Week 4 is usually the week a period is missed, which is how most pregnancies are first noticed. Nothing shows on the outside yet, and plenty of women feel no different at all. Pregnancy is dated from the first day of the last period, so week 4 falls roughly two weeks after conception rather than four.
Your body this week
Almost nothing is visible. The NHS notes that in a first pregnancy many women do not start to show until at least week 12, and that women who have been pregnant before sometimes show sooner because the muscles of the womb and belly have stretched already.
Inside, the pregnancy hormone human chorionic gonadotrophin is rising. It is the hormone home pregnancy tests look for, which is why a test can turn positive before there is anything to feel or see.
The dating question confuses almost everyone at this point. Counting from the last period is a convention, not a claim about when conception happened, and it is the reason a "4 weeks pregnant" result can arrive only days after a missed period. Work out where you are if the numbers do not seem to line up.
What you may notice
Possibly nothing. The NHS lists a missed period as often the first sign, alongside sore breasts, a metallic taste, tiredness, nausea at any time of day, a heightened sense of smell, needing to pee more often, new food likes and dislikes, and a milky white vaginal discharge.
Some women notice light spotting around now. Light spotting is common in early pregnancy, but the NHS advice is to tell a doctor or midwife about any bleeding in pregnancy rather than deciding for yourself what it is.
Cramping a little like period pain is also common. Severe pain, particularly on one side, is not something to wait out — see the red-flag box below.
If none of this is happening to you, that is not a warning sign. Symptoms in early pregnancy vary enormously from woman to woman and from pregnancy to pregnancy.
Your baby this week
Around week 4, an embryo is about 2mm long — roughly the size of a poppy seed, in the NHS's own illustration. Those figures describe averages across many pregnancies, not a measurement of any particular one.
At this stage the embryo sits inside an amniotic sac filled with cushioning fluid, attached to a small yolk sac that supplies everything it needs for now. The outer layer of cells will go on to become the placenta.
What care usually happens around now
Nothing is scheduled this week in most systems, but this is when many women make first contact. NHS guidance is to see a GP or refer yourself to a midwife as soon as you know, because the first full appointment — the booking appointment — usually happens between weeks 8 and 12 and takes about an hour.
Guidelines also recommend a folic acid supplement in early pregnancy, which is why the first conversation matters more than the first scan. Antenatal schedules differ between countries, so what is offered near you may not match a UK timeline.
This week's tip
Write down the first day of your last period, and keep it somewhere you will not lose it. Every date offered to you for the next nine months is calculated from it, and it is the single question you will be asked at every first appointment. If your cycles are irregular and you genuinely do not know, say so — a dating scan exists for exactly that reason.
When to see a doctor
Contact a midwife, GP or maternity service if you have any bleeding, if pain is severe or one-sided, or if you feel faint. Pregnancy warning signs covers the full list. If a positive test has not been confirmed yet, when to take a pregnancy test explains the timing.
Seek care now: Contact your local emergency services or go to your nearest emergency department if you have heavy bleeding, severe or one-sided tummy pain, pain in the tip of your shoulder, a severe headache with vision changes, sudden swelling of the face or hands, a fever, chest pain, trouble breathing, fainting, or a seizure. Femio cannot assess a pregnancy.
Frequently asked questions
Why am I 4 weeks pregnant if I only just conceived?
Because the count starts at the first day of your last period, about two weeks before conception. It is a shared convention so that everyone measures the same way.
I have no symptoms at all. Is that a problem?
No. Many women have no symptoms in week 4, and the absence of symptoms says nothing about how a pregnancy is going. Week 5 is when a lot of women first notice something.