Week 10 is a milestone with a name change behind it: the embryo officially becomes a fetus. Organogenesis is essentially complete, and from here the work is growth rather than construction.
Your baby is about 33 mm and around 4 grams — the first week a weight is worth quoting at all.
The short answer: at 10 weeks the embryo becomes a fetus, marking the end of the organ-building period and the point at which the highest-risk window for medication and alcohol exposure largely closes. Fingers are fully separate, the tail has gone, and all 20 milk-tooth buds are in the gums. NIPT — a blood test screening for chromosomal conditions — becomes possible from about now.
Your baby this week
The webbing between the fingers has completely disappeared, leaving separate fingers and toes, and the hands can now be brought up towards the face. The tail is gone. In the gums, all 20 milk-tooth buds are laid down — the teeth that will not appear for another year after birth are already positioned.
The brain continues forming connections at an extraordinary rate, and the skull is still soft and thin over it. The liver, kidneys, intestines and brain are all in place and beginning to function, with the kidneys producing small amounts of urine.
Reaching the fetal stage matters practically as well as symbolically. Because the major structures are now built, the window in which an exposure could cause a structural malformation has largely passed. That is not a licence — alcohol has no safe level at any stage, and medication still needs checking — but it does mean an accidental exposure before you knew you were pregnant is now much less likely to have caused structural harm.
Your body this week
The uterus is now roughly the size of a large grapefruit. It is still below the pubic bone, so there is nothing to see from outside, but you may notice your usual trousers becoming tight at the waist — that is the uterus and bloating rather than the baby.
Veins across your chest and abdomen often become more visible, as the expanding blood volume shows through the skin. Hormone levels begin to stabilise around now, and some women notice their mood evening out even while the fatigue persists.
Nausea may still be severe — hCG does not fall until after about week 11 — so if this week feels no better than last, nothing has gone wrong.
Tests and appointments
Tests and scans around now: Non-invasive prenatal testing (NIPT) on a maternal blood sample becomes possible from about 10 weeks.
Exact timing varies by country and by your own care plan — your doctor or midwife will confirm the schedule that applies to you.
NIPT is the main new option this week. It is highly accurate as a screening test for Down syndrome and some other chromosomal conditions, and it carries no procedural risk because it only needs a blood sample from you. It does not replace the 11–14 week scan, which also measures nuchal translucency and confirms dates and viability.
This is also a good week to ask specifically about your thyroid. Your baby's thyroid is not yet producing its own hormone and relies entirely on yours.
✅ Worth doing this week
- Decide about NIPT — availability, cost and turnaround vary, so ask now rather than at 13 weeks
- Switch to trousers with an elastic waist; tight waistbands are uncomfortable and pointless
- Ask about a TSH test if you have any thyroid history or symptoms
- Book the 11–14 week scan if it is not already arranged — the window is firm
- Keep up folic acid and any prescribed iron; the first trimester is not over yet
When to call your doctor
Call the same day if: you have bleeding heavier than spotting, severe or one-sided abdominal pain, shoulder-tip pain, fainting, a severe headache, a temperature above 38°C, burning on passing urine, or you cannot keep fluids down for 24 hours.
FAQ — 10 weeks pregnant
When does an embryo become a fetus?
At around 10 weeks of pregnancy, which is 8 weeks after fertilisation. The change of name marks the end of organogenesis: the major organs and structures are now formed, and the rest of pregnancy is about growth and maturation rather than construction. This is also why the period of highest vulnerability to alcohol and certain medications is now largely behind you — though neither becomes safe.
What is NIPT and when can I have it?
Non-invasive prenatal testing analyses fragments of placental DNA circulating in your blood, and it becomes possible from about 10 weeks. It screens for Down syndrome and some other chromosomal conditions with high accuracy, and it can usually determine sex. It is a screening test, not diagnostic — a high-chance result is confirmed with CVS or amniocentesis. Availability and cost vary widely by country.
How big is the baby at 10 weeks?
About 33 mm crown to rump and roughly 4 grams — strawberry-sized. This is the first week the weight is meaningful enough to state; before now it is too small to be measured routinely. The fingers are fully separated, the tail has gone, and all 20 milk-tooth buds are in place in the gums.
Should I have my thyroid checked?
It is worth asking. Your baby's own thyroid is not producing hormone yet and depends entirely on yours, and untreated hypothyroidism in pregnancy is associated with poorer outcomes. Testing TSH is not universally routine, so if you have thyroid symptoms, a family history, an autoimmune condition or a previous thyroid problem, raise it specifically rather than assuming it was covered by the booking bloods.
Week 10 at a glance
Ten weeks marks the change from embryo to fetus — 8 weeks after fertilisation — and with it the effective end of organogenesis. Your baby is about 33 mm and 4 grams, with fully separate fingers and toes, no tail, and all 20 milk-tooth buds in place. NIPT becomes possible from about now, screening for chromosomal conditions from a blood sample with no procedural risk, though it does not replace the 11–14 week scan. Your uterus has reached grapefruit size and waistbands tighten, but nausea may not have eased yet — hCG does not fall until after week 11.
Inside Baby Novum: every screening window is calculated from your own dates and surfaced before it closes, which matters most for the 11–14 week test — the one window in pregnancy that cannot be reopened once it has passed.