At 23 weeks your baby is about 28.5 cm and 500 grams — roughly a grapefruit — and the lungs have started a process that will not finish for months: producing surfactant.
The short answer: the lungs begin producing surfactant now, a substance that will eventually let the air sacs stay open after birth, though it is only the start of a process that continues maturing for months. Distinct sleep-wake cycles including REM sleep are measurable. For you, vivid or strange dreams are common, driven by hormones and the sheer amount you are thinking about the pregnancy, and mild facial puffiness in the morning is usually just fluid retention.
Your baby this week
The body is becoming noticeably more proportional this week, though the skin is still reddish and wrinkled — there simply is not enough fat underneath yet to fill it out and smooth the surface, which is a normal stage rather than anything to be concerned about.
The lungs have begun producing surfactant, a substance that reduces surface tension in the developing air sacs so they do not collapse when air is exhaled. This is an early start, not a finish line — surfactant production continues maturing for months and accelerates significantly from around 34 weeks, which is one reason later preterm births generally do better with breathing than earlier ones.
Distinct sleep and wake states are now measurable, including periods of REM sleep with substantial brain activity — a real developmental marker, even though nothing can be said about what, if anything, that activity subjectively feels like.
Your body this week
The uterus has risen roughly 3–4 cm above your navel. Many women notice their dreams becoming unusually vivid or strange around this stage — a genuine effect of hormonal changes combined with simply thinking about the pregnancy more, including during lighter sleep stages when dreams are more easily remembered.
Mild facial puffiness in the morning, easing through the day, is usually straightforward fluid retention rather than anything concerning. It is worth distinguishing from swelling that is sudden, severe, or does not ease — that combination needs assessing.
Tests and appointments
Nothing routine falls exactly at 23 weeks for most care pathways.
✅ Worth doing this week
- Do not push through tiredness — your body is spending substantial energy on growth right now
- Add magnesium-rich foods — nuts, seeds, bananas — if calf cramps have started
- Note whether morning puffiness eases by afternoon; that pattern is reassuring, persistent swelling is not
- Keep a light nearby for vivid dreams that wake you — hormonal, harmless, and worth not overthinking
- Stay hydrated, which genuinely helps limit fluid retention rather than worsening it
When to call your doctor
Call the same day if: you have bleeding, severe or one-sided abdominal pain, a severe headache with visual disturbance, sudden or severe swelling of the face and hands, fainting, a temperature above 38°C, or regular tightenings — persistent contractions this early need assessing for preterm labour rather than waiting.
FAQ — 23 weeks pregnant
What is surfactant and why does it matter?
A substance the lungs begin producing around now that reduces surface tension inside the tiny air sacs, stopping them from collapsing when air is exhaled. Without enough surfactant, breathing after a premature birth is extremely difficult, which is exactly why this week is discussed as a meaningful point — production is only beginning and continues maturing for months, with a significant acceleration from around 34 weeks.
Why is 23 weeks described as a viability milestone?
It is roughly the earliest point at which survival outside the womb becomes possible with intensive neonatal care, though outcomes at this gestational age vary enormously and improve significantly with each additional week. This is a statistical threshold discussed in medical contexts, not a target — the goal at every stage remains carrying as close to term as safely possible.
How big is the baby at 23 weeks?
About 28.5 cm and 500 grams — roughly a grapefruit. The body is becoming more proportional, though the skin remains reddish and wrinkled because there is not yet enough fat underneath to fill it out.
Do babies have sleep-wake cycles before birth?
Yes — distinct periods of active and quiet states, including REM sleep, are measurable on monitoring from around now, and brain activity during these periods is substantial. What that activity subjectively involves is not something science can determine, so it is more accurate to describe active sleep cycles than to claim anything about dreaming.
Week 23 at a glance
At 23 weeks your baby is about 28.5 cm and 500 grams, with a more proportional body, lungs that have begun producing surfactant — an early step in a process that matures over months — and measurable sleep-wake cycles including REM sleep. For you, vivid or unusual dreams are common and hormonally driven, mild morning facial puffiness that eases through the day is usually just fluid retention, and calf cramps often start, easing with magnesium-rich foods and hydration.
Inside Baby Novum: log tiredness and other symptoms as they happen, so slowing down is backed by a pattern you can actually see rather than a vague sense that something feels harder than it should.