Week 23 of pregnancy: Why the size and weight of your baby are only approximate values

Size of your baby in week 23

Your baby is between 28 and 30 cm long from the top of their skull to their heels, about the size of a savoy cabbage.

It may not be possible to measure the full length of the foetus because of its position and activity. If so, the length of the femur, also known as the thighbone and the longest bone in the human skeleton, can be used instead. To determine your baby’s size, your doctor will use a formula which involves multiplying their femur length by 7. This measurement, together with head circumference, biparietal diameter and abdominal circumference, results in an estimate of your baby’s overall size.

Your baby can’t yet be measured with a tape measure or ruler, so these values are approximate and may be below average. Measurement errors can occur, especially if your baby is very active, and each baby is unique, of course, thanks to the genetic material from their parents and family. 

Their weight (around 450 grams in week 23) should also only be regarded as an approximate value. They will grow longer and put on weight at different times – their body can’t really do both simultaneously – and this is why it may seem like there are short “pauses” in either aspect of their development. So don’t worry if they don’t appear to be getting longer or putting on weight at any one time.

Your baby’s development

In week 23, your baby develops a crucial organ for producing hormones and regulating their sugar metabolism: the pancreas. Located behind the stomach, it’s best considered a gland – in fact it’s the largest gland in the human body at 15-20 cm long. It contains what are known as the islets of Langerhans, which produce the crucial hormone insulin that your baby needs to break down sugar and regulate the level of sugar in their blood.

There’s still plenty of space in your womb for your baby to move around, and they’ll be taking full advantage of this to train their muscles, tendons and joints and to hone their senses. If the turbulence in your belly is such that you think you might be expecting twins, it’s probably because your baby is moving quickly from one part of the womb to another. This will happen less over the next few weeks as they have less and less space for these “trips”.

Inside the womb, the amniotic cavity now contains half a litre of amniotic fluid at all times. This fluid is regularly exchanged via the placenta, and the amount of fluid will increase as your pregnancy progresses. Every day your baby drinks around 400 millilitres of it, which helps train their digestive system.

From now on, each week improves your baby’s chances of survival in the event of a premature birth. Modern medicine and innovative technology enable premature babies to be supplied with everything they need and the environment of the womb to be recreated.

Nonetheless, a premature birth is an extremely difficult process for a mother and baby to go through. The appointments you have with your gynaecologist will help reduce this risk.

What it’s like for the mum-to-be in week 23

Every time you step on the scales will confirm that you’re putting on weight, and you’ll gain somewhere between 250 and 300 grams in week 23. It may be a bit more than that – and that’s absolutely fine.

If you want, you can check your weight using our pregnancy weight calculator to make sure that everything’s within the recommended range.

You might notice that you quickly get tired and have no energy. This is because your body is working extremely hard to rise to the challenge of supporting a healthy developing baby. From week 23, you should generally avoid strenuous activities and long walks or hikes. It may be that you still feel fit and, if so, there’s no reason to stop these activities – though it’s best to slow down a bit while you’re doing them.

Common signs and symptoms

Increased need to pee

You won’t be able to go very far or very long without going to the toilet, as you’ll need to pee more often. It’s caused by your womb putting pressure on your bladder, which gets smaller as a result. However, this isn’t a reason to drink less – make sure you keep your fluid intake up, as your body really needs it during pregnancy.

Feeling tired and weak

If you often feel tired and weak even though you haven’t been exerting yourself too much, it may be that your body doesn’t have enough iron. Around 20% of pregnant women experience this in week 23.

If you feel faint, your skin goes pale and even a good rest doesn’t leave you feeling refreshed or reinvigorated, you should take a special supplement to boost your iron levels and ensure your baby continues to get the oxygen they need.

Find out more about iron and which foods contain high amounts of it.

Your blood pressure may also be why you find it difficult to get going and feel weak. Many pregnant women suffer from low blood pressure in the middle weeks of pregnancy in particular, as their circulatory system tries to handle the increased blood flow and supply blood and nutrients to the placenta. Your doctor or midwife will regularly measure your blood pressure and can tell you how to increase it if it’s too low.

Top tips

  • Get hold of a maternity panty girdle if you can, as this will support your belly.
  • Find out more about nappies and nappy changing techniques.
  • Colouring books for adults or mandalas are a good way to relax and take your mind off things.
  • Ask your midwife about breastfeeding equipment and books you can read about breastfeeding.
  • When you get cravings for sweets, try to eat fruit and vegetables instead. 

Questions you may want to ask your doctor or midwife

Breastfeeding is best for your baby

Now is a good time to ask your midwife about how breastfeeding works. It’s essentially a question of supply and demand: your child will set the breastfeeding pattern, and your body adapts to it. During the first few days and weeks after the birth, it’s crucial that you and your baby bond in order to establish a good breastfeeding pattern.

Understanding how breastfeeding works (and learning from other mums) will help you handle any problems or crises that can occur early on.

Your midwife can tell you which breastfeeding equipment you need to buy, and which equipment you can borrow if necessary.

Low iron levels or low blood pressure

If you feel tired and weak all the time, and it’s affecting your everyday life, then get your doctor to check your iron levels and blood pressure. After all, if you’re not feeling well, then your baby won’t be feeling well either.

Information about the author:

Juliane Jacke-Gerlitz is a registered nurse. She has been working in the field of mother and breastfeeding counselling for more than ten years. Currently she is working as a medical writer and psychological consultant. Juliane Jacke-Gerlitz has been married for 22 years, is a mother of eight children and lives with her family in Halle.