The face that was fully formed last week is now animated with daily movements, expressions, and — this week — something new: a startle reflex triggered by sound. Your baby's hearing is fully developed, and loud or sudden noises from the outside world can cause them to jump — a rapid, full-body flinch in response to the unexpected. You will feel this as a sudden, distinct movement quite different from the rolls and kicks of deliberate activity. It is one of the clearest demonstrations of sensory connection between the outside world and the world inside.
Beyond the startle response, all the senses are sharpening rapidly this week. Hearing is fully developed and perceptive — the baby is processing the rhythmic, familiar sounds of your heartbeat and digestion as constant background, and distinguishing these from new sounds outside. Touch has been developing for weeks and is now acute enough to detect changes in temperature and pressure. Taste is active. The eyes, while still sealed, are sensitive to light. The only sense not yet functional is smell — and even that begins its development in the coming weeks as the nasal passages open and begin to sample the amniotic fluid.
The baby has crossed the 500g threshold — an aubergine — and has reached 200mm. The weight gain in the second half of pregnancy will accelerate dramatically from around week 28, as fat deposition begins in earnest. For now, the body is still relatively lean — the characteristic roundness and softness of a newborn lies ahead.
I was watching a film with the volume up at twenty-three weeks and the baby jumped so hard I gasped. I hadn't expected it at all — this sudden kick from inside in direct response to the film's jump scare. I laughed for about five minutes. We were both startled. It felt deeply companionable.
Week 23's physical experience continues the patterns of recent weeks, with a few specific developments worth naming.
The physical discomforts introduced in weeks 21–22 — round ligament pain, Braxton Hicks, heartburn, sleep difficulties, possible pelvic girdle pain — are all continuing. Week 23 does not introduce dramatic new physical changes; it deepens the established experience of the mid-second trimester. The main shift at this stage is the increasing visibility and solidity of the bump — measurably larger week by week, increasingly part of how you move through space and relate to the physical world.
The startle detail of this week tends to produce a specific kind of delight — a new form of connection, sudden and physical and mutual, between the world you are in and the world the baby is in. Being startled together by the same thing at the same moment is one of the most unambiguous ways that shared experience becomes possible in pregnancy. You are not just aware of them; you are having experiences alongside them.
The approaching viability milestone of week 24 — one week away — begins to occupy emotional space from about now. For many people it is a source of quiet, growing relief: the knowledge that survival outside the womb, while still requiring intensive neonatal support at this stage, is becoming possible. For others who have had premature births or pregnancy losses, the approach of week 24 can be more complex — a milestone weighted with history. Both responses are valid and deserve to be acknowledged rather than managed away.
I counted the days to twenty-four weeks with a kind of intensity I hadn't felt since the twelve-week scan. Not because I expected anything to go wrong, but because I'd read about viability and it meant something to me — this shift from theoretical to possible. The week leading up to it was quietly electric.
Birth preparation continues to be the most useful thing you can be doing with the energy and clarity of the mid-second trimester. The window of relative physical ease — before the third trimester's demands establish themselves — is still open. Antenatal classes, birth preference conversations, reading about newborn care, thinking about maternity leave and support: all of this is easier now than it will be at 34 weeks.
The themes of week 23 connect to these full topic guides.
The startle response this week offers a concrete, accessible experience of connection — if a sudden loud noise causes a visible or felt movement, that is a moment that belongs to all three of you. It is also a reminder that the baby is already a participant in shared experience, already responding to the same world you are both in. This has been gradually true since week 16, but the startle response makes it physical and immediate in a new way.
Week 24's viability milestone is one week away, and for many partners it carries its own emotional weight — a shift from the abstract to the more concrete. Understanding what viability means and does not mean, and approaching the milestone without either catastrophising or dismissing it, is the right register.
- Be aware of volume around the bump. Loud, sudden sounds — music, television, arguments, doors slamming — are felt by the baby as well as heard. This isn't a reason to live in silence, but it is worth knowing that the environment you're creating is also the environment they are experiencing.
- Attend the 24-week appointment if there is one. Not all trusts schedule a specific 24-week appointment, but some do. Check what your trust offers and attend if possible — the milestone matters and being present for it is worthwhile.
- Talk to the bump. At 23 weeks, fully developed hearing means your voice is being heard clearly, regularly, and already associated with safety. The familiarity built between now and birth matters — newborns respond to familiar voices from their first hours. You are laying that groundwork now.
Read Tommy's guidance on foetal movement monitoring — now, before week 24. From week 24 onward, any reduction in your baby's normal movement pattern is something to report to your midwife or maternity unit the same day. Understanding the guidance before you need it — rather than trying to find and interpret it at 2am when worried — means you will respond appropriately and promptly when it matters.
Do not use a home Doppler to check for a heartbeat. Detecting a heartbeat is not the same as assessing foetal wellbeing. A Doppler can give false reassurance when movement has genuinely reduced and assessment is needed. If you are concerned about movement, contact your midwife — not a home device.
Contact your midwife if you notice reduced movement — same day. Don't wait. Don't eat something sweet and see if that makes them move. Call. Being assessed and everything being fine is the outcome almost every time, and there is no such thing as contacting your maternity unit too often about reduced movement.
Tommy's full guidance is at tommys.org/pregnancy-information/pregnancy-complications/reduced-movement — worth reading and bookmarking now.
At your next appointment, ask clearly:
Having the specific number and process clearly in your head — rather than a general sense that you should "call someone" — means you will act faster and more confidently if you need to. Ask your midwife to confirm the out-of-hours number for your maternity unit as well as the daytime route. Write it in your phone. You will very likely never need it urgently, but having it precisely to hand removes a barrier to the right response.