4 Weeks Pregnant
At week 4, the blastocyst has successfully implanted into your uterine wall and is now technically an embryo. It's about the size of a poppy seed, but incredible things are happening: it's splitting into two layers, one that will become the baby and another that will form the placenta. This is the moment when the neural tube, which will become the brain and spine, begins to form.
Baby's Development This Week
At week 4, the blastocyst has successfully implanted into your uterine wall and is now technically an embryo. It's about the size of a poppy seed, but incredible things are happening: it's splitting into two layers, one that will become the baby and another that will form the placenta. This is the moment when the neural tube, which will become the brain and spine, begins to form.
- The embryo is now about the size of a poppy seed.
- The neural tube (brain and spinal cord) begins forming.
- The embryo splits into three layers: ectoderm, mesoderm, and endoderm.
- The primitive heart tube starts to form.
- The amniotic sac and yolk sac are developing.
Your Symptoms at Week 4
You might notice a missed period this week, which is often the first big clue of pregnancy. Some women experience 'implantation bleeding'—light spotting that can be mistaken for a period—as well as early signs like bloating and breast tenderness as your pregnancy hormones, like hCG, begin to rise rapidly.
Take a home pregnancy test. (moderate)
Wear a supportive, comfortable bra. (mild)
Rest when possible and maintain good sleep hygiene. (moderate)
Eat small, frequent meals and stay hydrated. (mild)
When to Call Your Doctor
- Heavy bleeding or passing clots
- Severe abdominal or pelvic pain
- Persistent vomiting preventing you from keeping food down
- Fever over 100.4°F (38°C)
Week 4 Checklist
- ✓Take a home pregnancy test (essential)
- ✓Schedule your first prenatal appointment (essential)
- ✓Continue prenatal vitamins with folic acid (essential)
- ✓Avoid raw fish, deli meats, and unpasteurized cheese (essential)
- ✓Limit caffeine to under 200mg per day (recommended)