Screening during Pregnancy
There are an increasing number of screening and monitoring procedures now being undertaken during pregnancy. Some of these procedures have been part of maternity care for decades despite a lack of evidence that they offer any benefits to either the mother or the baby.
It is important that you ask your midwife or doctor to explain the screening tests and procedures being offered to you. You need to know what they involve, and the risks and benefits of having them.
You can choose whether or not to have any of these tests.
Blood tests (maternal serum screening)
Weight checks and BMI assessments
Ultrasound Scans
Amniocentesis
Polycose and Oral Glucose Tolerance Tests (GTT)
Screening for Domestic Violence & Sexual Abuse
At one of your first antenatal visits your midwife or doctor will usually give you a form to go to a medical laboratory for your first blood tests. Six different tests are carried out on the first blood sample you agree to give. The tests are:
- Your blood group and Rhesus factor
- Full blood count
- Hepatitis B
- Rubella
- Syphilis
- HIV
The decision on whether you choose to have any of these tests done on your blood sample is yours to make.
Blood group and Rhesus factor
Your blood is tested to find out or confirm your blood group – A, B, O or AB.
It is also tested to see if you are Rhesus Factor (Rh) Positive or Negative. Rhesus factor is a substance most people have in their blood. Around 85% of the population has the rhesus factor and the remaining 15% do not. If you do not, you are Rhesus Negative.
If you are Rhesus Negative and your first baby is Rhesus Positive it will not be a problem for your first baby, but it may result in severe anaemia for other Rhesus positive babies in subsequent pregnancies. This happens if some of the first baby’s Rhesus positive blood gets into your blood stream during pregnancy or labour and your blood creates antibodies. Treatment is needed to prevent the antibodies in your blood from crossing the placenta and attacking and destroying the next Rhesus positive baby’s red blood cells, leading to haemolytic anaemia. The treatment is an injection of Anti-D given after the birth of your first baby, or after a miscarriage or a termination of pregnancy (abortion).
If you experience any bleeding from the vagina during pregnancy it is important to tell your Lead Maternity Carer (LMC) as soon as possible.
If you are Rhesus Negative you will be offered a second blood test at around 28 weeks of pregnancy in order to check on whether or not your blood contains antibodies.
Full Blood Count
Your blood is tested to see if there is a healthy amount of iron in your circulating blood and also in your body’s iron stores. Low levels of iron/ haemoglobin (Hb), the oxygen-carrying component of red blood cells, may mean that you are anaemic. Very low iron levels can make you feel tired and lacking in energy. There is also evidence that it can lead to premature labour.
However, it is natural for iron levels to drop during pregnancy due to the large increase in fluid or plasma which dilutes the red blood cells.
Eating foods that have plenty of iron in them, such as leafy dark green vegetables, wholemeal breads, potatoes, raisins and prunes, and lean red meat is recommended. Vitamin C helps your body absorb the iron in your diet, so it is good to eat fruit with your iron rich foods.
Hepatitis B
Your blood will be tested to see if the Hepatitis B virus is present. Hepatitis B is a virus that can cause inflammation of the liver. Most infected people are carriers of Hepatitis B and do not have any symptoms of illness. Mothers who have the virus or are carriers are likely to pass the infection on to their newborn baby. Babies who become infected risk dying of liver-related diseases.
If you have Hepatitis B your baby will be offered a course of vaccinations that start within two hours of birth. Most babies who are vaccinated will not become infected with the Hepatitis B virus.
Rubella (German measles)
This test is done to see if you have antibodies to rubella. If you catch rubella during the first 16 weeks of pregnancy it can cause miscarriage, stillbirth or severe problems such as deafness, brain damage, and heart defects in your baby. If you have no rubella antibodies in your blood you will need to stay away from anyone who has rubella while you are pregnant and you will be offered a rubella vaccination after you have given birth.
Syphilis
Your blood will be tested to check for the presence of syphilis. Syphilis is a rare sexually transmitted disease, but it has become more common in recent years. If your blood test reveals that you have syphilis you will be offered antibiotics in order to prevent serious health problems for you and your baby as the infection can be transmitted from mother to baby during the birth.
HIV/AIDS
New Zealand has recently begun routinely offering pregnant women an HIV test as part of the first antenatal blood tests despite the fact that few women are diagnosed with HIV during pregnancy. Most HIV positive women in New Zealand know they have the virus prior to becoming pregnant.
The Human Immunodeficiency Virus (HIV) can cause AIDS, and if you have HIV there is a 25% chance of passing the virus to the baby during pregnancy or during birth. Women with HIV are offered a combination of treatments that reduce the risk of the baby becoming infected to less than 1%.
Weight checks and BMI assessments
Gaining weight is an essential part of growing a healthy baby no matter what your weight was prior to becoming pregnant. The recommended average weight gain for a healthy mother carrying one baby is between 11 – 16 kg. If you were underweight when you became pregnant you may need to gain more weight; if you were overweight a smaller weight gain will be recommended.
Despite the widespread practice of measuring maternal weight gain during pregnancy, almost no studies on assessing the usefulness or negative consequences of weighing women have been published. Weighing women at each antenatal check-up is now recognised as a poor method of assessing how well your baby is growing. However,the results of some screening tests such as the blood tests (maternal serum screening) taken when screening for Down syndrome require maternal weight in order to produce an accurate assessment of risk.
BMI (body mass index) is a measurement of body fat based on height and weight. However, for many women, particularly those of Maori and Pacific descent, the BMI which is based on “healthy” weights for athletic people of Caucasian/European ethnicity does not provide an accurate or useful assessment. Weighing women at each antenatal check-up is now recognised as a poor indicator of assessing how well your baby is growing. Weight gain in pregnancy related to a woman's BMI before she becomes pregnant is now considered to be a better assessment. Your BMI should be calculated at your first antenatal check up.
Ultrasound ScansAn ultrasound scan is a way of seeing the growing baby and hearing its heartbeat during pregnancy. Having an ultrasound scan has now become a routine part of pregnancy care despite a lack of evidence that it results in improvements in outcomes for the baby.
Ultrasound scans carried out during the first three months of pregnancy are used to check the age and size of the baby, count the number of babies, and predict the due date of the baby. Scans done during this time are only able to detect some major abnormalities, and detection rates depend on the skill and expertise of the person doing the scan as well as the quality of the scanning equipment.
Ultrasound scans are also commonly performed between 18-20 weeks of pregnancy and involve examining the baby for any sign of abnormalities, as well as checking on the number of babies and the position of the placenta. However, it should be noted that only half of all major abnormalities are able to be detected by an ultrasound scan. Even if no abnormalities are seen, there is still a possibility that the baby will have a problem.
Nuchal Translucency (NT) Scans
An NT scan is performed when a mother is between 11 weeks and 13 weeks and 6 days pregnant, to assess the risk of the baby having Down syndrome or a few other chromosomal abnormalities. During the scan the thickness of the fold of skin at the back of the baby’s neck is measured. An NT scan does not provide an accurate diagnosis of Down syndrome; only an amniocentesis can do that.
There are now two options for screening for Down syndrome. First trimester screening combines the NT scan result with a blood test, and other information such as your age and weight to calculate the chance of your baby having Down syndrome. Second trimester screening does not involve a NT scan and combines the result of a blood test with other information such as your age, weight and how far through your pregnancy you are. Having a NT scan without a blood test is no longer recommended due to the high rate of false positive results. Further information on Screening for Down syndrome can be found in the Screening Programmes section on the National Screening Unit website: www.nsu.govt.nz.
For more detailed information on ultrasound scans please contact Women’s Health Action Trust on (09) 520 5295 or email: info@womens-health.org.nz and request a copy of “Ultrasound Scans during Pregnancy” leaflet.
AmniocentesisThis is a diagnostic procedure that involves inserting a needle through the abdominal wall of the mother and withdrawing a small quantity of the amniotic fluid that surrounds the baby. It is usually carried out between 15 and 18 weeks of pregnancy. There is a risk of 0.5-2% of miscarriage following the procedure and many women experience cramping and/or mild bleeding in the days afterwards. It takes two to three weeks to get the results and if an abnormality is found, the woman/parents must then decide whether or not to terminate the pregnancy.
Polycose and Oral Glucose Tolerance Tests (GTT)Screening for gestational diabetes has also become a routine part of antenatal care for the majority of pregnant women. Most women are referred for a screening test at 28 weeks of pregnancy. Women go to their local diagnostic laboratory where they are given a “polycose” drink (50g of glucose). One hour later a blood sample is taken. If this blood sample contains more than 7.7mol/ml of glucose an Oral Glucose Tolerance Test – a diagnostic test – is recommended.
For a Glucose Tolerance Test you will be required to fast for 12 hours (overnight) and then a blood sample will be taken to measure your fasting blood glucose level. You will then be given 75g of glucose to drink and another blood sample will be taken two hours later to check your blood glucose level. These tests carry their own physical “challenges” or stressors to both you and your unborn baby.
Screening for Domestic Violence & Sexual AbuseThere are various other kinds of “screening” now being undertaken during pregnancy. These include being asked about domestic violence, and sexual abuse. While this sort of questioning does not involve the type of physical invasion that blood tests, ultrasound scans and OGTT tests do, they are all part of an increasing number of risk assessments and diagnostic tests currently being routinely carried out on pregnant women.
References available on request