1st Trimester Screening

The tests performed in the first trimester of pregnancy include a dating scan, first trimester blood tests, a urine culture and a combined first trimester screen. A new test is also now available which can be done in the first trimester. This is called the non-invasive prenatal test (NIPT) and is discussed in a separate fact sheet.

Generally a woman will present to her GP for the diagnosis of pregnancy after a missed period. It is recommended that the first trimester blood tests are done at this point, but they can be done at any time during the pregnancy. The initial tests include a βHCG to diagnose the pregnancy, and then routine tests such as a blood group and antibodies, a full blood count, rubella serology, syphilis serology, HIV, Hepatitis B, Hepatitis C and a urine test for infection.

1st Trimester Screening

There are some other tests that I like to do as routine. These include iron levels and Vitamin D levels, thyroid function tests and a check for immunity to CMV, Varicella Zoster, Toxoplasmosis and Parvovirus. These tests are usually available for review at your first visit to your Obstetrician. Any tests that have not been ordered are usually ordered at that visit.

A dating scan is not a routine test, but it is a fairly standard test that is done early in pregnancy for most pregnancies. It can confirm the due date, especially in cases where the periods are not as reliable as hoped. As a general rule, at the time of the missed period (4 weeks), an ultrasound scan would find a gestational sac within the uterus. A small fetal pole is often visible by about five weeks and a heartbeat can be seen as early as five and half weeks. Ideally a dating scan should be done no earlier than six weeks after the last normal period, but it is most accurate for dating between 8 and 12 weeks gestation.

Another common test done in the first trimester, but is not part of routine screening is the combined first trimester screen, otherwise known as the nuchal translucency scan. This is generally done between 11-14 weeks gestation, but is ideally done at 13 completed weeks. This test is done in conjunction with some blood tests which are ordered for approximately 4-5 days prior to the scan. You will present for review at the end of the first trimester and the results of your tests will be discussed. Further testing may be required if any of the tests are abnormal.