At 15 weeks your baby is about 15 cm and 70 grams — apple-sized — and has just gained a sense that will not become vision for months: the ability to detect light through closed eyelids.
The short answer: the eyes are still sealed shut but can now sense light, taste buds are fully functional and picking up flavours through the amniotic fluid, and the bones continue hardening. Skin is thin enough that blood vessels show through on a scan — normal for this stage. For you, breathlessness on exertion is common, and this is the window for the quad blood test if the 11–14 week screening was missed.
Your baby this week
The eyelids remain fused, but the eyes underneath can already register light, and studies have shown a fetus turning away from a bright light held against the mother's abdomen. Full vision is a long way off — the eyelids will not open until around week 26.
Taste buds are fully developed, and the amniotic fluid genuinely carries flavour from what you eat, so the fetus is already being exposed to the tastes that will surround it after birth. Bones continue hardening through ossification, a process that continues well into childhood.
The skin is still thin and largely transparent, which is why blood vessels are visible on ultrasound. It will thicken and gain an underlying fat layer over the coming months.
Your body this week
Breathlessness on exertion often becomes more noticeable this week. It is driven by progesterone raising your respiratory rate to increase oxygen delivery, and it happens long before the uterus is physically large enough to restrict your diaphragm — that mechanical breathlessness comes much later. Your heart is also working harder, with cardiac output continuing its rise through the second trimester.
Pregnancy rhinitis, if it started last week, often continues. Gums may still be sensitive, and a professional cleaning now — with your dentist told you are pregnant — is a reasonable thing to book.
Your centre of gravity is shifting further forward as the uterus grows. Good posture now genuinely reduces the back pain that tends to build through the second and third trimesters, rather than merely masking it later.
Tests and appointments
Tests and scans around now: Where first-trimester screening was missed, the quadruple blood test is offered between 15 and 20 weeks.
Exact timing varies by country and by your own care plan — your doctor or midwife will confirm the schedule that applies to you.
If the combined test at 11–14 weeks was not done, the quad test is the alternative and this window opens now. It is a blood test only, with no procedural risk, but its detection rate is lower than the combined test's. A high-chance result leads to the same next steps — NIPT or a diagnostic test.
✅ Worth doing this week
- Ask about the quad test now if first-trimester screening was missed — the window is open but will close
- Practise good posture deliberately; it is easier to build the habit before the bump makes it obvious why
- Book that dental clean if gums have been an issue
- Pace exertion rather than pushing through breathlessness — pregnancy is not the time to chase a personal best
- Keep taking prenatal vitamins; the demands on your iron and calcium are climbing now
When to call your doctor
Call the same day if: you have bleeding, severe or one-sided abdominal pain, breathlessness at rest or with chest pain or a fast heart rate, a severe headache with visual disturbance, fainting, or a temperature above 38°C. Breathlessness that stops you completing a sentence is different from ordinary pregnancy breathlessness and should not wait.
FAQ — 15 weeks pregnant
Can the baby see anything at 15 weeks?
Not images — the eyelids are still fused shut and will not open until around week 26. But the eyes can already detect light through the closed lids, and a bright light against your abdomen can make a fetus turn its head away. This is light sensitivity, not vision.
What is the quad test and who needs it?
A blood test measuring four markers — AFP, hCG, oestriol and inhibin-A — offered between 15 and 20 weeks, mainly to women who missed the 11–14 week combined screening or who want a second data point. It screens for Down syndrome, some other chromosomal conditions and neural tube defects, but it is less accurate than the combined test and, like it, gives a probability rather than a diagnosis.
Why is my baby's skin described as see-through?
At 15 weeks the skin is still very thin and has not yet developed the fat layer underneath that makes it opaque. Blood vessels are visible through it on a scan, which can look startling but is completely normal for this stage — the same reason premature babies born very early have translucent-looking skin.
Why am I more breathless at 15 weeks?
Progesterone increases your breathing rate well before the uterus is large enough to press on your diaphragm, so mild breathlessness on exertion is common and normal now. It becomes a concern if it happens at rest, comes with chest pain, or is accompanied by a fast heart rate — those need same-day assessment rather than being put down to pregnancy.
Week 15 at a glance
At 15 weeks your baby is about 15 cm and 70 grams, with fully working taste buds, eyes that can detect light through fused lids, and bones that continue hardening. Skin is thin enough for blood vessels to show through — a normal stage, not a concern. For you, breathlessness on exertion is common as progesterone raises your breathing rate, well before the uterus is large enough to press on the diaphragm mechanically. This is also the window for the quad blood test if earlier screening was missed.
Inside Baby Novum: the weekly guide explains what is typical for your exact stage in plain language, so a new sensation like breathlessness can be checked against what is expected rather than searched from scratch.