcohol.
- Consider taking a pregnancy test if your period is due.
Frequently asked questions
Can I get a positive pregnancy test during Week 4?
Yes. Some people receive their first positive test during this week, especially toward the end when hCG levels have had more time to rise.
Is implantation bleeding normal?
Light spotting can occur during implantation, though many people never experience it. If bleeding is heavy or accompanied by severe pain, contact your healthcare provider.
Is it normal to have no symptoms?
Absolutely. Many healthy pregnancies begin without any noticeable symptoms. The absence of symptoms does not mean anything is wrong.
Why am I so tired?
Rising hormone levels, particularly progesterone, can begin causing fatigue very early in pregnancy — sometimes before a positive test.
Related tools
shopping_bagHelpful picks for Trimester 1
Browse all pregnancy products →Frida Mom Anti-Nausea Acupressure Bands
Drug-free acupressure wristbands for morning sickness relief — wear during the first trimester to ease nausea without medication.
Lokaheadr 1st Pregnancy Essentials Kit
Curated first-pregnancy essentials gift set for new moms-to-be — everything you need for a comfortable first trimester.
Momcozy Maternity Pregnancy Pillow
Full-length maternity pillow with removable sections for bump support, back relief, and comfortable side sleeping.
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Medical information disclaimer
The content on this page is provided for general informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.
Always consult your GP, midwife, health visitor, paediatrician, or other qualified healthcare provider before making decisions about your health or your child's health and development. Never ignore or delay seeking professional advice because of something you have read on BabyScout. If you think there is a medical emergency, call 999 (UK) or your local emergency services immediately.