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Pregnancy and baby

Antenatal checks and tests

What will happen to my body during pregnancy?

Media last reviewed: 20/03/2017

Next review due: 20/03/2020

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 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 body mass index (BMI). 

Women who are overweight for their height are at increased risk of problems during pregnancy.

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 because the baby is growing, but your body also stores fat for making breast milk after the birth. 

It's important to eat the right foods and do regular exercise during your pregnancy.

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 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 fits (seizures). 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 check 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:

  • screening for HIV, syphilis and hepatitis B
  • blood group
  • rhesus disease
  • anaemia
  • diabetes

Screening for HIV, syphilis and hepatitis B

You'll be offered a blood test for three infectious diseases: HIV, hepatitis B and syphilis. This is usually offered at an appointment with a midwife when you are around 8-12 weeks pregnant.

The tests are recommended to protect your health through early treatment and care, and reduce any risk of passing on an infection to your baby, partner, or other family members.

Read more about screening for HIV, syphilis and hepatitis B.

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 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 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 southeast 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.

Page last reviewed: 08/01/2015

Next review due: 31/10/2017


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Midwife checking pregnant woman's bump

Your antenatal appointments

Find out when your antenatal appointments will happen, and what to expect

Ultrasound scans

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Infections in pregnancy

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Services near you

Get help with all aspects of your pregnancy from the NHS in your area