Our Baby Journey4 weeks pregnant
4 weeks pregnant is about 1 month. It falls in the first month of pregnancy. You are in week 4 of 40, in the first trimester. Here is what is happening with your baby and your body this week.
Your baby is about the size of a poppy seed.
Length: about 1 mm (0.04 in) · Weight: less than 1 g
Your baby at 4 weeks
The embryo has implanted in the uterine wall. The placenta and the amniotic sac are starting to form.
Implantation is finishing this week, and the cells that will become your baby are settling deep into the lining of your uterus. The inner group of cells organizes into a flat disc made of two layers. From this tiny disc, every part of your baby's body will eventually develop.
Two important support structures are forming alongside it. The amniotic cavity, which will become the fluid-filled sac that cushions your baby, appears on one side, and the yolk sac appears on the other. The yolk sac provides early nourishment and makes the first blood cells until the placenta is ready to take over.
Meanwhile, the outer cells grow finger-like projections into your uterine lining. These are the beginnings of the placenta, which will connect with your blood supply to deliver oxygen and nutrients. They also release hCG, which tells your body to keep producing progesterone and not to have a period.
Your body at 4 weeks
Your period is due. A home pregnancy test may now show positive. Breast tenderness and tiredness can begin.
The main sign this week is a missed period. Because hCG levels rise quickly in early pregnancy, a home test is often positive around the day your period is due. Rising progesterone can make you feel unusually sleepy and can make your breasts feel sore, heavy, or tingly. Some people have light cramping or spotting as implantation completes. Others feel no different at all, which is just as normal. If you have not been taking folic acid yet, start it now.
Your belly at week 4
In month 1 (weeks 1–4) there is no visible change to your belly, and your uterus has barely changed size.
Belly size and shape vary a lot depending on your build, whether this is your first pregnancy, your baby's position and the amount of amniotic fluid. At checkups your doctor or midwife may measure your fundal height to track your baby's growth, and may arrange an ultrasound if the measurement is quite different from what they expect.
Symptoms at 4 weeks pregnant
- Missed period
- Sore, tingly, or heavy breasts
- Tiredness
- Mild cramping
- Light spotting
- Feeling of needing to urinate more often
Checkups around week 4
Once you have a positive test, contact your doctor or midwife to arrange your first prenatal appointment. The first visit is often scheduled between about 8 and 10 weeks, but timing varies by country and provider. Contact them sooner if you have a medical condition, take regular medication, or have had a previous ectopic pregnancy or miscarriage.
Tips for week 4
- Take a home pregnancy test if your period is late.
- Book your first prenatal appointment.
- Rest when you feel tired — early fatigue is very common.
Common symptoms in the first trimester
The first trimester runs from week 1 to week 13. It is when your baby's major organs, spine and heart form, and when many people feel the most tired and nauseous. Not everyone has every symptom, and it is normal for symptoms to come and go. Common ones include:
- Nausea and vomiting (morning sickness), which can happen at any time of day
- Tiredness and needing more sleep
- Tender, swollen breasts
- Needing to urinate more often
- Food aversions or cravings and a metallic taste
- Mood swings
- Light spotting around implantation
Read the full first trimester guide.
When to call your doctor or midwife
Contact your healthcare provider or maternity unit straight away, or get emergency care, if you have:
- Vaginal bleeding
- Severe or persistent abdominal pain or cramping
- A severe headache, blurred vision, or sudden swelling of your face, hands or feet
- A fever of 38°C (100.4°F) or higher
- Fluid leaking from your vagina
- Severe vomiting where you cannot keep fluids down
- Your baby moving less than usual or a change in their pattern of movements (later in pregnancy)
- Regular contractions before 37 weeks
- Pain or burning when you urinate
- Feeling very low, anxious, or having thoughts of harming yourself
Have a question about week 4?
Ask our AI pregnancy assistant about symptoms, nutrition, scans or anything else on your mind this week.
Frequently asked questions
How big is my baby at 4 weeks pregnant?
At 4 weeks pregnant, your baby is about the size of a poppy seed. That is about 1 mm (0.04 in), weighing less than 1 g.
How big is my belly at week 4 of pregnancy?
In month 1 (weeks 1–4) there is no visible change to your belly, and your uterus has barely changed size. Bump size, shape and when you start to show vary a lot from person to person.
Can I take a pregnancy test at 4 weeks?
Yes. Week 4 is when your period would normally be due, and many home tests can detect hCG by then. Use your first morning urine if possible, since it is the most concentrated. If the result is negative but your period still has not come, test again in a few days, as levels may still be rising.
Why is my pregnancy test line so faint?
A faint line usually still means a positive result, because the test has detected hCG. Early on, hCG levels are low and rise over the following days, so the line often gets darker if you test again in two or three days. If you have pain, heavy bleeding, or concerns, contact your doctor or midwife.
Is cramping normal at 4 weeks pregnant?
Mild cramping, similar to period cramps, is common in early pregnancy as the embryo implants and your uterus begins to change. Seek urgent medical advice if cramping is severe, one-sided, or comes with heavy bleeding, shoulder-tip pain, dizziness, or fainting, as these can be signs of an ectopic pregnancy.
What trimester is 4 weeks pregnant?
Week 4 is in the first trimester, which covers weeks 1 to 13.
How many months is 4 weeks pregnant?
4 weeks pregnant is about 1 month. It falls in the first month of pregnancy. The first month covers weeks 1 to 4. Pregnancy is about 40 weeks, or roughly 9 months, counted from the first day of your last period.
This page is general educational information and is not a substitute for advice from your doctor or midwife. Every pregnancy is different, and baby sizes are approximate averages. Last updated 2026-11-07. See our medical disclaimer.