Screening tests in pregnancy
This blog is about screening tests in pregnancy. It is part of a series of blogs regarding your pregnancy and antenatal care. The first blog was about what to do when you find out you are pregnant.
You will be offered lots of screening tests in pregnancy. They are designed to detect any health problems that you may have and offer treatment if needed.
You may decline any tests or treatment in pregnancy. Your health professionals will ensure that you are fully informed about the tests or treatments that you wish to decline.
You should receive information about screening tests prior to your booking appointment. The blood tests that will be offered are –
Full blood count – It is common to have a low haemoglobin (Hb) in pregnancy so this test looks at your booking Hb. It also looks at your white cell count (which could show an infection) and your platelet levels as well as other markers in your blood. This test is repeated at 28 weeks to monitor your haemoglobin levels. If your iron level is low, you may require iron tablets.
Group and Save – This is to determine your blood group. If you have a Rhesus negative blood group, you will be offered an injection of Anti D at 28 weeks and after the birth of your baby. This is a blood product that stops your body from producing antibodies if your baby’s blood and your blood were to mix. Unless you know your partner’s blood group, the assumption will be that your baby is Rhesus positive; as it is the dominant blood group. You can decline Anti D if you know your partner is Rhesus negative. The baby’s blood group will be checked at birth. If your baby is Rhesus negative you won’t need Anti D. If your baby is Rhesus positive, the recommendation would be for you to have Anti D.
HIV – All women are offered HIV testing in pregnancy. There have been many advances in the treatment of HIV. Women who have low viral loads at the time of labour can aim for a normal delivery. Treating women during pregnancy can help to reduce the baby’s chance of contracting the virus.
Syphilis – This is a sexually transmitted disease that if left untreated can cause health problem in babies. Any women found to have syphilis can be treated with antibiotics to treat them and to protect their babies.
Hepatitis – Hepatitis is an infection of the liver. Women with hepatitis in pregnancy need careful monitoring. The baby will be treated after birth by a course of vaccinations.
Sickle cell disease (SCD) and thalassaemia major – These are inherited blood diseases. People who have these conditions will need specialist care throughout their lives. Anyone can carry the trait for these blood disorders and this doesn’t normally cause any problems. If you are found to be carrying the trait, your partner would be offered testing. If your partner also carried the trait, you would have a 1 in 4 chance of your baby having the full disease. In this case, you would be offered full counselling into the options open to you. It’s for this reason that the recommendation is for all women to have their booking bloods taken by 10 weeks of pregnancy.
Tests for diabetes – Depending on your family history, ethnic origin, body mass index (BMI) at booking, previous big babies or previous gestational diabetes, you may be offered screening for diabetes. This is usually done by a glucose tolerance test (GTT) but some hospitals may also offer you a fasting glucose test. The GTT requires you to fast for the first blood test, have a sugary drink then your blood is taken at one hour then two hour intervals after you finish the drink. There may other situations in pregnancy where you may be tested for diabetes, for example, if your baby was growing bigger then expected.
This scan is performed between 10 -14 weeks of pregnancy. It is to date your pregnancy and give you a due date. Sometimes, depending on how certain you are about your last period date, this may be used to work out the due date over the scan date.
This is also the time you will be offered combined screening. This test looks for chromosomal abnormalities such as Down’s syndrome, Edwards Syndrome and Patau’s Syndrome. You can choose to be tested for all of these syndromes or for some of them. You can choose to opt out of screening all together. If you are more than 14 weeks, you will be offered test that can performed up to 20 weeks but is less accurate that the combined screening test.
The test combines the thickness of the back of your baby’s neck and a blood test. This will give you a ratio as to how likely your baby maybe affected. It is really important to know that this is a screening test; it’s not diagnostic. If you receive a low risk result, it means it’s there is a low chance that your baby is affected.
I think it’s really important to talk to your partner and make an informed choice about the combined screening test. Some of the reasons you may want to be tested include –
- To reassure you that everything is probably ok
- If you would consider terminating the pregnancy if there was something wrong with the baby
- To prepare for the birth if you know that something is wrong. Any abnormalities detected would require follow up so a plan can be made for the care of the baby at birth
Reasons not to have the test could be –
- If you don’t want to know if there is anything wrong with the baby
- If you would not terminate the pregnancy if you had a diagnostic confirmed result
- If knowing there was something wrong with the baby would be too stressful for the rest of your pregnancy
This decision is completely personal to you both and only you can make it.
If the result showed a high risk of your baby being affected, you will receive full counselling and be offered diagnostic testing. This test would give an accurate result. You don’t have to go ahead with this if you don’t want to. You will be given lots of help, advice and support to help you make a decision that right for you. There is also charity called Antenatal Results and Choices (ARC) that can provide you with help and support.
This scan is performed between 18 and 21 weeks. At this scan, the sonographer will be looking at the structures of your baby and ensuring everything is normal. It not possible for this scan to detect every problem. You may also be able to find out the sex of your baby. If you want a surprise, make sure you tell the sonographer so they don’t tell you in error! If your pregnancy is low risk and remains so, this maybe the last scan of your pregnancy.
The next blog will be on the schedule of antenatal care.
Please click here for more information on screening tests in pregnancy.