Through your pregnancy there will be a number of tests offered to you. Some of these are optional while others (the majority) are strongly recommended. These include...
An ultrasound in the first trimester is a good idea to clarify your estimated date of delivery (EDD). Often this will be done at the First Trimester Screen (below) or at your initial visit to Dr Murphy.
First Trimester Screen (FTS)
This is a screening test for Trisomy 21 (Down's Syndrome), Trisomy 13 and Trisomy 18. These are all chromosomal disorders in which your fetus has an extra copy of either chromosome 21, 13 or 18. Downs Syndrome is compatible with extra-uterine life, usually associated with intellectual and physical disability. Trisomy 13 and 18 are not compatible with extra-uterine life for more than a few days.
The FTS involves a calculation using your age, 2 hormone levels, (Papp-A and free bhCG), and the Nuchal Fold thickness from the back of the fetal neck. The result is presented as a risk, eg 1:50, 1:200, 1:10,000.
Any result with >1:300 probability of on of the above disorders will be classified as "high risk" and you will be offered a diagnostic test. These are outlined below and will provide a "yes/no" answer. 5% of all women having the FTS will screen as "high risk", ie 1:20 and 90% of cases of Down's Syndrome will be identified.
Chorionic villus sampling (CVS)
Performed at 13-14 weeks gestation, a needle is usually passed through the abdominal wall into the placental bed and cells are obtained for analysis. A preliminary result will be available in 48 hours, with a final result in 2 weeks. A CVS is associated with a 1:100 risk of pregnancy loss. You will require an Anti-D injection if you are a negative blood group.
This the other possible test after a high risk FTS. It is performed at 15-16 weeks and obtains cells from the amniotic fluid around your fetus. It is associated with a 1:300 risk of pregnancy loss. Anti-D is required in you are a negative blood group.
Maternal Serum screening (MSS) or the "triple test"
This is an older test largely superseded by the FTS. It is performed at 16 weeks and provides a result similar to the FTS, however only 60% of cases of Down's syndrome are detected and 5% of pregnancies will still screen "high risk" and required an amniocentesis to provide a diagnosis.
19 week Anatomy ultrasound.
This is an essential test in any pregnancy. Your fetus will be screened for a range of anatomical problems. The placental site will also be determined and if this is close to the cervix may need to be rechecked later in the pregnancy, usually at 32-34 weeks.
At 26-28 weeks you will be tested for diabetes, either with a 50g Glucose Challenge (G50) if you are low risk for gestational diabetes (GDM), or a full Glucose Tolerance Test (GTT) if you are high risk. The G50 is non-fasting and involves a sugar drink followed 1 hour later by a blood test. For a GTT you are required to be fasted for at least 10 hours, and blood tests are done at 0, 60 and 120min after a 75g glucose load. In addition a test for iron stores (ferritin), a full blood count and red blood cell antibody screen will also be performed at the same time.
Rhesus negative women will have prophylactic anti-D at 28 and 34 weeks to reduce the incidence of Rhesus iso-immunisation in subsequent pregnancies. Anti-D is also given after any bleeding in your pregnancy, after any invasive tests such as a CVS or Amniocentesis and after the birth of your baby if they are Rhesus positive.
Group B Streptococcus
All women planning a vaginal delivery are screened for group B Streptococcus (GBS) at 36 weeks. GBS is a bacteria found in the vaginas and digestive tracts of 20-25% of women and rarely causes problems for mothers. It is a common cause of severe life threatening sepsis for newborns. Given its susceptibility to common antibiotics, treatment is recommended for GBS positive women in labour. Women who have had a GBS urinary tract infection in the current pregnancy and those women who have had a previous GBS affected baby do not require screening as they will all be treated.
Dr Murphy will be able to explain these tests and answer any questions you may have.