Morning sickness
Why nausea and vomiting happen in pregnancy, when they ease, what helps and when to call a doctor.
3 min read
First trimester
Week 4 of pregnancy
The embryo has settled in your womb and is the size of a poppy seed. For many women this is the week the period is late.
Your baby is the size of a poppy seed
- Length, head to bottom
- ≈ 1 mm
Your baby this week
- The embryo has embedded in the lining of the womb and is about 1 millimetre across.
- The amniotic sac forms, which will protect the baby, along with the yolk sac, which feeds it in the first weeks.
- The cells are dividing into layers that will later become the brain, heart, lungs and every other organ.
- The placenta begins to form; it will bring the baby oxygen and food.
Your body this week
- Your period does not come. Your body makes the hormone hCG, which a pregnancy test picks up.
- You may have light spotting as the embryo embeds, which is easy to mistake for a period.
- Some women already feel tired, have tender breasts or mild period-like cramps.
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Read more for this stage
Your first pregnancy appointments
When to see a doctor once you know you are pregnant, what happens at the first appointment and what the check-ups look like until the birth.
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Early signs of pregnancy
A missed period, tiredness, sore breasts and nausea: how to recognise the early signs, when to take a test and when to see a doctor.
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General information written by the mam.al editors. Every pregnancy is different and sizes are averages; it does not replace advice from your doctor or midwife. Sources include the NHS week-by-week guide to pregnancy. NHS. Contains public sector information licensed under the Open Government Licence v3.0.