Week eighteen — the anatomy scan is approaching. Write down how you're feeling ahead of it.
Open my diary →Set week 18 in the app for your tracker, diary prompt, and the second trimester lesson — free, always.
Open app — it's freeBrown fat continues accumulating from last week, and the skeleton's progression from cartilage to bone continues steadily. This week brings one more layer of physical preparation — both literal and remarkable: your baby is now covered in vernix caseosa.
The foetus is now 140mm — a sweet potato — and has reached 190g. The movements that have been present since around weeks 14–16 are becoming stronger and more frequent. Some people begin to feel movement from the outside of the abdomen for the first time around now, though this is more commonly possible from weeks 20–22. The kicks are not yet forceful enough for a hand pressed against the abdomen to reliably detect them; that comes later.
The foetus's bones, while hardening progressively, are still pliable enough to flex and compress during birth. The skull bones in particular are designed to overlap slightly — a process called moulding — allowing the head to navigate the birth canal. This is why some babies are born with temporarily elongated or misshapen heads that return to a rounder shape within the first days of life.
The midwife explained vernix to me at the twenty-week scan and I immediately felt guilty for not knowing about it. All that time it had been there, this whole protective system already running, and I'd had no idea. I made a decision then not to wipe it off at birth. It stayed on her for hours. It felt important.
The 20-week anomaly scan — which is offered between weeks 18 and 20 on the NHS — is the most detailed clinical assessment of your pregnancy between the first trimester and birth. It is significantly more comprehensive than the 12-week dating scan and covers a much wider range of structures. Understanding what it involves, what it can and cannot detect, and how its findings are communicated allows you to approach it as an informed participant rather than an anxious observer.
We decided not to find out the sex. The sonographer was brilliant — she told us she could see but wouldn't say, and she turned the screen slightly at one point without making a thing of it. It felt completely respected. I'd been worried it would be awkward. It wasn't at all.
Week 18 continues the physical progression of recent weeks with a few things worth noting specifically. The uterus is now roughly the size of a cantaloupe melon and sits clearly above the navel — the fundal height is measurable externally and your midwife will begin tracking it at appointments from around now as a simple but effective indicator of foetal growth.
For people who haven't felt movement yet, week 18 is within the range where first movements commonly arrive for first-time parents. The window is broad — weeks 16 to 22 — and position of the placenta, body composition, and individual sensitivity all play a role. If you are approaching week 20 without any sensation of movement, mention it at the anomaly scan appointment; it is not automatically a concern, but it is worth checking.
The anomaly scan tends to occupy significant emotional space in the days approaching it, and the experience of it — whether it happens this week or in the next couple of weeks — is one of the most emotionally complex of the whole pregnancy. More so, for many people, than the 12-week scan: the 12-week scan was primarily about viability and relief; the anomaly scan is about something more structural and therefore more permanent-feeling.
Many people also describe the anomaly scan as the most visually impressive: the baby is now large enough to see clearly, moving, recognisably formed, with a face and discernible features. For partners, who may have found earlier scans more abstract, this is often the moment the baby becomes fully real. For the person carrying the pregnancy, it can mark a shift too — from knowing there is a baby to seeing, clearly, that this is a specific, distinct, already-individual person.
The anomaly scan was nothing like I'd expected. I'd steeled myself for a clinical, anxious experience. Instead they showed us the face, the profile, the hands opening and closing. The sonographer said "there's a cheeky one" when the baby put their hand in front of their face. I laughed. I hadn't expected to laugh. It was the most I'd felt like a parent so far.
If the scan identifies something that requires follow-up, the immediate period — receiving the information, processing it before any further appointments — is typically the hardest. Take someone with you if at all possible. Ask as many questions as you need. Know that you do not have to make any decisions in the room. The support available — from your midwife team, from the antenatal diagnostic service, and from organisations like Antenatal Results and Choices (arc-uk.org) — is there specifically for this.
The themes of week 18 connect directly to these full topic guides.
The anomaly scan is one of the appointments where being present matters most. For many partners, it is the most visually and emotionally significant moment in the pregnancy so far: the baby is large enough to see clearly, to watch moving, to have a face that is recognisably a face. This is typically the moment of deepest engagement for partners who have found the earlier weeks more abstract.
Come prepared: know what is being checked, have decided together about the sex, and have had the brief but important conversation about what you would want to do if the scan identified a finding requiring follow-up. Not because it is likely — most anomaly scans are normal — but because having spoken about it means you are not navigating a significant decision in shock.
Make a note about vernix — and decide now whether you want it left on at birth. This sounds premature, but birth preferences are best thought through from a position of calm curiosity rather than in the intensity of labour or the immediate postpartum. Vernix is one of the things most people don't know to ask about, and many hospitals still have a default of wiping it away. If you want it left on or massaged in — which the evidence supports — putting it in your birth preferences now means it doesn't rely on you remembering to say so in the room.
Once the sonographer has completed their checks and given you the headline results, ask:
Placenta position matters: a low-lying placenta at 20 weeks is common (around 1 in 20 pregnancies) and often resolves by 32 weeks as the uterus grows. But it requires a follow-up scan to confirm, and if it doesn't resolve it affects birth planning significantly. Knowing this early allows for appropriate monitoring. The second part of the question gives the sonographer space to mention anything that didn't rise to the level of a formal finding but is worth noting — a small soft marker, a borderline measurement — that you would benefit from knowing rather than discovering at a later appointment.