Antenatal Tests and Important Decisions

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Antenatal Tests and Important Decisions


Antenatal Tests

It is recommended that you have the following tests during your pregnancy. These test results will help in assessing the well-being, of you and your baby. Your doctor or midwife can answer

Blood Tests in Early Pregnancy

Blood tests are ordered by your GP and are to be checked for the following:

  • Blood group, Rh factor, haemaglobin (iron) level, iron studies;
  • Your immunity to Rubella (German measles);
  • Vitamin D;
  • Sexually transmitted diseases such as Chlamydia,  Syphilis and HIV;
  • Hepatitis B;
  • Hepatitis C;
  • Urine test to check for infection; and
  • Fasting BSL or alternatively an early Glucose Tolerance Test (GTT) for some women with higher risk of diabetes in pregnancy.

Ultrasound Scan

This is a procedure which uses sound waves to form images of your baby. There  are two scans routinely taken during your pregnancy. The first scan is called the dating scan and it is usually organised by your GP for between 7 and 13 weeks plus 6 days. This scan is most often used to ascertain your baby’s due date.

The second routine  scan is called ‘level 2 morphology scan’ and this is done between 18 and 20 weeks of pregnancy. This is a very detailed scan that looks closely at your baby, the position of the placenta and whether  your baby is growing well. The scan takes about an hour.

Early screening for Trisomy 21 (Down Syndrome), Trisomy 18 and 13

This test is available to you between 11 and 13.6 weeks gestation. It is a combined  test that consists of a blood test done by 13.4 weeks gestation and a scan of your baby that shows your possible chance of having a baby with Down Syndrome, trisomy 13 or 18.

Genetic Material (DNA)

DNA is arranged in the human body in packets called chromosomes.  Every cell in the human body should contain 46 chromosomes, there are two copies of chromosomes numbered 1 to 22 (one from each parent) as well as two sex chromosomes  (XX girl or XY boy).

Trisomy means that there are 3 copies of a certain chromosome  in every cell, for example Trisomy 21 (Down Syndrome) means three copies of chromosome number 21 in each cell. This obviously affects the way a baby develops and causes conditions  that may affect the babies life. Chromosomal  abnormalities can occur in any pregnancy but are more common  in babies of older mothers.

The first trimester screening result measures the nuchal translucency (thickness at the back of the fetal neck as seen on ultrasound) and the blood test measures the level of two hormones produced  by the placenta (PAPP-A and BHCG). It is very important  that you have both tests with the blood test first to obtain an accurate result.

This test is specifically designed to screen for Trisomy 21, Trisomy 13, and Trisomy 18. Other  genetic abnormalities however, may be revealed after further investigating the test results.  Remember some abnormalities are mild but some can be severe in nature.

If you are unsure whether you wish to have this screening test please discuss this with your GP or at your first appointment at the WHC if prior to 13 weeks plus 6 days.

Understanding test results and options

If you do not understand your test results fully please discuss this at your  next antenatal appointment.

As a guide when interpreting results, the higher the number the lower the likelihood that your baby will have Trisomy 21, 18 or 13.

1:250 or above means less chance, for example your result may say 1:1000.

1:250 or numbers lower than this are classed as a higher likelihood of baby having a chromosomal abnormality, for example 1:50.

Options then include:

  • Chorionic  Villus Sampling (CVS) or Amniocentesis for a more definitive diagnosis;
  • non-invasive prenatal testing (NIPT);
  • detailed ultrasound at 16-20 weeks;
  • no action - parents may choose to accept the results with no further investigation.

If you require information about your options  and the tests stated please ask to speak with one of our doctors who will be able to comprehensively explain what each test/result means. We also have a handout that is used in conjunction with a consultation  explaining this information further. No tests will be done without informed consent and counselling from one of our obstetric doctors.

Please remember the majority of pregnancies with abnormal results will have a normal outcome.  It is also important  to note that not all abnormalities that might affect a baby can be identified before birth.

Second Trimester screening for Down Syndrome and Spina Bifida

This is a blood  test, that looks at your likelihood of having a baby with Down Syndrome. It can be done between 14 and 20 weeks plus 6 days if you were not able to do the first trimester screening. It also identifies  if there is an increased chance of neural tube defect that is present in Spina Bifida.

Women who have a negative blood group

All women who are Rh Negative receive injections called “anti-D” at 28 weeks and 34 weeks. This prevents your body from making antibodies to your baby’s red cells. If you have a negative blood group (Rh Negative) it is important that you understand what this means for you and your  baby. Please discuss it with your midwife or doctor.

It is very important  you have your recommended 26 week blood tests including your blood group and red cell antibodies checked before your 28 week antenatal check. Anti D cannot be given until results from this test are available.

Diabetes in Pregnancy

It is recommended that all women  have a test for diabetes in pregnancy (POGTT)  attended at 26 weeks, this includes women  who may have had this test early in pregnancy.

Undiagnosed or uncontrolled diabetes may lead to:

  • Bigger or smaller babies due to the placenta not functioning properly
  • High blood sugar levels at birth for baby and sometimes breathing difficulties
  • Higher risk of baby developing obesity or diabetes  as an adult
  • Mother  has higher risk of developing pre-eclampsia or hypertension

A booking is required at a pathology service to have your POGTT attended. Please note this is a fasting test for pregnant women  which means no food including chewing gum and cigarettes for at least 8 hours prior and plain water only during the fasting period.

Blood tests at 26-28 weeks

At 26-28 weeks bloods are taken for diabetes (POGTT),  haemaglobin and red cell antibiodies.

The results of these tests will be discussed with you at your 28 week visit and any recommendations/follow up made. It is therefore very important that you ensure these tests have been completed prior to your 28 week antenatal appointment.

Group B Streptococcus

At 36 weeks you may be weighed and asked to provide a specimen of urine. The midwife will also ask you to collect a vaginal swab. The swab is used to detect a bacteria called Group B Streptococcus (GBS). 15%-25% of the normal population carries this bacteria which is not harmful to you. However in 1%-2% of cases it can be passed onto  the baby during the birth process, which can cause the baby to become ill with symptoms of sepsis.

THS policy recommends that you be treated with antibiotics (given into your vein) during labour  if GBS is detected. This will help protect your baby from infection and reduce their risk to around 0.1%.

All babies whose mothers are GBS positive are closely observed  for signs of illness, particularly in the first 24 hours after birth. In some cases where  antibiotics were  not given in labour those babies will need to be observed for 48 hours.

Some consideration needs to be made antenatally about care options for your baby when it is born.  This involves some injections  and tests as well as safe sleeping and safe care.

It is important you read information about Sudden Infant Death Syndrome (SIDS) and bed sharing. Because of the risk involved the THS recommends that you do not bed share with your baby.

Information on caring for your newborn and SIDS is further discussed in Your baby is born section of this manual.

Important decisions for the care of your baby after birth

Some consideration needs to be made antenatally about care options for your baby when it is born.  This involves some injections  and tests as well as safe sleeping and safe care.

It is important you read information about Sudden Infant Death Syndrome (SIDS) and bed sharing. Because of the risk involved the THS recommends that you do not bedshare with your baby.

Information on caring for your newborn and SIDS is further discussed more  later in this booklet.

Hepatitis B Vaccination for the newborn

Hepatitis  B is a virus that can cause acute or chronic liver disease. If a baby contracts this disease, symptoms fortunately may be mild for your baby. However,  most babies will go on to be chronic carriers which can cause liver cancer later in life and also pass the virus onto others or their own children.

Hepatitis B is spread easily through  body fuid secretion including blood (cuts or sores, body piercing, sharing toothbrushes, razors),  saliva (kissing, baby dribbling), semen, vaginal secretions and breast milk.

Immunisation is considered the most effective way of preventing hepatitis B and if given at birth is more  likely to provide life long immunity.

The THS offers vaccination to your baby prior to leaving the hospital. Your baby will need a further three more doses of the hepatitis B vaccine to be fully immunised. These three doses are given at six weeks, four and six months of age in a combination with other routine infant immunisations.

The vaccine is considered  safe to give to your baby after birth. It is well tolerated and minor  side effects may include local swelling and redness at injection site, mild fever and occasionally irritability or refusal of feeds for a short time. These symptoms are short lived.

Premature  babies less than 32 weeks gestation may have a lower  immune response to hepatitis B vaccine and may need a hepatitis B booster at 12 months of age. The vaccination should only be delayed if your baby is very unwell or has a high fever. Antibiotic  treatment  is not a reason to delay hepatitis B vaccination.

For further information visit Immunise  Australia

Vitamin K

Vitamin K helps blood to clot. It is produced  by the body and is essential to prevent rare but serious bleeding in the newborn.  Some babies do not produce enough Vitamin K until they are a few months old. They do not get enough Vitamin K from their mothers during pregnancy and there is not suffcient Vitamin K for their needs in breastmilk or formula.

The Royal College of Paediatricians recommend  that all babies be given the Vitamin K injection to prevent  a now rare bleeding disorder called Vitamin K Defciency Bleeding (VKDB). Prior to the implementation of routine injection of Vitamin K, some untreated babies who suffered from VKDB sustained brain damage or even died.

The injection is the most reliable way to provide enough Vitamin K to protect your baby for months until he/she can produce it themselves.

Alternatively Vitamin K can be given to babies orally. Because Vitamin K is not absorbed  as well  when  given by mouth, your baby must have three doses over the course of four weeks. If your baby vomits within an hour of swallowing the Vitamin K, the baby will need to repeat the dose. Limitations around giving vitamin K orally include premature or sick babies; mother’s who have a history of blood clots, epilepsy or tuberculosis.

Within  Australia, Vitamin K has been administered to babies for over 50 years with no documented problems. Earlier studies suggested that injections of Vitamin K may be linked with childhood cancer. The National Health and Medical Research Council conclude from more recent studies that Vitamin K is not associated with childhood  cancer, whether it is given by injection or by mouth.

In order to prevent the rare but potentially fatal disease (Vitamin K Defciency Bleeding), medical authorities strongly recommend   that all babies be given Vitamin K. This includes babies who are premature or sick, and babies having any surgery (including circumcision).

We require your verbal consent to allow administration of Vitamin K. If you decline Vitamin K for your baby a paediatrician will see you in the postnatal period to ensure you are making an informed choice for your baby.