8 weeks pregnant: when the embryo becomes a fetus
8 weeks pregnant is a stage at which, the NHS says, the baby is around 16 mm long, about the size of a raspberry, and the embryo becomes what it calls a fetus (NHS, 2026). This page sets out what the NHS, ACOG and the Office on Women’s Health say about week 8, and where their counting differs.
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Bleeding and cramping are common in early pregnancy and often do not mean miscarriage. The symptoms below, however, need to be assessed straight away.
- Soaking two or more sanitary pads per hour, or passing large clots
- Severe lower abdominal pain, especially on one side
- Pain at the tip of the shoulder
- Dizziness, fainting, or collapse
- Signs of shock — pale, clammy, rapid heartbeat, breathlessness
- Pain on opening bowels, or bladder or bowel changes
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How the sources describe development around 8 weeks
- Size and shape, NHS
- The NHS week 8 page in its week-by-week guide (NHS, 2026) gives the baby as around 16 mm long and compares it to a raspberry. It says the tiny head has started to uncurl a bit, the arms are longer than the legs because the upper part of the body grows faster, and the knees, ankles, thighs and toes have not developed yet.
- Development and size, Office on Women’s Health
- The Office on Women’s Health page on the stages of pregnancy (2025) says that at eight weeks all major organs and external body structures have begun to form, the heart beats with a regular rhythm, fingers and toes have begun to form, the eyes have moved forward on the face and eyelids have formed. It says that at the end of eight weeks the baby is a fetus, nearly 1 inch long, weighing less than one-eighth of an ounce.
- Development, ACOG
- ACOG’s list for weeks 1 to 8 includes the brain and spine beginning to form, cardiac tissue starting to develop and the inner ear beginning to develop (ACOG, How Your Fetus Grows During Pregnancy, 2024).
Weeks are counted from the first day of the last menstrual period, so about two weeks of the count come before conception (ACOG, How Your Fetus Grows During Pregnancy, 2024). This page covers 8 weeks 0 days to 8 weeks 6 days.
A normal pregnancy lasts about 40 weeks from the first day of the last menstrual period, so at 8 weeks about 32 weeks remain to the estimated due date (ACOG, How Your Fetus Grows During Pregnancy, 2024). Your own due date depends on your last period or a scan, not on the week alone.
Embryo or fetus: where the sources differ
The NHS says that around week 8 the embryo becomes a fetus, a word it says means offspring in Latin (NHS, 2026). The Office on Women’s Health also places the change at the end of eight weeks (Office on Women’s Health, 2025). ACOG counts from fertilization here: it says the developing baby is called an embryo for 8 weeks after fertilization and a fetus from 9 weeks after fertilization until birth (ACOG, 2024). ACOG also says that about two weeks of the pregnancy count come before conception, so by that arithmetic its change falls about two weeks later than the NHS’s, around week 10 of the pregnancy count. This page gives each figure as its source states it.
Your body at 8 weeks, as the NHS describes it
The NHS says the placenta is getting ready to provide nutrients and oxygen and take away waste, and that it is sprouting little branches that will let it attach to the wall of the womb. It says you might be feeling bloated and have slightly swollen breasts, that it will probably be a few more weeks before you start looking pregnant, and that as the expanding womb pushes on the bladder you may need to pee more often (NHS, 2026).
The NHS also says there may be times when you feel anxious and stressed, that sharing worries is important, and that a good start is to talk to your midwife or doctor (NHS, 2026).
Work out which week you are in
The Pregnancy week calculator takes your last period, conception date, scan or IVF transfer and shows how many weeks and days pregnant you are today.
Sources
- NHS Best Start in Life. Week 8 of pregnancy (week-by-week guide to pregnancy). nhs.uk, 2026.
- American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy (FAQ156). ACOG, 2024.
- Office on Women's Health, US Department of Health and Human Services. Stages of pregnancy. womenshealth.gov, 2025.
Frequently asked questions
When does an embryo become a fetus?
It depends on how the weeks are counted. The NHS says around week 8 of pregnancy (NHS, 2026). ACOG says a fetus is what the baby is called from 9 weeks after fertilization (ACOG, 2024), which is later in the pregnancy count because about two weeks are counted before conception.
How big is the baby at 8 weeks pregnant?
The NHS says around 16 mm long, about the size of a raspberry (NHS, 2026). The Office on Women’s Health says nearly 1 inch long and less than one-eighth of an ounce at the end of eight weeks (Office on Women’s Health, 2025). The two figures are given by different bodies and this page does not convert between them.