The swallowing practice from last week continues, and the movements are growing stronger and more varied. This week brings a detail that tends to stop people mid-sentence when they hear it: your baby is already making facial expressions. Fully formed facial muscles are now producing regular, varied movements — frowning, squinting, grimacing, and what ultrasound images capture as smiling.
The eyebrows and eyelids are now fully formed — distinct, with their own individual character. The lips are becoming more defined. The foetus is, on a good quality ultrasound at this stage, beginning to look recognisably like a face rather than an abstraction. Parents who have had a 3D or 4D scan around this time often describe the experience as overwhelming — the first moment the baby looks like a specific, nameable person rather than a developmental stage.
The foetus is now 167mm — a large carrot — and has reached 360g. Growth is continuing at roughly 20–30g per week. The digestive system is processing swallowed amniotic fluid; the kidneys are producing urine; the liver and spleen are producing blood cells. The entire metabolic infrastructure of a living human body is operating, in miniature, in the dark.
We had a 4D scan at twenty-one weeks. I hadn't expected to find it emotional — I'd had the anomaly scan, I'd seen them before. But the 4D was different. I could see their face. I could see them move an arm across their eyes. And then they smiled. I know it's not a real smile. But it looked real enough. I can't explain what happened to me in that moment.
The physical experience of week 21 continues the second trimester's established rhythm, with two new developments worth naming specifically.
They are sometimes called 'practice contractions' because that is precisely what they are: the uterine muscle rehearsing for labour. They are not a sign that labour is imminent, not a sign of any problem, and not something that requires any action. They do sometimes feel alarming when they first appear — a sudden tightening across the whole abdomen can be surprising — but once recognised for what they are, most people find them entirely manageable.
When to call your midwife: if contractions are painful, regular (occurring every 10 minutes or more frequently), accompanied by lower back pain, or if you have any bleeding or fluid loss, contact your midwife. These patterns can indicate early labour, which at 21 weeks requires urgent assessment.
The bump is now fully and unambiguously visible to others — the era of strangers not being sure has passed. For most people this week marks the beginning of being visibly, publicly pregnant: people offering seats, colleagues commenting, friends reaching to touch the bump without asking. This social dimension of pregnancy is its own particular experience, with its own complexities.
Oedema (swelling) — mild swelling of the feet, ankles, and hands is common from around now, caused by the increased blood volume and fluid retention. It is typically worse at the end of the day, in hot weather, and after prolonged standing. Elevating feet when resting and staying active helps. Sudden, significant, or asymmetric swelling — particularly of the face and hands — warrants same-day contact with your midwife as it can indicate pre-eclampsia.
Skin sensitivity on the abdomen — as the bump grows, the skin stretches and can feel sensitive, itchy, or tight. A simple, fragrance-free moisturiser applied regularly helps with comfort.
The first week after halfway has a particular emotional quality: the milestone of week 20 has been absorbed, and the pregnancy is now in full public existence. The second half has begun. The bump is something other people can see, react to, and comment on. For many people this is a new and not always straightforward social experience.
Strangers touching the bump without asking is one of the more commonly cited frustrations of mid-pregnancy. It is, simply put, not acceptable behaviour — your body remains your own — and you are entirely entitled to say so, however you choose to do it. "I'd rather you didn't" is complete. You don't owe anyone an explanation. Being visibly pregnant does not transfer any ownership of your body to people who happen to notice.
A woman in a supermarket reached over and touched my bump at twenty-one weeks without a word. I was so startled I didn't say anything. Then I thought about it for three days. Now I have a polite but definite response ready. Nobody else has tried since. You're allowed to have a boundary.
Comments about the size of the bump — "you're huge!", "is it twins?", "you're so small for 21 weeks" — are similarly unhelpful, however well-intentioned. Bump size varies enormously between pregnancies and between bodies, and none of these observations are medically meaningful. You are not obliged to engage with them or find them funny.
The emotional interior of this week, for most people, is genuinely positive. The facial expressions detail tends to produce a particular kind of joy — the recognition that this is already a face, already practising, already itself. The movements are daily company. The pregnancy is more than half done. The best of the second trimester is still in play.
The themes of week 21 connect to these full topic guides.
The pregnancy's full social visibility from this week onwards changes the texture of daily life for both of you. Your partner is now navigating a world of unsolicited comments, unexpected physical intrusions, and a constant external emphasis on their body and its contents. Being a quiet ally in navigating that — backing up their choices about how to respond, not finding the intrusions funny when they find them irritating, not inviting more commentary — is useful in a way that's easy to underestimate.
The Braxton Hicks contractions, if they arrive, may be startling the first time. Knowing what they are in advance — harmless uterine practice, entirely normal — means neither of you is alarmed unnecessarily. If your partner feels a tightening and isn't sure whether it is Braxton Hicks or something else, the distinguishing features are worth knowing: irregular, painless, stopping when they change position or activity, not accompanied by other symptoms.
- You may be able to feel the baby move now. The kicks at 21 weeks are strong enough that a hand pressed to the bump at the right moment will sometimes detect them. Ask to try when your partner is feeling active movement. The first time you feel it from the outside is its own significant moment.
- Back up the bump boundary. If someone reaches for the bump in a social situation, you can be the one who intercepts or redirects without your partner having to manage it themselves every time. "She'd rather you didn't, thanks" is complete and unchallengeable.
- Antenatal classes. If these aren't booked, they need to be now — urgently. The best ones run from around weeks 25–32 and fill up significantly in advance.
Read about pre-eclampsia and know the warning signs. Pre-eclampsia is a condition specific to pregnancy — caused by a problem with the placenta — that can develop from around week 20 onwards. It affects around 6% of pregnancies. Most cases are mild and well managed; untreated, it can become dangerous to both mother and baby. The key is recognition and early reporting.
Severe headache that doesn't respond to paracetamol
Sudden or significant swelling of face, hands, or feet
Vision changes — blurring, flashing lights, seeing spots
Pain just below the ribs on the right side
Vomiting alongside any of the above
These symptoms individually can have benign explanations. Together, or persistently, they require same-day assessment. Do not wait for the next scheduled appointment. Do not Google and reassure yourself. Call your midwife or maternity triage.
As the third trimester approaches over the coming weeks, this is a useful question to begin raising:
Formal movement monitoring becomes important from around week 24–28, when a consistent pattern has established itself. Understanding the guidance in advance — including the Tommy's principle that there is no safe number of movements per day and that any reduction in your normal pattern is worth reporting same-day — means you will have the framework before you need it, rather than trying to understand it in a worried moment at 2am.