Whether you're indifferent to needles or go faint at the sight of them, as a pregnant woman you will need to have blood taken at least once during your pregnancy. When you first start your antenatal care at your surgery, what's known as your booking in appointment, your midwife or doctor will take some blood to run tests on so that they can find out key information about your health that's relevant to your pregnancy. After that you may need to have other blood tests taken if your doctor thinks that they are necessary, or if you yourself want to screen for developmental abnormalities or possible infections.

Whenever you have blood taken it is drawn from your arm with a needle in a quick and painless procedure: you shouldn't feel more than a light prick and very slight discomfort from the needle, but you might want to look away if you don't like needles or the sight of blood. The following are the tests that are most commonly needed or offered.

Booking in tests
These are the tests that are usually carried out when you first book in with your doctor:

  • Blood group - In the event of you needing a blood transfusion at some point during pregnancy or labour, it will help doctors to know what blood group you are to match your blood. You might be O (most common), A, B or AB.

  • Rhesus (Rh) factor - Most people are Rh positive, meaning that they carry a protein on their red blood cells. People whose red blood cells don't carry this protein are rhesus negative. For your everyday health your rhesus factor isn't important, but it is significant during pregnancy if you are rhesus negative. If you are rhesus negative but your baby is rhesus positive (due to the father) then you will need injections to protect your baby's health. This is because, as a Rhesus negative blood carrier, if your blood has been exposed to rhesus positive blood your body may have started producing antibodies to destroy the rhesus positive blood cells - this may lead to anaemia, jaundice or sometimes more serious complications for your baby if s/he is rhesus positive. As you can never be sure whether you've been exposed to rhesus positive blood before (eg. with a previous pregnancy) the doctor will assume both that you have been exposed to Rh positive blood, and that the baby's blood is Rh positive and treat you accordingly.

    The usual treatment for a pregnant Rh negative woman is injections of anti-D immunoglobulin (anti-D) at 28 and 34 weeks to prevent your body from producing antibodies against your baby's blood cells.

  • Rubella (German Measles) - Testing for Rubella in early pregnancy is routine because of the very high risk to the baby if the disease is contracted in early pregnancy. Because the chances are high that you will either have received a vaccine against rubella or caught the disease as a child, most women of child-bearing age are immune. If you are shown to be immune you need not worry. However, if the test shows that you do not have immunity then you will be advised to be particularly careful about possible exposure to the disease and if you do contract the disease in the first trimester of pregnancy you will receive counselling about a possible termination.

  • Haemoglobin (iron) levels - Low iron and anaemia are quite common during pregnancy as your body needs to dramatically increase the amount of blood in your blood supply. If you aren't getting enough iron then your blood is less able to carry oxygen to all your organs and you may suffer from anaemia leaving you feeling tired, washed out, breathless, dizzy, headachy and with a loss of appetite. The blood test will show whether your iron intake is something that you need to be concerned about, upping your intake through dietary means and perhaps a supplement. Your iron levels are usually tested again as you enter the third trimester, and your doctor may want to do a blood test at other times in your pregnancy if you are particularly tired and low on energy.

  • Hepatitis B - Hepatitis B is a disease where a virus attacks the liver. As you may carry the virus without knowing it, and as it can pass to your baby through the placenta causing serious liver damage after birth, screening for Hepatitis B is routine for pregnant women. If you are shown to have had an infection during pregnancy then your baby will be treated soon after birth to protect the liver.

  • Syphilis - While syphilis is now quite a rare disease, it can cause serious developmental abnormalities for unborn babies if left untreated in pregnant women and is easily treated, so doctors usually prefer to test pregnant women just in case.

  • HIV - An HIV test is routinely offered to pregnant women, but your doctor needs your consent to carry out the test, so you can reject the test if you prefer. If you think there's a possibility that you may have been exposed to the virus and you are not offered the test then you can ask for one to be carried out. If you are HIV positive then your antenatal care, birth and baby feeding can all be tailored to minimise the chances of you passing the infection on to your baby, so it's well worth being sure about your status if you have cause for concern.

Other tests
Toxoplasmosis - Toxoplasmosis is an infection most often picked up from raw or undercooked meat, but it is also found in the faeces of infected cats. Toxoplasmosis infection in a pregnant woman is rare, but it is potentially damaging to the fetus and is more dangerous the earlier in the pregnancy it is contracted. Pregnant women in the UK are not routinely screened for toxoplasmosis immunity, but if you think that you are at particular risk of an infection then you can ask your doctor for a blood test that can be carried out with your booking in tests. If you don't know whether you are immune to toxoplasmosis from a previous infection then you should be particularly careful when handling raw meat, make sure all meat is fully cooked through, and be careful to wash your hands well after coming in contact with soil. If you have a cat then it's best to leave changing the cat litter to someone else.

The double and triple tests - Blood tests to screen for developmental abnormalities are offered between weeks 16 and 18 of pregnancy. Different tests can be carried out to measure the levels of various hormones and proteins in the blood to offer some indication of the risk of certain conditions such as spina bifida and Down's syndrome. To screen for only spina bifida a blood test looks for high levels of alphafeto protein in the blood, which may also be an indicator for Down's syndrome. However, it's usual to combine this test with at least one other test, for the hormone human chorionic gonadotrophin (HCG), as both of these together provide a more accurate indicator for Down's. This is the double test. If the level of oestriol in the blood is also tested then the test is called the triple test. If you are thought to be at very high risk of Down's syndrome a fourth measure, for the amount of inhibin A in the blood is also taken at the same time, which is the quadruple test.

These blood tests will not tell you whether your baby definitely has an abnormality, but they do offer some indication of your level of risk. If the tests show that you are at high risk then you will be offered an amniocentesis, which is a far more accurate but not entirely risk-free test.

Glucose tolerance / blood sugar tests - The glucose tolerance test checks for gestational diabetes and is usually carried out if you are considered at higher risk of developing the condition (perhaps due to your age or weight), or if a routine urine test has shown that you have glucose in your urine and so may have gestational diabetes.

Gestational diabetes occurs when your body is not able to produce the extra insulin that your body requires during pregnancy in order to regulate your blood sugar levels. Women with gestational diabetes may have particularly large babies and so need to deliver by c-section. The condition usually clears up after pregnancy, but you are at a much higher risk of developing diabetes proper if you have had gestational diabetes.

To test for gestational diabetes you will need to give several blood samples at intervals. Before going to the clinic you'll be required to neither eat nor drink anything other than water for 6 hours and when you arrive a sample of your blood will be taken as a control sample to measure the level of sugar in your blood when you haven't eaten. You will then be given a very sweet drink to drink and more blood taken for testing at intervals to see how your blood sugar level changes. As this test can take several hours it might be an idea to take along a good book or some other diversion for the waiting room.

If you are diagnosed with gestational diabetes then it is usually controllable with a special diet, however, some women will need insulin injections. You will usually need to attend more antenatal appointments than usual to have the condition monitored.

Occasional tests - During the course of your antenatal care your doctor may want to conduct blood tests at any time if there is reason to believe that something isn't as it should be. One of the most common reasons for taking more blood tests is to check on your iron levels if you are particularly fatigued or displaying other symptoms of anaemia. Because your doctor may need you to take a blood test at any time during pregnancy, it's very important that you attend all your antenatal appointments.