Tests and screening

During your pregnancy, you’ll be offered a range of tests, including blood tests and ultrasound baby scans. These are designed to help make your pregnancy safer, check and assess the development and the 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 their purpose so that you can make an informed decision about whether to have them. Our Maternity team (your midwife, radiographer or obstetrician) will be able to give you more information and answer any questions you may have as well as give you written information about our screening tests.

If you are not sure why you might have been asked to come in for a screening test you can find out more on our dedicated page.

Weight and height

Your height and weight are used to calculate your BMI (body mass index). Most women put on 10-12.5kg (22-28lb) during 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. It's really important that you eat the right foods and exercise regularly as women who are overweight are at increased risk of problems during pregnancy.

Please be assured that you will not be asked to be weighed regularly during your pregnancy, unless you have diabetes or a high BMI.


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 or pregnancy-related condition, such as pre-eclampsia.

Blood pressure

Your blood pressure will be taken at every antenatal visit, as 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 can make you feel lightheaded if you get up a little too quickly. If you're concerned, please talk to your midwife.

Blood tests

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 inherited condition. All the tests are done to make your pregnancy safer or to check that the baby is healthy.

Blood group

It is really important that we know your group in case you need to be given blood, for example if you have heavy bleeding (haemorrhage) during pregnancy or birth. The test also tells you whether you are 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 while rhesus negative people do not. A rhesus negative woman can carry a baby who is rhesus positive. If a small amount of the baby’s blood enters the woman’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 response will be greater and she may produce a lot more antibodies. These antibodies can cross the placenta and affect the baby’s red blood cells, leading to anaemia in the baby during pregnancy or following birth.

Anti-D injections can prevent rhesus negative women from producing antibodies against the baby and they are offered to rhesus negative women who haven’t developed antibodies at 28 weeks of pregnancy, as well as after the birth of their baby.

Anaemia (iron deficiency)

Anaemia is due to a lack of iron can make you feel tired. If tests show that you’re anaemic, you'll be offered iron and folic acid which will help to improve your blood count in preparation for birth.