Obstetric Ultrasound
Early pregnancy ultrasound
Ultrasound scans are performed in early pregnancy to establish the dating and viability of the pregnancy - how pregnant you are and whether the fetal heart beat can be detected.
These scans may be requested by your doctor if you are uncertain about the dates of your pregnancy, if you have had complications such as bleeding, if you have risk factors for early miscarriage, or if there are concerns about ectopic pregnancy.
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These scans often require a transvaginal approach to better assess the early pregnancy, and this will be discussed with you if required.
First trimester screening
First trimester screening, also known as combined screening, is routinely offered to all pregnant women. This test uses a combination of ultrasound imaging and blood tests to assess the chance of your baby having trisomy 21 (Down syndrome), trisomy 13 (Patau syndrome), or trisomy 18 (Edwards syndrome).
The ultrasound scan also assesses the early anatomy of the fetus to identify major structural abnormalities so it is recommended even if you do not wish to have screening for these chromosome conditions.
This scan is best performed between 12 and 13 weeks. It is generally performed through the abdomen and it is useful to have a partially full bladder at the time of your appointment.
If you are uncertain about which pregnancy screening tests are right for you, your doctor or our expert genetic counsellor can provide further advice.
Early fetal anatomy survey
The early fetal anatomy survey is an ultrasound imaging assessment of the fetus, aiming to identify the small proportion of fetuses who have major structural abnormalities. It is also useful to determine the type of twins in the case of multiple pregnancy.
This scan is recommended for all pregnant women, even those who have had non-invasive prenatal testing for Down syndrome or who choose not to have such screening.
This scan is best performed between 13 and 14 weeks. It is generally performed through the abdomen and it is useful to have a partially full bladder at the time of your appointment.
Second trimester fetal anatomy survey
The second trimester fetal anatomy survey (commonly called the "anatomy scan") is recommended for all women. This scan assesses the detailed anatomy of the fetus, the position of the placenta, and the length of the cervix.
This scan is best performed between 19 and 20 weeks. It is generally performed through the abdomen and it is useful to have a partially full bladder at the time of your appointment. The length of your cervix will be measured during this scan as a short cervix is associated with an increased chance of preterm (early) birth. In a proportion of women and in those with risk factors for preterm birth, a transvaginal scan is required to accurately measure the cervix and this will be discussed with you at the time of the scan if required.
Third trimester ultrasound
Your doctor or midwife may request ultrasound imaging in the later part of the pregnancy. Commonly this is to assess the growth of the fetus if there is a suspicion that the baby may be too small or too big, to assess the position of the placenta if it was low at earlier scans, or to follow up an any concerns with the fetal anatomy. Increasingly, third trimester ultrasound is used to assess for rare but significant fetal abnormalities which cannot be detected in the second trimester.
These scans are generally performed through the abdomen and it is useful to have a partially full bladder at the time of your appointment.
Chorionic villus sampling and amniocentesis
Chorionic villus sampling (CVS) and amniocentesis are procedures used to obtain a sample of DNA from the fetus. This may be performed if screening tests indicated an increased chance of a chromosomal condition (such as Down syndrome), if one or both of the parents carry a genetic condition which they could pass on to their children, or if there are abnormalities detected on ultrasound scans.
CVS involves taking a sample of cells from the placenta and is usually performed between 12 and 14 weeks of pregnancy. Amniocentesis involves taking a sample of fluid from around the fetus and can be performed from 16 weeks. There are times when one test is more appropriate than the other and the doctor performing the test can provide advice about which test is most suitable.
CVS and amniocentesis are safe procedures although both carry a small (less than 1%) risk of miscarriage and are therefore only performed when there is a potential benefit. Our Maternal Fetal Medicine Specialists are all highly experienced in these procedures.
The time to receive results after CVS or amniocentesis depends on the specific tests required and varies between 48 hours and two weeks. Occasionally, for very specific testing, the turnaround time for results may be longer. We will be able to provide an expected time frame at the time of your test.
We require confirmation of your blood group if you are undergoing CVS or amniocentesis. More detailed information will be provided when you book an appointment for these procedures.