Week-by-week guide to pregnancy

group of pregnant women
When you're pregnant, you have lots of questions. Our week-by-week pregnancy guide is packed with lots of useful information. From what's happening inside your body, to how your baby is developing, and tips and advice on having a healthy pregnancy – this is your one-stop pregnancy guide!

2nd trimester

Our week-by-week pregnancy guide is full of essential information. From staying fit in pregnancy to advice on your maternity rights, you'll find it all here.

Week 16 – your 2nd trimester

Your baby is growing quickly and about to have another growth spurt. You will probably have put on some weight over the past few weeks too.

What's happening in my body?

You may see a midwife around now, who will weigh you and discuss how you're getting on. You might get to hear your baby's heartbeat for the first time. You will also get the results of any blood tests that you had during your booking appointment.

You will probably have been offered a test for 3 infectious diseases: HIV, hepatitis B and syphilis. If an infection has been picked up, then your midwife or doctor will talk to you about the best ways to protect your health and reduce the risk of passing on the infection to your baby.

Your blood pressure will be checked and you will need to provide a urine sample. This will be checked for signs of protein that could show if you're at risk of developing a dangerous condition called pre-eclampsia.


Constipation is common in early pregnancy. It's when you find it really hard to poo, it can make you feel bloated, sick and give you tummy ache.

Try to:

  • eat foods that are high in fibre, such as wholemeal bread, fruit and veg, beans and lentils
  • exercise regularly
  • drink lots of water
  • avoid iron supplements (but talk to your doctor or midwife before ditching any medication)

Read more about easing constipation in pregnancy on the NHS website.

Carbon monoxide alert

You can not see, smell or taste it – but carbon monoxide gas is a killer. You can come into contact with it through faulty or poorly ventilated cooking or heating appliances. If you've already got a carbon monoxide detector, then check that it's working.

There's usually a test button – if it does not beep, the battery may need replacing or you need a new detector. You can pick one up at most supermarkets.

You can also become exposed to this harmful gas through breathing in cigarette smoke.

2nd trimester pregnancy symptoms (at 16 weeks)

Everyone's pregnancy is different but if you feel unwell and it's getting you down, speak to your doctor or midwife.

Your pregnancy symptoms may include:

You may also experience symptoms from earlier weeks, such as:

Read Tommy's guide to common pregnancy symptoms.

What does my baby look like?

Your baby, or foetus, is around 11.6cm long from head to bottom, which is the size of an avocado. The weight is around 100g, which is the same as a medium bag of salad.

Your baby is starting to pull faces now, but any smiling or frowning will be completely random, as there's no muscle control yet. The nervous system continues to develop, and this enables your baby to start moving their arms and legs. Your baby's hands can form fists and they may start punching around inside you too. You might be able to feel your baby kicking from week 17 onwards.

Action stations

Many women will tell their employer after they've had their first pregnancy scan at around 12 weeks. Once you tell your employer, you have maternity rights and can attend antenatal appointments during paid work time. You can also ask for a risk assessment of your workplace to ensure that you're working in a safe environment.

It's a good time to tone up your pelvic floor muscles. Gentle exercises can help to prevent leakage when you laugh, sneeze or cough. Get the muscles going by pretending that you're having a wee and then stopping the 'urine' midflow. Visit Tommy's for more ideas about pelvic floor exercises.

Ask your midwife or doctor about online antenatal classes – they may be able to recommend one. The charity Tommy's has lots of useful information on antenatal classes and preparing you for birth.

Even if you've had children before, they're still worth going to as you can meet other parents-to-be. The NCT offers online antenatal classes with small groups of people that live locally to you.

Do your best to stop smoking, give up alcohol and go easy on the tea, coffee and anything else with caffeine. Ask your midwife or GP for support if you need it.

To keep bones and muscles healthy, we need vitamin D. From late March/early April to the end of September, most people make enough vitamin D from sunlight on their skin. However, between October and early March, you should consider taking a daily vitamin D supplement because we cannot make enough from sunlight.

Some people should take a vitamin D supplement all year round, find out if this applies to you on the NHS website. You just need 10 micrograms (it's the same for grown-ups and kids). Check if you're entitled to free vitamins.

It's recommended that you do 150 minutes of exercise a week while pregnant. You could start off with just 10 minutes of daily exercise - perhaps take a brisk walk outside. Check out Sport England's #StayInWorkOut online exercises (scroll to the pregnancy section). Listen to your body and do what feels right for you.

There's no need to eat for 2. You don't need any extra calories until the third trimester, which starts in week 28. Try to eat healthily, with plenty of fresh fruit and veg, and avoid processed, fatty and salty foods. You may be able to get free milk, fruit and veg through the Healthy Start scheme.

You and your family should follow the government and NHS guidance on coronavirus (COVID-19):

  • read government guidance on how to stay safe from COVID-19
  • get NHS advice about COVID-19
  • use the NHS COVID-19 app for England and Wales – it's the fastest way of knowing when you've been exposed to COVID-19
  • To find out about about COVID-19 and pregnancy, childbirth and breastfeeding, have a look at advice on the:

  • NHS website
  • Breastfeeding Network
  • World Health Organization
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