Baby is the size of
2mm
Size
2mm
Length
Baby Development
Your baby is now officially an embryo, about the size of a poppy seed. The blastocyst has fully implanted in your uterine wall and is beginning to form two distinct layers of cells — one will become the embryo and the other the placenta.
The amniotic sac and fluid are forming to cushion your baby. The yolk sac is producing blood cells until the placenta takes over. This is when a home pregnancy test may first show positive.
Your Body This Week
During week 4, you may be experiencing some of the classic first-trimester symptoms. Morning sickness (nausea and vomiting) is common and can occur at any time of day. You might feel unusually tired as your body works hard to support your growing baby.
Breast tenderness and swelling are typical as your body prepares for breastfeeding. You may notice increased urination as your uterus grows and presses on your bladder. Some women experience food aversions or cravings, heightened sense of smell, and mood swings due to hormonal changes.
Light spotting can be normal, but always mention any bleeding to your healthcare provider. Constipation and bloating are also common as pregnancy hormones slow down digestion.
Tips for This Week
Take your prenatal vitamins: Folic acid is especially important in early pregnancy to help prevent neural tube defects. Take your prenatal vitamin daily, ideally with food to reduce nausea.
Stay hydrated: Drink at least 8-10 glasses of water daily. This helps with fatigue, constipation, and supports amniotic fluid production.
Eat small, frequent meals: Combat morning sickness by eating smaller meals more often throughout the day. Keep crackers by your bedside for early morning nausea.
Rest when you can: First-trimester fatigue is real and your body is working incredibly hard. Don't feel guilty about needing extra sleep or rest.
To Do This Week
- Take a home pregnancy test
- Start taking prenatal vitamins if not already
- Schedule your first prenatal appointment
Frequently Asked Questions
How big is my baby at 4 weeks?▾
At 4 weeks pregnant, your baby is growing rapidly. Check the baby stats section above for exact measurements and fun size comparisons.
What symptoms are normal at 4 weeks pregnant?▾
Common symptoms at 4 weeks include fatigue, nausea (especially in the first trimester), breast tenderness, and increased urination. Every pregnancy is different, so your experience may vary.
What should I avoid at 4 weeks pregnant?▾
Throughout pregnancy, avoid alcohol, smoking, raw or undercooked meats, high-mercury fish, and certain medications. Check our Is It Safe? tool for specific items.