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Pregnancy and baby

Antenatal checks and tests

What will happen to my body during pregnancy?

Media last reviewed: 20/03/2014

Next review due: 20/03/2016

During your pregnancy, you'll be offered a range of tests, including blood tests and ultrasound baby scans. These tests are designed to help make your pregnancy safer, check and assess the development and wellbeing of you and your baby, and screen for particular conditions.

You don't have to have any of the tests. However, it's important to understand the purpose of all tests so that you can make an informed decision about whether to have them. Discuss this with your maternity team.   

Weight and height checks in pregnancy

You will be weighed at your booking appointment, but you won't be weighed regularly during your pregnancy. Your height and weight are used to calculate your BMI (body mass index). Women who are overweight for their height are at increased risk of problems during pregnancy you can find out more about being overweight when you get pregnant.

Most women put on 10-12.5kg (22-28lb) in pregnancy, most of it after they are 20 weeks pregnant. Much of the extra weight is due to the baby growing, but your body also stores fat for making breast milk after the birth. During your pregnancy, it's important to eat the right foods and do regular exercise.

Antenatal urine tests

You'll be asked to give a urine sample at your antenatal appointments. Your urine is checked for several things, including protein or albumin. If this is found in your urine, it may mean that you have an infection that needs to be treated. It may also be a sign of pre-eclampsia.

Pre-eclampsia affects 5% of pregnancies and can lead to a variety of problems, including seizures (fits). If left untreated it can be life threatening. Pre-eclampsia can also affect the growth and health of the baby. Women with the condition usually feel perfectly well.

Blood pressure tests in pregancy

Your blood pressure will be taken at every antenatal visit. A rise in blood pressure later in pregnancy could be a sign of pregnancy-induced hypertension. It's very common for your blood pressure to be lower in the middle of your pregnancy than at other times. This isn't a problem, but it may make you feel lightheaded if you get up quickly. Talk to your midwife if you're concerned about it. Find out more about high blood pressure and pregnancy.

Blood tests in pregnancy

As part of your antenatal care you'll be offered several blood tests. Some are offered to all women, and some are only offered if you might be at risk of a particular infection or condition. All the tests are done to make your pregnancy safer or to check that the baby is healthy, but you don't have to have them if you don't want to.

Talk to your midwife or doctor and give yourself enough time to make your decision. They will also give you written information about the tests. Below is an outline of all the tests that can be offered. 

The blood tests you may be offered include:

  • blood group
  • rhesus disease
  • anaemia
  • diabetes

Blood group

It is useful to know your blood group in case you need to be given blood, for example if you have heavy bleeding (haemorrhage) during pregnancy or birth. The test tells you whether you are blood group rhesus negative or rhesus positive. Women who are rhesus negative may need extra care to reduce the risk of rhesus disease.

Rhesus disease

People who are rhesus positive have a substance known as D antigen on the surface of their red blood cells. Rhesus negative people do not. A rhesus negative woman can carry a baby who is rhesus positive if the baby's father is rhesus positive. If a small amount of the baby's blood enters the mother's bloodstream during pregnancy or birth, the mother can produce antibodies against the rhesus positive cells (known as anti-D antibodies).

This usually doesn't affect the current pregnancy, but if the woman has another pregnancy with a rhesus positive baby, her immune reponse will be greater and she may produce a lot more antibodies. These antibodies can cross the placenta and destroy the baby's blood cells, leading to a condition called rhesus disease, or haemolytic disease of the newborn. This can lead to anaemia and jaundice in the baby. Find out more about rhesus disease.

Anti-D injections can prevent rhesus negative women from producing antibodies against the baby. Rhesus negative mothers who haven't developed antibodies are therefore offered anti-D injections at 28 and 34 weeks of pregnancy, as well as after the birth of their baby. This is quite safe for both the mother and the baby.  


Anaemia makes you tired and less able to cope with loss of blood when you give birth. If tests show that you're anaemic, you'll probably be given iron and folic acid. 


You may be at higher risk of developing diabetes in pregnancy (gestational diabetes) if you are overweight, you've had diabetes in pregnancy before, you have a close relative with diabetes or you're of south east Asian, black Caribbean or Middle Eastern origin.

If you're considered to be high risk for gestational diabetes, you may be offered tests in pregnancy including blood tests.

Read more about gestational diabetes.

Blood tests for infections in pregnancy

You'll be offered blood tests for:

  • Susceptibility to rubella (german measles) – if you get rubella in early pregnancy, it can seriously damage your unborn baby. Your midwife or doctor will talk to you about what happens if your test results show low or no immunity.   
  • Syphilis – you'll be tested for this sexually transmitted infection as it can lead to miscarriage and stillbirth if left untreated.
  • Hepatitis B – this virus can cause serious liver disease, and it may infect your baby if you're a carrier or you're infected during pregnancy. Your baby won't usually be ill but has a high chance of developing long-term infection and serious liver disease later in life. Your baby can be immunised at birth to prevent infection. If you have hepatitis B, you'll be referred to a specialist.
  • Hepatitis C – this virus can cause serious liver disease and there is a small risk it will pass to your baby if you are infected. It can't be prevented at present. Tests for hepatitis C aren't usually offered routinely as part of antenatal care. If you think you might be at risk, talk to your midwife or GP, who can arrange a test. If you're infected, you'll be referred to a specialist and your baby can be tested after it's born.
  • HIV (human immunodeficiency virus) – this is the virus that causes AIDS. HIV infection can be passed to a baby during pregnancy, at delivery or after birth by breastfeeding. As part of your routine antenatal care, you'll be offered a confidential test for HIV infection. If you're HIV positive, both you and your baby can have treatment and care that reduces the risk of your baby becoming infected.  

Be aware that you can still catch all these infections during pregnancy after you've had a negative test result. This includes sexually transmitted infections such as syphilis, HIV and hepatitis B if you or your sexual partner take risks, such as having unprotected sex. You can also get HIV and hepatitis if you inject drugs and share needles. Your midwife or doctor can discuss this with you.

Find out more about screening for infectious diseases in pregnancy and potentially harmful infections in pregnancy.

HIV infection in pregnancy

If you think that you're at risk of getting HIV or you know that you're HIV positive, talk to your midwife or doctor about HIV testing and counselling. You can also get free confidential advice from the Sexual Health Line on 0300 123 7123, or you can talk confidentially to someone at Positively UK on 020 7713 0222.

If you're HIV positive, your doctor will need to discuss the management of your pregnancy and delivery with you. 

There is a one-in-four chance of your baby being infected if you and your baby don't have treatment. Treatment can significantly reduce the risk of transmitting HIV from you to your baby. One in five HIV-infected babies develop AIDS or die within the first year of life, so it's important to reduce the risk of transmission.

Your labour will be managed in order to reduce the risk of infection to your baby. This may include an elective caesarean delivery.

Your baby will be tested for HIV at birth and at intervals for up to two years. If your baby is found to be infected with HIV, paediatricians can anticipate certain illnesses that occur in infected babies and treat them early. All babies born to HIV positive mothers will appear to be HIV positive at birth, because they have antibodies from their mother's infection. If the baby is not HIV positive, the test will later become negative because the antibodies will disappear.

You'll be advised not to breastfeed as HIV can be transmitted to your baby in this way.

Page last reviewed: 08/01/2015

Next review due: 08/01/2017


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Ultrasound scans

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Infections in pregnancy

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