The term 'viability' in pregnancy refers to the gestational age at which a baby born prematurely has a reasonable chance of surviving with intensive medical support. In the UK, week 24 is the threshold recognised by the NHS and in law — it is the earliest point at which active resuscitation and neonatal intensive care would routinely be offered.
I didn't expect twenty-four weeks to feel as significant as it did. I'd been following the guide and knew it was coming. But when I actually woke up on the morning of exactly twenty-four weeks, I sat in the kitchen for a long time. Something had changed. I couldn't explain it precisely, but something had changed.
The senses that sharpened last week continue their development. The movements, the expressions, the startle responses — all continuing, all becoming more consistent. This week adds the most significant physiological development of the second trimester: the lungs have begun producing surfactant.
In premature babies born before surfactant production is established, respiratory distress syndrome (RDS) is the primary cause of critical illness. Surfactant therapy — introducing artificial surfactant directly into a premature baby's lungs — is one of the most significant advances in neonatal medicine and is a routine part of care for very premature babies. The fact that your baby's lungs are beginning to produce surfactant this week is not only developmentally significant; it is, mechanistically, what makes viability possible.
The baby has reached 210mm and 600g. The fat that will eventually give newborns their characteristic rounded softness is beginning to accumulate under the skin, though the baby at 24 weeks still looks quite lean compared to a full-term newborn. The eyelids, sealed since week 8, are beginning to show the first signs of preparing to open — they will unseal at around week 26. The brain is developing its complex folded surface rapidly, with new folds appearing week by week.
My neonatologist friend explained surfactant to me when I was pregnant and I've never forgotten it. The idea that one substance — barely there at 24 weeks, fully established by 36 — is what stands between breathing and not breathing. And that it begins now. It made week 24 feel like the most important piece of biology I'd ever learned.
The physical experience of week 24 continues the pattern of the mid-second trimester, with no dramatic new changes this week. The bump is large enough to be measurably tracked at each appointment; the fundal height at 24 weeks should be approximately 24cm. The movement patterns established over the last few weeks are consistent and reliable enough to form a genuine baseline — and from this week, any reduction in that baseline is something to report to your midwife the same day.
Any reduction in your baby's normal pattern of movement should be reported to your midwife or maternity unit the same day — not the next scheduled appointment, not after a nap to see if things improve, not after eating something sweet. Same day.
There is no 'safe number' of movements per day. What matters is deviation from your baby's individual normal. If something feels different — fewer movements, weaker movements, a change in character — contact your unit. They will not think you are overreacting. They want you to call.
Week 24 carries a particular emotional quality that is unlike any other week in the pregnancy. For many people it produces a kind of quiet, significant relief — a threshold has been crossed, a number has been reached, and something has changed in how the pregnancy is understood and experienced. The crossing is not a guarantee of anything; it is not a removal of risk. But it is a meaningful shift, and the feeling that accompanies it is real and worth acknowledging.
For people who have had pregnancy losses, premature births, or fertility challenges, week 24 can be particularly charged — a milestone that has perhaps been counted toward for a long time, or one that previous pregnancies did not reach. If this is you, the way you experience this week may be different from the above description: more complex, more weighted with history, more cautious about relief. That is entirely valid. The milestone is still worth marking, even quietly.
I'd had a loss at twenty-two weeks in a previous pregnancy. Reaching twenty-four weeks in this pregnancy felt like crossing a line I'd spent two years thinking about. I didn't celebrate exactly — it felt too serious for celebration. But I acknowledged it. I sat with my partner and we both acknowledged it. That was enough. More than enough.
For the majority of people in straightforward pregnancies, week 24 is also simply a good week — solidly in the second trimester's most comfortable stretch, with movements as daily company, a clearly visible bump, and the horizon of the third trimester not yet close enough to feel pressing. The balance between looking forward and being present in this exact moment is about as good as it gets.
The themes of week 24 connect to these full topic guides.
Week 24 is a milestone that belongs equally to both of you. The months of support, adaptation, and sustained presence have been building toward something — a pregnancy that has reached a point of genuine significance. Acknowledging that together, even simply, is worthwhile. Not with grand celebration, but with recognition.
From this week, foetal movement monitoring becomes a shared responsibility in a new sense. You should both know that reduced movement requires same-day contact with the midwife or maternity unit. You should both know the number. If your partner is asleep or unavailable and you notice the baby hasn't been moving, you should be confident enough in the guidance to act on it — not to wake your partner unnecessarily, but to know what the right response is.
- Mark this week somehow. A meal, a conversation, a shared acknowledgement of where you are. Week 24 is one of four genuinely significant milestones in pregnancy — alongside the 12-week scan, the halfway point, and the 36-week milestone. It deserves to be named.
- Know the movement guidance. Read Tommy's guidance at tommys.org. Understand that there is no safe number of daily movements, and that any reduction in normal pattern is a same-day call. Save the maternity triage number in your phone.
- The third trimester is eight weeks away. The final preparation window — antenatal classes, birth preferences, practical baby preparation — has a real horizon now. Use the time well.
Mark week 24. This is not a medical task. It is a human one. You have carried this pregnancy for twenty-four weeks. You have navigated the first trimester, the scans, the anxiety, the physical demands, the halfway point, and the sharpening sensory world of the second trimester. The baby inside you is viable. Take a moment with that — a photograph, a journal entry, a conversation, a meal. The milestone is real. It deserves acknowledgement from the person who has done the most to reach it.
— Confirming your glucose tolerance test has been arranged if you have any risk factors for gestational diabetes
— Ensuring your maternity triage number is saved in both your phone and your partner's
— Reviewing your birth preferences progress — what's been decided, what still needs thought
— Confirming antenatal classes are booked if they haven't been already
At your next appointment — and from now on, at every appointment — confirm the movement guidance clearly:
Having this confirmed verbally by your midwife — rather than relying on having read it here — matters. It creates a clear, shared understanding of the expectation, and it means that if the moment ever comes, you will act without hesitation. Delayed reporting of reduced movement is one of the most avoidable contributors to preventable stillbirth. Every pregnancy deserves a clear, confirmed plan.