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This article waslast modified on 5 November 2020.

Pregnancy is the period of time when a foetus develops inside a woman's uterus and ends with the birth of the infant. The following sections contain information on some tests related to pregnancy that may be performed to establish if they are pregnant, to diagnose existing problems or to screen for potential problems. For further information about all aspects of pregnancy please refer to the NHS Choices website.

Newborn screening policy varies within the NHS. Tests are performed to detect infants with metabolic illness, and genetic abnormalities, and, if applicable, to determine the mother's need for Rh immune globulin. These may include screening tests as described in the Screening Tests for Newborns.

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Pre-Conception and First Trimester Tests
  • Overview

    Pre-Conception (Pre-Pregnancy) and First Trimester (up to 12 weeks)

    If you are considering having a child then arrange a consultation with a healthcare professional who, based on family and medical histories, will be able to recommend which laboratory tests should be performed. The preferred tests used at this time will vary, but may include the following.

  • Pregnancy test

    Shortly after conception, Human Chorionic Gonadotropin (hCG) hormone is produced by the developing placenta and after two weeks can be detected in urine and blood.

    A negative pregnancy test indicates either there is no pregnancy, or the amount of hCG is not yet sufficient to be detected. If the test is positive, it confirms the pregnancy. The amount of hCG produced during pregnancy doubles every two to three days, and levels off in the second or third month. If pregnancy is still suspected despite a negative urine test, the test can be repeated after two-three days. Home pregnancy tests that detect hCG in urine are widely available in supermarkets and chemists.

    Related Tests: hCG

  • Immunity to Rubella (German Measles)

    Rubella is caused by a virus that is passed from person-to-person by coughs or sneezes. Women, who have either had the rubella virus infection or have received the vaccination, produce an antibody (protein made in response to a foreign substance introduced into the body) in their blood that will usually prevent them from getting the infection a second time. This antibody also protects the unborn baby against the virus; this protection is called immunity.

    Rubella infections during childhood usually cause mild symptoms. However, if a woman becomes infected with rubella virus during the first three months of her pregnancy and does not have immunity to the virus, the baby is at risk of having serious birth defects or dying.

    All women considering a first time pregnancy, or those who are pregnant for the first time, should be tested to see if they have this immunity. A blood specimen is tested to see if a sufficient amount of antibody is present in the blood to protect the mother and the baby. If a woman does not have enough antibodies, she may be given a rubella virus vaccination which will, in most cases, cause her to produce these protective antibodies.

    Related Tests: Rubella

  • Human Immunodeficiency Virus (HIV)

    HIV is the virus that causes AIDS (Acquired Immunodeficiency Syndrome). At least 90-95% of individuals who are infected with HIV will, within three months of exposure, develop enough antibodies to have a positive HIV antibody test; over 99% of HIV infected individuals will have a positive test within six months. If the woman has the virus, it can be passed to, and infect the baby.

    The HIV test detects antibodies to HIV in the blood. Although, a positive HIV antibody test could mean a woman may be infected with HIV, the test result may be non-specific and may be positive for other reasons. The laboratory will automatically perform additional confirmatory HIV tests to determine conclusively if she really has HIV infection (or not). If the confirmatory tests indicate HIV infection, it does not mean the individual has developed AIDS. 

    A negative test for the antibody to HIV means either there is no infection, or a sufficient amount of the antibody has not yet been produced to be detected. If a woman participates in high risk activities that may transmit HIV, such as unprotected sexual contact or intravenous drug use, it is recommended that she be retested later.

    Related Tests: HIV antibody test

  • Hepatitis B Screening

    Infection with hepatitis B virus causes an inflammation of the liver. If left untreated, this disease can develop into liver cancer or cause death. It is recommended that a woman who is thinking of becoming pregnant, or who is already pregnant, has a simple blood test for hepatitis B virus. If the disease is detected before pregnancy, the woman can be treated so that a future baby is not at risk for infection. If already pregnant when the infection is detected, treatment should start, and the baby would receive treatment at birth to make sure the disease does not develop. A negative test for the virus means either there is no current infection, or there is not yet a sufficient amount of the marker to be detected. If a woman participates in high risk activities that may transmit hepatitis B virus, such as unprotected sexual contact or intravenous drug use, it is recommended that she be retested later.

    Related Tests: Hepatitis B

  • Syphilis

    Like HIV there is routine screening for syphilis in pregnancy. In addition depending on circumstances women may also be offered testing for Gonorrhoea (GC) and Chlamydia. If you have any concerns this should be discussed with your midwife, who will advise you accordingly. All these sexual transmitted diseases are caused by bacterial infections and can lead to a miscarriage, or infect the baby prior to, or during delivery.

    In the UK pregnant women are routinely tested for syphilis at the time of the first antenatal visit. A positive test usually means the individual has been infected in the past or is currently infected. A negative test result usually means the woman is not currently infected, however, it is possible that an infection is too new to detect. If you are concerned about other STDs and think you might be at risk, you should discuss this with your doctor or midwife.

    Related Tests: Gonorrhoea, Chlamydia, Syphilis

  • Haemoglobin

    Haemoglobin is the protein in red blood cells that gives blood its red colour. Its most important function is to carry oxygen from the lungs to the rest of the body. Haemoglobin is vital to life, and must remain at a healthy level for body organs to work properly. During pregnancy, the haemoglobin also provides oxygen to the unborn baby.  Anaemia is the term used when the amount of haemoglobin in the blood is too low to supply sufficient oxygen to the body. It is not unusual for pregnant women to have slightly low levels of haemoglobin, and this sometimes requires treatment with iron tablets.

    Related Tests: Haemoglobin

  • Haemoglobin Abnormalities Screen (Haemoglobinopathies)

    All pregnant women in the UK are offered screening for thalassaemias and those considered at high risk are also offered screening for sickle cell disease. If either of the test results are positive, your baby's father will also be offered a test, and you will be asked fill out a questionnaire to establish if you or your partner have a family history for these disorders. This helps identify couples at risk of passing on thalassaemia or sickle cell disease

    In addition a newborn blood spot screening programme for sickle cell disease has been introduced. This is done as part of the routine heelprick blood spot testing procedure for a number of disorders which takes place at 5-8 days of age.

    Further information can be found at NHS Choices website.

  • Blood Type and Antibody Screen

    Blood types are either A, B, AB, or O, and Rhesus (Rh) positive or negative. Both the mother and baby may experience problems if their blood types are different, or if the mother has antibodies that will react with factors on the baby’s blood cells. The best known example is when an Rh-negative woman is pregnant with an Rh-positive baby. The woman’s immune system can develop an antibody that reacts with the Rh-positive factor on her baby’s blood. The mother’s immune system does not usually come into contact with the baby’s blood until labour, so it is unusual for her first Rh-positive baby to become ill. The antibodies produced during that first pregnancy may cause problems in a future Rh-positive pregnancy, however.

    To greatly reduce the likelihood that an Rh-negative mother will develop this antibody, she may be given an injection of ‘anti-D gamma globulin’ at approximately 28 and 34weeks gestation, as well as shortly after the birth of a Rh-positive baby. Additional injections may be necessary during the pregnancy if there is any reason to suspect that her blood may have come into contact with that of the Rh-positive baby (e.g amniocentesis, Chorionic Villous Sampling or an abdominal injury). The injection is of an antibody which mops up any antigen present from the baby’s blood cells, so preventing the mother’s immune system from reacting to it.

    In addition to Rh-negative women who have had an Rh-positive baby, any woman who has had a blood transfusion or had prior pregnancies, may produce an antibody to blood factors, other than Rh, that can potentially harm an unborn baby. An antibody screen, during the first trimester, is done to determine if potentially harmful antibodies are already present in the mother’s blood.

    Limitation of Antibody Screen
    An antibody may be present but in an amount too low to be detected. The baby’s blood may react with the antibody even if the test is negative. If the mother has received an injection of 'anti-D gamma globulin' within the previous six months, the antibody screen may produce a positive result.

  • Urine Culture and Sensitivity

    Bacterial infections of urine frequently cause symptoms that require the mother to seek treatment. It is also common for pregnant women to have bacteria in their urine without symptoms (asymptomatic bacteriuria). Women should be offered routine screening for asymptomatic bacteriuria by midstream urine culture early in pregnancy. Identification and treatment of asymptomatic bacteriuria reduces the risk of pyelonephritis (kidney infection).

    The diagnosis of urine infection is made when a sample of urine has been cultured (kept in conditions where any bacteria present are encouraged to grow), and bacteria have been identified. The sensitivity to antibiotics of any bacteria present can be assessed. Your doctor will then prescribe an antibiotic that has been shown to kill the particular bacteria present in your urine. After the antibiotic treatment has been completed, a new urine specimen may be needed to confirm the bacteria are no longer present.

    Limitations of Urine Culture 
    Improper cleaning of the area prior to collection of the urine specimen may result in a contaminated specimen. Harmful bacteria may be masked by an abundant presence of insignificant bacteria.

    Related Tests: Urinalysis

  • Screening for Down's syndrome-Maternal Screening

    For details, see the article Screening for Down's syndrome-Maternal Screening (incorporating chorionic villus sampling described below)

    Most pregnancies produce healthy babies however, in some cases there is a risk of a baby having a birth defect caused by a genetic abnormality.

    Chorionic Villus Sampling (CVS) is normally performed between the tenth and twelfth week after a woman’s last menstrual period. The test involves taking a sample of 'chorionic villi', which are found in the placenta, using a needle passed into the mother's womb. The placenta has the same genetic make-up (DNA) as the baby, and so the sample can be used to look for genetic abnormalities in the baby’s DNA.

    Complications Associated with CVS 
    There is a risk of miscarriage (approximately 1%) associated with the CVS procedure. An infection may develop.

    Limitation of Testing 
    Not all genetic disorders can be detected.

  • Chorionic Villus Sampling

    Most pregnancies produce healthy babies however, in some cases there is a risk of a baby having a birth defect caused by a genetic abnormality.

    Chorionic Villus Sampling (CVS) is normally performed between the tenth and twelfth week after a woman’s last menstrual period. The test involves taking a sample of 'chorionic villi', which are found in the placenta, using a needle passed into the mother's womb. The placenta has the same genetic make-up (DNA) as the baby, and so the sample can be used to look for genetic abnormalities in the baby’s DNA.

    Complications Associated with CVS 
    There is a risk of miscarriage (approximately 1%) associated with the CVS procedure. An infection may develop.

    Limitation of Testing 
    Not all genetic disorders can be detected.

  • Non-Invasive Prenatal Testing (NIPT)

    For information on this test, read the article on Non-Invasive Prenatal Testing (NIPT)

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Second and Third Trimester Tests
  • Overview

    At an antenatal visit, the expectant mother may be asked to give a urine specimen that will be screened for the presence of sugar and/or protein.

    Other tests performed during the second trimester provide information to evaluate both actual and potential medical problems in the baby. Testing during the third trimester period is primarily directed toward preparation for the birth of a healthy baby.

  • Oral Glucose Tolerance Test

    Based on number of criteria you may be asked to undergo an oral glucose tolerance test (OGTT) during your pregnancy. This test shows how your body utilises a known amount of glucose (sugar) which will be given to you as a drink. A high blood glucose concentration approximately 2 hours after taking the glucose suggests that you have gestational diabetes (diabetes in pregnancy). You will be given instructions to fast before the test, a blood sample will be taken and you will then be given a drink containing a known amount of glucose. Another blood sample is taken 2 hours later and the glucose concentration in the blood measured. For further information on gestational diabetes please refer to NHS Choices website.

  • Screening for Down's Syndrome - Maternal Screening

    It is now possible during the early stages of pregnancy to estimate the risk of a mother having a Down’s affected baby using a combination of biochemical tests and ultrasound measurements. These tests may also indicate the possibility of other chromosomal disorders, such as Edward’s syndrome (Trisomy 18) and Patau's syndrome (Trisomy 13). This type of screening provides an opportunity to assess the risk of these conditions being present without performing more invasive procedures such as chorionic villus sampling (CVS) or amniocentesis. Only those women whose screening results indicate that they are in a higher risk group are counselled and offered these further tests.

    Screening for Down’s syndrome should ideally be performed before 14 weeks and 2 days, but later screening is possible.

    An ultrasound scan is offered at about 11 to 13 weeks of pregnancy. This involves taking a measurement of the nuchal translucency (NT) which is the sonographic appearance of a collection of fluid under the skin behind the fetal neck in the first-trimester of pregnancy. This measurement maybe used on its own, or in combination with biochemical results from a blood test (performed on the mother), to calculate the risk of the baby having Down’s syndrome.

    This ‘combined test’, comprising nuchal translucency, beta-human chorionic gonadotrophin, and pregnancy-associated plasma protein-A (PAPP-A), should be offered to screen for Down’s syndrome between 11+2 weeks and 14+1 weeks of pregnancy . The results from these tests are used to calculate the chance of the pregnancy being affected by Down’s syndrome or another chromosome abnormality. For women who attend later in pregnancy, blood tests may be offered between 14+2 and 20 weeks (second trimester maternal serum screen). At this time during pregnancy the blood levels of alpha fetoprotein (AFP), human chorionic gonadotrophin (hCG), unconjugated oestriol (uE3) and Inhibin A (InhA) may be measured. This is commonly referred to as the quad or quadruple test because of the use of four markers.

    All the test results are interpreted based on the age of the mother, her weight and other factors such as family history and smoking, to assess the risk of the baby having a chromosomal abnormality. Only a small proportion of women with a result in the higher risk category for Down’s syndrome will have an affected baby.

    Limitations of screening
    Screening tests are not conclusive for the presence of a birth defect but indicate the possibility of a problem. Further tests must be performed to confirm the baby’s condition.

    Related Tests: Second trimester maternal serum screen, unconjugated estriol

  • Amniocentesis

    Amniocentesis is usually performed at or after 15 weeks gestation. It is recommended in women aged over 35, or where there is reason to suspect an increased risk of a particular genetic abnormality in their baby, no matter what the maternal age.

    Amniotic fluid is removed from the mother’s womb using a needle inserted through the lower abdomen. The fluid contains skin cells from the developing baby and these can be tested for chromosomal and other genetic abnormalities. It can take two or three weeks to grow the small number of cells obtained in order to provide enough DNA to perform the necessary tests.

    Complications Associated with Amniocentesis 
    There is a risk of miscarriage (approximately 1%) associated with the procedure. The procedure may cause an infection.

    Limitation of Testing 
    Not all genetic disorders can be detected.

  • Haemoglobin and Platelet Count

    All women lose a small amount of blood during delivery. Although this is usually not a problem, even a small blood loss can be harmful to women with anaemia. Your doctor may want to know the level of haemoglobin in your blood prior to delivery to assess the possible impact of the expected blood loss. (Refer to the First Trimester section for additional information).

    Platelets are cells found in blood that help form clots to stop bleeding. Women with low platelet counts, or who have platelets that don't function properly to form clots, are at risk of life-threatening bleeding during delivery. Follow-up testing may be needed to help determine treatment options if a platelet problem is detected.

    Related Tests: Haemoglobin, Platelet count