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4 Weeks Pregnant: Your Baby, Your Body and What to Do
The ball of cells settles into the womb lining, and a missed period may be your first sign.
Before you use this guide: Pregnancy weeks are counted from the first day of your last period. Sizes are rough averages, and healthy babies vary. This is general information, not an individual medical assessment, so please confirm personal health decisions with your doctor or midwife.
How your baby is growing
This week the ball of cells reaches the womb and burrows into its lining. This is called implantation and usually happens 6 to 10 days after ovulation. The cells begin to separate into two groups: one will form the embryo, and the other will form the placenta and the sac that protects your baby.
The placenta starts to make the hormone hCG, which tells your body to keep the womb lining and stop your period. It is the hormone that pregnancy tests detect.
How you may be feeling
Your period may be due or just late, and a home test can now be positive. Some people have a little light spotting at implantation. Early signs such as tiredness, tender breasts, needing to pass urine more often and a metallic taste can begin, though many people feel nothing yet.
Your to-do list for week 4
- Take a pregnancy test if your period is late. If it is negative but your period still does not arrive, test again in a few days.
- Take folic acid every day until week 12.
- Avoid alcohol and smoking, and keep caffeine under about 200 mg a day, roughly two mugs of instant coffee.
- Tell your doctor or midwife you are pregnant so you can book your first appointment. In some places you can refer yourself.
When to ask for help
Light spotting can be harmless, but contact your doctor or midwife if bleeding is heavy like a period or comes with severe pain on one side of your tummy, shoulder-tip pain, dizziness or fainting. These can be signs of an ectopic pregnancy, which needs urgent care.
For heavy bleeding, severe pain, fluid leaking, a severe headache with vision changes, or a baby who is moving less than usual, do not wait for your next appointment. Contact your midwife, doctor or maternity unit straight away. Our guide to pregnancy warning signs has more detail.
Not sure which week you are in? Use the due-date calculator to estimate your due date and current week.
Useful at this stage: conception date calculator and pregnancy test calculator.
Trusted resources to read next
These public health resources provide additional information. Guidance can vary by country, so prioritise advice from your own care team and local health service.
- NHS: Pregnancy — Pregnancy care, common symptoms, screening and complications.
- NHS: Week-by-week pregnancy guide — Pregnancy development and care by week.
This content is for general information only and is not medical advice. Every pregnancy and every baby is different. Always talk to your doctor, midwife or paediatrician about your own situation, and seek urgent care if you are worried.