Quick answer: At 23 weeks your baby is about 28.9cm and 500 grams, and from this week a baby born prematurely has a chance of survival with specialist neonatal care. Swimming is one of the best pregnancy exercises: the water supports your bump and eases joint pressure. Avoid diving, hot tubs, steam rooms and saunas. Call your midwife or maternity unit immediately if your baby's movements slow down, stop or change, and get sudden breathlessness checked straight away.
What parents need to know
Week 23 marks a significant, if bittersweet, medical milestone: from this week, a baby born prematurely has a chance of survival with specialist neonatal care. Of course, the goal is for your pregnancy to continue as long as possible — but this is a reminder of how remarkable your baby's development has been over these weeks.
How big is your baby at 23 weeks?
Your baby is now about the size of a large mango, approximately 28.9cm from crown to heel and weighing around 500 grams. Half a kilogram of human life, fully formed and increasingly capable.
What's happening with your baby?
Your baby's lungs are developing rapidly, producing a substance called surfactant, which keeps the air sacs open so the lungs can function after birth. This is one of the key developments happening from around 23 weeks, though the lungs won't be fully mature until much later in pregnancy. Your baby now has regular sleep-wake cycles and may be making distinct movements — kicks, rolls, and stretches — that you can feel from the outside of your bump.
Your baby's sense of balance is developing, facilitated by the vestibular system in the inner ear. Their skin is becoming less transparent as more fat builds up beneath it, though it's still quite wrinkled at this stage. Your baby's hands are fully formed and increasingly active.
The benefits of swimming in pregnancy
Swimming is widely regarded as one of the best forms of exercise during pregnancy, and for good reason. The buoyancy of the water supports your growing bump, relieving the pressure on your joints and spine that becomes more pronounced on land. It's a low-impact, full-body workout that can be continued safely throughout all three trimesters (unless your midwife has advised otherwise). Do not lie flat on your back for long periods, particularly after 16 weeks, because the weight of your bump presses on the main blood vessel bringing blood back to your heart, and this can make you feel faint.
Benefits of swimming during pregnancy include reduced back pain and pelvic girdle pain thanks to the supportive nature of water, improved cardiovascular fitness and stamina for labour, reduced swelling in the legs and ankles, better sleep (many women report improved sleep quality after swimming), and a positive effect on mood and anxiety levels. Aquanatal classes (antenatal exercise classes specifically designed for pregnant women and held in swimming pools) are available at many leisure centres across the UK and are an excellent option.
You don't need to be an experienced swimmer to benefit. Gentle breaststroke, walking in the water, or participating in an aquanatal class are all worthwhile. Avoid diving or jumping into the pool, and don't use hot tubs, steam rooms, or saunas, which can raise your core temperature dangerously. Do not go scuba diving while you're pregnant, because your baby has no protection against decompression sickness and gas embolism (gas bubbles in the bloodstream).
What's happening in your body?
At 23 weeks, many women notice that their bump has become quite substantial and that physical discomforts are increasing. Breathlessness can occur as the growing uterus begins to push against the diaphragm. This is normal, but breathlessness that comes on suddenly, being out of breath when you're lying down, or breathlessness with dizziness needs to be checked straight away: call your midwife or maternity unit, or NHS 111. Call 999 or go to A&E if you have severe difficulty breathing, pain in your chest or upper back, a very fast heartbeat, or you pass out. Haemorrhoids (piles) are another common pregnancy complaint, caused by increased blood flow and pressure from the uterus. A high-fibre diet, plenty of fluids, and regular movement can help prevent constipation, which worsens haemorrhoids. Some creams and medicines can soothe piles. Ask your midwife, GP or pharmacist to suggest a suitable treatment, tell them you are pregnant, and do not use a cream or medicine without checking with them first.
When to get help
Some symptoms in pregnancy can be a sign of something serious and need checking quickly. This is who to contact, and how soon.
Call 999 if:
- you're bleeding from your vagina and the bleeding is heavy (soaking a period pad soon after putting it on), or you also have severe pain in your tummy, pain in your shoulder, or feel sick, faint, dizzy or lose consciousness
- you think your baby is coming now and you have a strong urge to push (ask for an ambulance)
- you have severe difficulty breathing (you're gasping, choking or not able to get words out) or your chest feels tight or heavy
- you have pain and swelling in one leg and you also feel short of breath or have chest pain. A blood clot in the leg can travel to your lungs, which can be life-threatening
- you have possible signs of sepsis, such as breathing very fast, being confused or having slurred speech, blue, pale or blotchy skin, a rash that does not fade when you press it, or a very high or very low temperature. Being pregnant makes sepsis more likely
- you do not feel you can keep yourself safe (a mental health emergency is as serious as a physical one)
Always call 999 if you think it's a life-threatening emergency, no matter what stage of pregnancy you are.
Call your midwife or maternity unit now if:
- your baby is moving less than usual, you cannot feel your baby moving anymore, or there is a change to your baby's usual pattern of movements
- you have light bleeding or spotting, even if you have no pain or only mild tummy pain
- you have stomach pain that is severe or does not go away after you've rested for 30 to 60 minutes, or stomach pain with regular cramping or tightenings, lower back pain, or pain when you pee
- you're less than 37 weeks pregnant and you have a gush or trickle of fluid from your vagina (this could be your waters breaking), regular contractions or tightenings, period-type pains, or backache that's not usual for you
- you have signs of pre-eclampsia: a severe headache that does not go away with simple painkillers, vision problems (such as blurred vision or seeing flashing lights), pain below the ribs, sudden swelling of the face, hands or feet, feeling very unwell, heartburn that does not go away with heartburn medicines, or being sick (vomiting)
- your skin is very itchy (for example, it keeps you awake at night), the palms of your hands or soles of your feet are itchy, or the itching is worse at night. This can be a sign of a liver condition called intrahepatic cholestasis of pregnancy (ICP) that needs urgent treatment
- your breathlessness comes on suddenly, you're out of breath when you're lying down, or you're breathless and also have chest pain or feel dizzy
- you have pain or swelling in one leg, usually in the calf or thigh. This could be a blood clot (deep vein thrombosis, or DVT), which is more likely when you're pregnant
- you have a high temperature (38C or above), or you feel hotter than usual or shivery. A high temperature can be a sign of an infection, so it's important to get it checked
If your baby's movements change, do not wait until the next day: call immediately, even if it's the middle of the night. Do not use a home doppler to check the heartbeat yourself. Even if you hear a heartbeat, this does not mean your baby is well.
If you cannot reach them, or you're not sure what to do, call NHS 111.
Speak to your midwife or GP if:
- you have not felt your baby move by 24 weeks. Most people start to feel movements between 16 and 24 weeks. If this is your first baby, you might not feel them until after 20 weeks
- you're worried about your mental health, or stress, anxiety or low mood are affecting your day-to-day life. If you need urgent help for your mental health, call 111 and select the mental health option, or ask for an urgent GP appointment
Your week 23 checklist
This week:
- Try a swim or look for aquanatal classes near you.
- Maintain a high-fibre diet to prevent constipation and haemorrhoids.
- Mention any breathlessness to your midwife.
- Continue daily pelvic floor exercises.
- Keep an eye on your baby's movements, and call your midwife or maternity unit immediately if you notice any change in their usual pattern.
Related guides
Sources & further reading
- NHS — You and Your Baby at 23 Weeks Pregnant
- NHS — Exercise in Pregnancy
- Tommy's — Week 23 of Pregnancy
- NCT — Week 23 of Pregnancy
General information, not individual medical advice. Speak to your GP, midwife or health visitor about your baby’s needs.
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