An Ultrasound Scan in early pregnancy can determine the gestation of pregnancy if the menstrual dates are uncertain. A scan is needed if there is pelvic pain or vaginal bleeding in early pregnancy, to confirm there is a viable pregnancy inside the uterus.
Nuchal Translucency Scan (First Trimester Combined Screen)
A Nuchal Translucency Scan is done around 12 to-13.5 weeks as part of the First Trimester Combined screen. Imaging provides an overview of fetal structure and excludes major anomalies such as spina bifida and anencephaly. Measurement of the nuchal translucency on the back of the neck is combined with a blood test for placental function to provide a calculated risk assessment of chromosomal abnormalities involving chromosomes 21, 18, 13, X and Y. This test was mainly designed to assess the risk of a fetus have Trisomy 21 (three copies of 21 instead of 2) or Down Syndrome.
A Morphology scan is done around 20 weeks. This scan looks in more detail at the fetal anatomy to exclude structural concerns that may need further scanning or follow-up. The genital area is imaged at this scan so it is possible to find out the gender.
This scan also checks how close the placenta is to the cervix. If the placenta is over the cervix or very close to the cervix, then it would not be safe to have a vaginal delivery due to the risk of life-threatening bleeding. At the 20-week scan if the placenta is less than 2 cm from the cervical opening, then this is considered a low-lying placenta. A follow-up scan in third trimester around 34 weeks is recommended to check the placental site.
During pregnancy, the part of the uterus that is just above the cervix expands to become the lower segment of the uterus. If the placenta has implanted close to the cervix and is low lying at 20 weeks and the part of the uterus between the placental site and the cervix expands, then by third trimester the placenta will be further away from the cervix and not a problem. Over 95% of placentas that are low lying at 20 weeks will be well out of the way by third trimester.
Third trimester scans
In third trimester there may be a scan for placental site if the placenta was low lying at 20 weeks. Scan(s) for fetal growth and wellbeing are arranged if there is vaginal bleeding, if there is maternal hypertension or gestational diabetes, if there is decreased fetal movements felt, or if baby feels too large or too small for gestational age.
Antenatal Screening Tests
When a General Practitioner refers a patient for antenatal care, they will also refer for Antenatal Screening tests. These may include:
Full blood count to check Haemoglobin for anaemia.
Blood Group and Antibody screen. The most common red cell Antibody ls Anti D which can occur in Rhesus negative women. If a Rhesus negative woman is pregnant with a Rhesus positive baby and some of baby’s Rhesus positive cells leak into the maternal circulation via the placenta then antibodies against the D protein on the red cells can form. Once a woman has become sensitised and formed Anti D antibodies then these antibodies can cause problems in a future pregnancy. They can cross the placenta and attack baby’s Rhesus positive cells causing anaemia in the baby or neonatal jaundice from excess breakdown of red cells. If a Rhesus negative woman has not developed Anti D antibodies, then preventative doses of Anti D are given around 28 weeks and 34 weeks gestation. This Anti D antibody will be attracted to any Rhesus positive red cells in the maternal circulation and destroy them before sensitisation can occur. There are several other red cell antibodies that can be detected. It is important to test for red cell antibodies during pregnancy. If antibodies are present, baby will need to be watched for jaundice after birth.
Serology will check for immunity to Rubella and for any exposure to syphilis, Hepatitis B, Hepatitis C, HIV and sometimes chicken pox.
Other screening tests may include renal and liver function including a random blood glucose; serum ferritin to detect iron stores, a screen for thyroid function, and screen for Vitamin D levels.
Screening tests are available to detect carriers of rare genetic disorders. These disorders may include cystic fibrosis, spinal muscular atrophy, or fragile X syndrome.
Combined first trimester screening for chromosomal abnormalities
The Nuchal Translucency screen can be combined with a blood test for proteins that come from the placenta and are markers of placental function. These are free Beta HCG and PAPP-A. When these levels are added into a formula with the nuchal translucency measurement, the calculation of the risk of Trisomy 21 (Down Syndrome) is more accurate than when based on the measurement alone. A low PAPP-A can be associated with a decline in placental function in third trimester so additional surveillance of fetal growth and wellbeing may be required. The blood test for free Beta HCG and PAPP-A needs to be collected after 11 weeks and at least three working days before the Nuchal Translucency scan. The easiest way to remember this is to book in for the scan and have the blood tests a week before.
Non-Invasive Prenatal Test
A Non-Invasive Prenatal Test can be collected after 11 weeks gestation. This blood test uses fragments of fetal DNA in maternal blood to estimate the number of copies of chromosomes 21, 18, 13, X and Y. (e.g. Down Syndrome is caused by 3 copies of chromosome 21 rather than normal 2 copies). This test can be taken if there is a higher risk of abnormal chromosomes, for example maternal age > 35, previous history or family history. This test is offered if the First Trimester Combined Screening calculates a high risk for a chromosomal abnormality. The NIPT will also indicate gender eg XX female or XY male.
If the screening tests are suspicious for a chromosomal abnormality, then the only way to find out if the chromosomes are normal, or not, prior to delivery is to have invasive testing performed. There is a small risk of miscarriage of 1 per 200 with these invasive tests.
Invasive testing involves a procedure under sterile conditions where local anaesthetic is injected into the skin of the maternal abdomen. Under ultrasound guidance a needle is used to collect fetal cells for investigation of chromosomes.
Chorionic Villus Sampling can be performed as early as 13 weeks. Under ultrasound guidance a needle is inserted into the placenta and fetal cells are extracted. After 16 weeks Amniocentesis can be performed where under ultrasound guidance a syringe aspirates fluid containing fetal cells from around the fetus.
Fetal cells can be treated with fluorescent stains to diagnose the number of chromosomes 21, 18, 13, X and Y in each cell. This result can be available within 48 hours. Harvested fetal cells can be grown in culture which may take two weeks. These cultured cells can be used for a microarray that can look at all the chromosomes in detail. Numbers of chromosomes and any abnormal chromosomes can be diagnosed.
Glucose Tolerance Test (GTT)
A Glucose Tolerance Test is a screening test for Diabetes during pregnancy. It is usually done around 26 to 28 weeks gestation and after 26 completed weeks. At the same time blood is taken for a blood count (haemoglobin, platelets etc), serum ferritin (iron storage protein that indicates whether there is enough iron intake), and red cell antibody screen.
For the Glucose Tolerance Test an appointment needs to be made with a pathology service (Mater Lab, QML, SNP) for a date after 26 weeks gestation. Some request forms have phone numbers on them but an appropriate phone number for the preferred location may need to be found on the internet.
The night before the GTT, there is to be no eating after 10 pm. Water can be drunk for breakfast, but no solid food.
Next morning at pathology at the appointed time a fasting blood test will be collected. A sweet drink with a measured amount of glucose in it will be given. One hour after the drink, a blood test to see how much glucose has been absorbed will be collected. Another hour later, a third blood test will be collected to see how the body has coped with the sugar load. All three blood sugar tests have to be below certain levels to pass the test and avoid the diagnosis of Gestational Diabetes.
Pathology prefers that participants stay there throughout the course of the test so something to pass the time is needed.
It is appreciated that this is not a pleasant test during pregnancy because of the fasting and the 3 blood tests. Many will find the sweet drink is not to their taste and some will feel fatigue after the test. However, it is a very good way of diagnosing diabetes in pregnancy.
To have diabetes in pregnancy there has to be a combination of two things. One is a genetic tendency to insulin resistance, which may run in families as late onset diabetes or polycystic ovarian syndrome. Insulin resistance can also occur in the overweight or obese. The second thing is the genetics of the placenta and the placental enzymes that process sugars. Some placental enzymes antagonise the function of insulin and make it less effective. So, this combination of these two genetic things will put blood sugars into the diabetic range during pregnancy. There is no way to prepare for the test or make the test less likely to be positive.
Most women who are diagnosed with Gestational Diabetes will have normal blood sugar levels when they monitor with finger prick testing. Some may have to adjust their diet and a smaller number may need medication or insulin injections to keep blood sugars in the normal range. If the blood sugars are consistently higher than normal, baby can make more insulin which acts as a growth hormone and can make baby larger than average. Babies affected by Gestational Diabetes are often larger than 4 kg. After birth, the extra insulin produced by baby can make its blood sugars lower than average which can make baby very unwell. It is important to diagnose Gestational Diabetes during pregnancy so that management can reduce the risk of a large baby or baby with low blood sugars.
Results of the Glucose Tolerance Test will be sent to my rooms electronically. To check the results prior to the next antenatal visit, ring the rooms, on the second working day after the GTT.
Third Trimester Blood Tests
Follow-up blood tests may be required if previous blood tests have detected anaemia, low serum ferritin (iron levels) or red cell antibodies. If there is high blood pressure then blood tests are taken. Pre-eclampsia, or the high blood pressure disease of pregnancy, can make platelets lower, and derange liver function and renal function. These changes can indicate the severity of the pre-eclampsia. The amount of protein in the urine is also an indicator of the severity of pre-eclampsia. If there is any bleeding in third trimester a blood count and serum ferritin can be checked. If there are decreased fetal movements felt, in addition to a CTG to monitor the fetal heart, a Kleihauer blood test collected. This blood test for Fetal-maternal haemorrhage detects any fetal cells in the maternal circulation. If there is leakage of a large amount of fetal blood through the placenta to the maternal circulation, this can make baby anaemic and decrease fetal movements.
Blood Tests during Labour and Postpartum
A Full Blood Count and Blood Group and Hold may be collected in labour or prior to caesarean delivery. Comparing the Haemoglobin before and after delivery can confirm the estimated blood loss from the delivery. If there is excess bleeding the Group and Hold can be used to cross-match for a blood transfusion. If there is high blood pressure, blood tests for liver function and renal function can be collected, as well as testing for protein in the urine.
After baby is born a Full Blood Count for haemoglobin levels and a serum ferritin for iron levels can be collected. This will determine if a postpartum blood transfusion or iron infusion are needed.