ANTENATAL INVESTIGATIONS – BLOOD TESTS
Blood Group and Antibody Screen
Your blood group is important to determine during pregnancy for two reasons. Firstly, blood transfusions are required in approximately one in every 300 deliveries. Secondly, if you are a Rhesus (D) negative blood type (approximately 15% of the population) and your partner is Rhesus (D) positive, special measures are necessary as your baby has a 50% chance of also having Rhesus (D) positive blood. In some pregnancies, tiny amounts of blood leave the baby’s circulation and enters the mother’s circulation (this is more likely during a miscarriage, invasive procedures like chorionic villus sampling or amniocentesis, episodes of antepartum haemorrhage and during delivery). Your immune system recognises these fetal blood cells as foreign and attempts to destroy them by production of an antibody known as anti‐D. Before the 1960s this immune sensitization often resulted in the loss of subsequent pregnancies. Now anti‐D is extracted from donated blood and administered to the Rhesus (D) negative mothers, to prevent sensitization from happening in the above circumstances. There are also prophylactic doses given at 28 and 34 weeks gestation. At the time of delivery, a blood sample is taken from the umbilical cord to determine the baby’s blood group and if this is Rhesus (D) positive then a further dose of anti‐D is administered to the mother within 72 hours of birth. This is not necessary if the baby is also Rhesus (D) negative. For Rhesus negative expectant mothers The Australian Red Cross Blood Service has more information.
Full Blood Count
This test measures the levels of haemoglobin, an iron‐containing protein used to transport oxygen in your blood. If you have suffered particularly heavy periods or have had a number of pregnancies in fairly quick succession, haemoglobin levels may be low (anaemia). Vegetarians may also have low haemoglobin due to vitamin B12 deficiency. Some families with backgrounds from the Mediterranean or South‐East Asia can have an inheritable form of mild anaemia called thalassemia. Confirmation of such a diagnosis is done by a haemoglobin electrophoretogram. If your partner has the same form of anaemia, your baby is at risk of a more major and serious degree of thalassemia.
Most people born in the last 25 years will have been immunised against Rubella (German measles) during childhood. Your immune status should be checked prior to conception or early in pregnancy. If you are not immune, you could contract the disease. Rubella can cause your unborn child to develop heart abnormalities, blindness and deafness. If you are not immune, it is important to avoid contact with potential carriers and to have re-immunisation after delivery.
This is moderately uncommon infection in most communities and many people have been vaccinated before travelling overseas. However, certain populations have higher levels of Hepatitis B. Chronic Hepatitis B acquired during childhood can be associated with the development of cirrhosis, chronic hepatitis and even cancer of the liver. Hepatitis B virus can be transmitted to the baby during delivery. To reduce this possibility, babies of mothers with Hepatitis B are given a concentrated dose of antibody at the time of delivery (Hepatitis B hyperimmune‐globulin) and immediate vaccination.
While uncommon, Hepatitis C can be acquired from administering drugs intravenously with unsterile needles, from unsterile tattooing and rarely from blood transfusions. Most women with Hepatitis C can safely deliver vaginally and breastfeed except in the circumstances of active viral replication (measured by Hepatitis C RNA). Postnatally, maternal Hepatitis C can now be effectively cured by specific anti-viral medications.
HIV‐positive women can lower the risk of transmission to their babies by the use of anti‐retroviral drugs, avoiding breast‐feeding and possibly by the choice of a Caesarean section for delivery.
Syphilis is a very uncommon disease in Australia. If it is not detected and left untreated it can have significant impact on the developing fetus. If discovered before 16 weeks gestation it can be readily treated with antibiotics such as penicillin and with a significantly better outcome for the baby.
This fetal protein is detectable in minute amounts in maternal blood, however if there is a defect in the baby’s spine (spina bifida) higher levels are detected. If so, further investigations will be necessary. This blood test is done at approximately 15‐18 weeks
2 Hour 75g Oral Glucose Tolerance Test
This test is necessary to determine whether you have gestational diabetes. In pregnancy your insulin requirements double by 28 weeks gestation (due to placental hormones). Most pregnant women produce sufficient insulin, but 2% can’t and will develop a temporary form of diabetes, known as gestational diabetes. Having high levels of glucose in your blood can result in excessive growth of your baby, making delivery difficult (even by Caesarean section). Your baby may also be at risk of low glucose levels (hypoglycaemia) after delivery. The test is normally done at 28 weeks. Some women will require a test earlier due to pre-existing glucose intolerance, being over 40 years of age, polycystic ovarian syndrome, a strong family history of diabetes or a past history of very large babies.
ANTENATAL INVESTIGATIONS - MICROBIOLOGY
Most women who have bacteria in their bladders will experience the symptoms of a urinary tract infection, such as burning and urinary frequency. Approximately 5% of women who have bacteria in their bladder have no symptoms. This is referred to as asymptomatic bacteria. If untreated, this bacteria can ascend into a pregnant woman’s kidneys, causing preterm labour and delivery. This midstream urine examination is usually done at the booking visit and will not need to be repeated unless you have symptoms of urinary tract infection.
Swab for Group B Beta Haemolytic Streptococcus
Group B Haemolytic Streptococcus (GBS) is a kind of bacteria found in the gut (rectum and anus), perineum or vagina of approximately 20‐30% of normal, healthy women. It is usually harmless during pregnancy, but is important after your waters have broken (whether you are in labour or not), as it may travel up through the vagina and cervix, to cause infection in your unborn baby. You will usually be tested for this bacteria at 35 weeks gestation. If the swab is positive then you need antibiotics during labour to prevent the baby from getting early streptococcal infection, such as pneumonia. Even if you have taken antibiotics during labour, there is a chance that your baby may develop an infection within the first 8 weeks of life, possibly leading to streptococcal meningitis. The baby’s health in the first month of life should therefore be monitored, watching for fever, feeding difficulties, lethargy and irritability. Any concerns should then be promptly raised with your General Practitioner or Paediatrician.
ANTENATAL INVESTIGATIONS - ULTRASOUND
Obstetric Ultrasound Facts
Typically an ultrasound is done at your initial booking visit to assess the size of your baby in order to confirm when your baby is due. This ultrasound also confirms the pregnancy is correctly located within the uterine cavity, that there is a heartbeat and detects whether there is just one baby or twins.
At later visits during your pregnancy, Dr Roper uses his ultrasound machine to confirm the position of the baby, the heart activity and amniotic fluid volume.
There are several times during your pregnancy when more specialised ultrasound is required such as screening for Down Syndrome at 12-13 weeks and detailed anatomy scan at 19 weeks gestation. For these you will be sent to either Sydney Ultrasound for Women at one of their many practices (the closest being at Kogarah), or to Shire Medical Imaging (Gibbs St, Miranda). Both services are managed by Obstetrician-Gynaecologists with subspecialisation in ultrasound.
Ken will perform a bedside ultrasound at your initial consultation. This is usually around 8 weeks (or sometimes sooner if there has been a past history of miscarriage). An ultrasound at the gestational age of 8 weeks can determine the presence of twins and is used to check for the fetal heartbeat.
Nuchal Translucency Scan
Ken refers his expectant parents to specialised ultrasound practices for this scan. Historically this scan was used to determine the level of risk for Down syndrome. This ultrasound may also detect gross anatomical abnormalities or markers of other kinds of chromosomal abnormalities.
Down syndrome was described in 1866 by a British physician, John Langdon Down, who called this condition ‘Mongolism’. In the 1960s it was discovered that people with Down syndrome had three, rather than two of chromosome number 21 (hence the other name: ‘trisomy 21’).
There is a relationship between advanced maternal age and the incidence of Down syndrome. The eggs that a women has in her ovaries have actually been present since prior to her own birth. They may have suffered genetic damage, possible leading to mutation, over time. The risk of mutation is therefore increased in older women. Sperm, in contrast, are produced only about 70 days prior to ejaculation, therefore the age of the father has little effect on the risk of Down syndrome. Despite the fact that older women are at greater risk, the majority of Down syndrome children are born to women who are under the age of 37, simply because there are many more of them pregnant than older women.
Several decades ago older mothers (typically 37 years and above), were all offered an invasive test such as an amniocentesis or a chorionic villus sampling to demonstrate that their baby did not have Down syndrome. During the early 1990’s it was found that ultrasound could show subtle signs that were suspicious of Down syndrome. These include a thicker layer of fluid under the skin at the back of the baby’s neck and the absence or reduced size of the nasal bone.
If a couple is discovered to have a baby with a high risk for Down syndrome there are several options for further testing. These include invasive diagnostic tests: chorionic villus sampling and amniocentesis. In these tests, a needle is used to obtain either a placental biopsy or amniotic fluid, respectively. These are reserved for those pregnancies at particularly high risk, typically >1:50. For those couples with a risk between 1:50-1:300 there is more recently available tool known as a non-invasive prenatal screening.
Non-invasive pre-natal screening (NIPS)
There are a variety of commercial tests available including ‘Harmony’, ‘Panorama’ and ‘GeneSyte’.; These have been commercially available in Australia since February 2015, prior to which specimens were sent to the United States for analysis. In 2006 it was discovered that scientists could detect tiny fragments of placental genetic material within the mother’s bloodstream, which very closely reflects the fetal genetic composition. The proportion of placental material in the blood is analysed and if there is a greater than expected amount of a particular chromosome then this indicates the need for an invasive test.
Some couples will choose to have non-invasive prenatal screening even in the context of an apparently normal nuchal translucency ultrasound, because the capacity to detect Down syndrome is far greater. The capacity to detect Down syndrome using age as a screening tool is 33%, the nuchal translucency scan is 90% and the non-invasive prenatal screening is 99.9%.
Non-invasive prenatal screening can’t detect all possible fetal chromosomal abnormalities (there are hundreds) but does detect the most common ones: Trisomy 21 (Down syndrome), Trisomy 18 (Edward's syndrome) and Trisomy 13 (Patau's syndrome) as well as abnormalities of the sex chromosomes, X & Y.
19 Week Morphology Scan
Most couples will elect to have this ultrasound. The ultrasound looks for any abnormalities in the baby that may require investigation and treatment after delivery. These range from mild conditions such as talipes (club foot), which usually responds to physiotherapy, through to more serious abnormalities requiring surgery, such as cleft lip, and those that are incompatible with ongoing life. The ultrasound also determines the location of the placenta, and its proximity to the cervical canal, which may affect decisions regarding labour and delivery. It is usually possible to determine the baby’s gender at this time. Some couples are eager to know, whilst others prefer to wait for a surprise at delivery.