4 Weeks Pregnant: What to Expect This Week

Baby's Development at 4 Weeks

The fertilised egg implanted into the uterine wall just days ago, and already a remarkable amount is happening. The outer layer of cells is forming the placenta, your baby's lifeline for the next nine months, while the inner layer is becoming the embryo itself. The neural tube — the structure that will become the brain and spinal cord — has started to form, which is why folic acid is so critical at this stage. Two fluid-filled sacs, the amniotic sac and the yolk sac, are taking shape to protect and nourish your developing baby.

Your Body at 4 Weeks Pregnant

At four weeks many people feel little to nothing, while others notice a missed period, mild cramping, or light spotting from implantation. Breast tenderness and fatigue are among the earliest signs. Heightened smell and a subtle feeling of queasiness may begin to appear, though full morning sickness typically peaks a few weeks later.

Tips for Week 4

• Start a prenatal vitamin with at least 400 mcg of folic acid if you haven't already — the neural tube closes by week 6.
• Book your first prenatal appointment. Most OBs and midwives schedule the first visit between weeks 8–10.
• Avoid alcohol, raw fish, and high-mercury fish from now on.
• Take a photo of your belly each week — you'll treasure the progression later.

Frequently Asked Questions