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Pregnancy health centre

Antenatal appointments - Screening tests and checks during your pregnancy

NHS Choices Medical Reference

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Early in your pregnancy you will be offered a number of different tests. These include tests for you, such as blood tests to check for infections, and tests for your baby, known as screening tests, to assess whether your baby is at risk of developing certain abnormalities or conditions during pregnancy.

Screening tests do not diagnose these conditions but assess how likely it is that your baby will be born with them. If your baby is considered to be high risk, you may be offered further diagnostic tests.

Screening tests can reassure you that your baby is likely to be born healthy, but can also prepare you if there is a chance your baby will be born with special needs. You do not have to have any screening tests if you do not wish to, although they can help your antenatal care team to provide the best care and support for you and your baby throughout your pregnancy.

All tests are done to help make your pregnancy safer or to check that your baby is healthy, but you should always make sure you are clear about why they are being done. Talk to your midwife or doctor so you understand why a test is being offered so you can make an informed choice about whether you want the test.

Tests and checks you may be offered are outlined below:

Urine tests

You will be asked to give a sample of urine at all of your antenatal appointments. This is checked for protein, also called albumin. Protein in your urine can be an indication of an infection or pregnancy-induced hypertension (high blood pressure), which can be a sign of pre-eclampsia.

Blood pressure

Your blood pressure will be checked at each antenatal appointment. A rise in blood pressure later in pregnancy could be a sign of pre-eclampsia (see below).

It is very common for your blood pressure to be lower in the middle of your pregnancy than at other times. This is not a problem, but may make you feel light-headed if you get up quickly.

Ultrasound scans

An ultrasound scan uses sound waves to build up a picture of your baby in the womb. It is completely painless, has no known side-effects and can be carried out at any stage of pregnancy.

An ultrasound scan can be used to:

  • check a baby's measurement and give a good idea of a baby's age and when it is likely to be due,
  • check if you are having more than one baby,
  • detect abnormalities in the baby, especially of the neck and spine,
  • show the position of the baby and placenta,
  • check that the baby is growing and developing normally.

You should be offered an ultrasound scan between eight and 14 weeks of pregnancy to estimate when your baby is due and check whether you are expecting more than one baby. This scan may also be part of your screening test for Down's syndrome.

You may be asked to drink a lot of fluid before you have this ultrasound scan, as this fills your bladder and pushes up your womb to give a better picture.

You should be offered another scan between 18 and 20 weeks, known as the anomaly scan. This scan checks for the physical physical development of your baby. Remember, the main purpose of this scan is to check that there are no structural abnormalities. Your midwife or doctor should provide information on this scan and what the results may mean for you.

Screening for Down's syndrome

Down's syndrome is a condition caused by the presence of an abnormal number of chromosomes in a baby's cells  All pregnant women are offered screening for Down's syndrome. Different maternity services may use different tests, but all tests carried out in the NHS will meet national standards. 

Combined screening

This involves a blood test and an ultrasound scan. Either during your dating scan, or at an additional appointment between eight and 14 weeks, nuchal translucency may be checked. Studies have shown that the thickness of the nuchal pad, the area between the skin and the soft tissue at the back of a baby's neck, is related to the risk of Down's syndrome. As well as this you will have a blood test that measures two blood chemicals associated with pregnancy. The information from your scan and blood test can be used to estimate the risk of your baby having Down's syndrome.

Serum screening

This test measures three or four chemicals in your blood associated with pregnancy. The measurements can work out the risk of your baby suffering from Down's syndrome. This test is usually done between 15 and 20 weeks of pregnancy.

Testing for infections

Your midwife or doctor will offer you a number of tests that check for certain infections that can cause problems in pregnancy if left undetected. These include:

  • Asymptomatic bacteriuria - a bladder infection that has no symptoms. Treating it reduces your risk of developing a kidney infection. It is detected using a urine test.
  • Hepatitis B - a potentially serious infection that can affect your liver. A mother can pass it to her unborn baby through blood and body fluids. Hep B can be detected through a blood test and a baby can be vaccinated at birth to prevent the infection from developing.
  • HIV - although HIV usually causes no symptoms at first, it can lead to AIDS. HIV can be passed from a mother to her unborn baby but the risks to the baby can be reduced if the mother is diagnosed before giving birth. HIV is diagnosed through a blood test. If you are pregnant and diagnosed with HIV you should receive specialist care and support throughout your pregnancy.
  • Rubella (German measles) - you will be offered screening to check your immunity to the rubella virus. If you are not immune you can choose to be vaccinated after you have given birth. It is not safe to be vaccinated for rubella while you are pregnant.
  • Syphilis - sexually transmitted infection that can be passed from an infected mother to her unborn baby and may cause miscarriage, stillbirth or abnormality. It is rare in the UK. A person with syphilis may not show any symptoms for many years. Syphilis is diagnosed through a blood test. Mother and baby can be successfully treated if the infection is detected early.

Anaemia test

Anaemia makes you tired and less able to cope with loss of blood when you give birth. You will be offered two blood tests for anaemia, one at your booking appointment and one at around 28 weeks. If you are found to be anaemic, you will probably be offered iron and folic acidsupplements.

Blood group and Rhesus D status

Early in your pregnancy you will be tested to check your blood group and whether you are rhesus negative or positive.

People who are rhesus positive have a substance called D antigen on the surface of their red blood cells; people who are rhesus negative do not. If you are rhesus negative and your partner is rhesus positive your baby may be positive. This is not usually a problem in your first pregnancy, but may affect your next baby if you become pregnant again.

This is because after your first birth, some of your (rhesus positive) baby's blood may have entered your own bloodstream, causing you to produce antibodies. This is known as becoming 'sensitised'. If you carry a rhesus positive baby again those antibodies will still be present and your immune response will be quicker and greater. These antibodies can cross the placenta and attach to the D antigen on your baby's red blood cells. This can be harmful to your baby and cause a condition known as haemolytic disease of the new born, which can lead to anaemia and jaundice.

If you are rhesus D negative you will be offered anti-D injections to prevent any problems if you have more children. Your midwife or doctor will explain the implications of being rhesus D negative and what the anti-D injections do. For more information you can also go to our topic page on rhesus factor disease.

Tests for thalassaemia and sickle cell disease

Blood tests are also used to screen for inherited blood conditions such as thalassaemia and sickle cell disease. These diseases affect haemoglobin, the part of blood that carries oxygen around the body, and mainly affect people whose family origin is from outside Northern Europe (for example someone who is Italian, Maltese, Portugese, Spanish, Indian, Chinese, African or Afro-Caribbean).

In your early appointments your midwife or GP will give you information on these conditions and may ask you some questions about you and your partner's family origins. All women are offered a blood test to screen for thalassaemia and Sickle disease and those considered at risk will be offered a specific blood test

The screening process will determine whether you are at risk of being a carrier of one of these conditions, and if your baby may be at risk of being born with one of the conditions. If you are found to be a carrier of an inherited blood condition then the father of your baby will also be offered screening, along with advice and support.

Gestational diabetes

Gestational diabetes is a type of diabetes that can develop in the later stages in pregnancy. Some women during pregnancy do not produce enough insulin to absorb the high levels of glucose (sugar) in their blood. You are more at risk of gestational diabetes if:

  • you are overweight (BMI of 30kg/m2 or above)
  • you have given birth to a large baby before (4.5kg or more),
  • you have a close family member with diabetes,
  • you have had diabetes before, or
  • your family origins are South Asian, black Caribbean or Middle Eastern.

Gestational diabetes can be controlled with changes in diet and exercise or with insulin if lifestyle measures are not effective. You will be closely monitored if you have gestational diabetes or are thought to be at risk.

If left untreated, you may be at risk of a miscarriage or your baby may grow to be larger than normal which can lead to difficulties during birth. Also, your baby may be at risk of dying during birth, health problems following birth and developing obesity and/or diabetes in later life.

For more information on gestational diabetes see the NICE guidance of diabetes in pregnancy.

Pre-eclampsia

Pre-eclampsia is a condition that can occur when there is a problem with the placenta, the organ that links your baby's blood supply to yours. The cause is not fully understood. However, it is thought that a problem may develop with the blood vessels in the placenta. It affects one in 10 pregnancies and can cause growth problems in your unborn baby.

Symptoms of pre-eclampsia include:

  • headaches,
  • blurred vision, and
  • flashing lights

Signs of pre-eclampsia include:

  • high blood pressure,
  • protein in the urine, and
  • swelling of the hands, feet, ankles and sometimes face.

Your blood pressure and urine will be checked at every antenatal appointment to check for signs of pre-eclampsia. You may have to have your blood pressure checked more often if you show other signs of pre-eclampsia, such as protein in your urine.

You are more at risk of pre-eclampsia when you are pregnant and:

  • you are aged 40 or over,
  • you have not had a baby before,
  • your last pregnancy was more than 10 years ago,
  • you or a family member have had pre-eclampsia before,
  • your body mass index is 35kg/m2 or more,
  • you have circulatory problems such as high blood pressure,
  • you have kidney disease, or
  • you are expecting more than one baby.

Placenta praevia (low-lying placenta)

Placenta praevia is when the placenta is attached to the lower part of the uterus and covers all or part of the entrance to the womb (cervix).

If in your anomaly scan (at 18-20 weeks) your placenta appears to extend over your cervix, you will be offered another scan between 32-36 weeks to check the position of the placenta again. Usually, as your womb grows the placenta moves up with it so it is in the correct position for birth and does not cause any problems.

If the placenta remains low or covering the cervix then it is not safe to have a vaginal birth and you will need a caesarean section. For more information see the caesarean sections topic.

Medical Review: February 25, 2010
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