Ultrasound is used to assess the health and development of the baby throughout pregnancy. Your doctor will discuss with you which examinations are needed in your pregnancy. Doppler ultrasound is used to look at blood flow in structures such as the heart and umbilical cord.
3 and 4D Ultrasound imaging may be used in all pregnancy ultrasound examinations. It can be helpful in diagnosis and provide very life-like pictures of your baby. The best images are obtained during the late pregnancy ultrasounds when they are most baby like in appearance.
Not everyone finds 3D images appealing. In the first half of pregnancy the image of the face can be quite skeletal in appearance.
The quality of all ultrasound images is affected by the position of the baby, the amount of fluid around the face and other maternal factors. We will always strive to provide the best images of your baby.
A DVD is provided for all pregnancy ultrasounds. It provides a medical record of the examination as well as images for your enjoyment.
There are four types of pregnancy ultrasound
- Early pregnancy (before 11 weeks)
- 11-14 weeks with Down Syndrome screening
- 20 weeks
- Late pregnancy
Early Ultrasounds are performed to check all is well with the pregnancy and when it is due. Bleeding and pain are the commonest reasons for an early pregnancy ultrasound. One in four women experience bleeding in pregnancy, some will miscarry but most will not. Ultrasound can diagnose miscarriage or provide reassurance that all is well. Other thing s which may be found at this time are twins, ectopic pregnancy, ovarian cysts and fibroids.
Most early pregnancy ultrasounds are performed with external and internal/vaginal approaches. The small internal vaginal scanner causes less discomfort than a smear test examination. It almost always gives clearer and more accurate information about early pregnancy development.
This is the most important ultrasound in pregnancy. Most 11-14 week pregnancy ultrasounds are performed with external and internal/vaginal approaches. The small internal vaginal scanner causes less discomfort than a smear test examination. It almost always gives clearer and more accurate information about this stage of pregnancy.
There are three major objectives
- To confirm the due date
- To check the organs of the baby are developing normally.
- To determine the risk for Down Syndrome.
The traditional way the due date is worked out is based on the menstrual cycle. This is inaccurate 20% of the time. All babies are the same size in the first half pregnancy so the size can be used to accurately establish the age of the baby and the due date.
At 12 weeks all the organs of the baby are formed and can be examined. Reassurance that all is developing normally can be given and in a very small number of cases (approximately 1%) abnormalities of the baby may be diagnosed. (see also 20 week ultrasound).
Down Syndrome is a genetic condition associated with intellectual and physical disabilities. It is possible to diagnose or rule this condition out with certainty using Chorion Villus Sampling (CVS) or Amniocentesis (see CVS / Amniocentesis). There is a small risk of miscarriage due to these tests (1 in 200) so they are usually only chosen if an increased risk for Down Syndrome has been identified. The risk for Down Syndrome is worked out by adding the risks associated with age, a 10 week blood test and the ultrasound.
The chance of having a baby with Down Syndrome increases with maternal age as shown on the following table.
Maternal age related risks of having a live born child with Down syndrome and the risk of carrying an affected fetus at 12 weeks of pregnancy.
Your doctor will order a blood test at 10 – 11 weeks which measures 2 proteins in your blood stream. In Down Syndrome pregnancies one is very high and the other low. Based on the blood test measurements a risk for Down Syndrome can be calculated.
Most (80%) of Down Syndrome fetuses at the 11 – 14 week ultrasound have an increased skin thickness on the back of the neck (nuchal translucency). The thicker the skin the greater is the risk.
On the day of your visit to Melbourne Ultrasound for Women, once the scan has been completed the measurements are faxed to a central laboratory which analyses all the 10 –11 week blood samples. In most cases the combined result adding the risks of age, ultrasound and blood test will be available within 30 minutes of the ultrasound We encourage you to wait to receive the results on the day but we can contact you later that day if you wish. Further testing for Down Syndrome CVS or Amniocentesis is usually considered if the risk is more than 1 in 300 (eg 1 in 100 or 1 in 50). Most women who have an increased risk will not have a baby with Down Syndrome. Women with a low risk may still have a baby with Down Syndrome although this is rare.
This ultrasound is to check organ development in detail. Some organs such as the heart, lips and palate, lower spine and digits are too small to check at 11 – 14 weeks. A detailed examination of all structures visible on ultrasound will be performed. In almost all cases reassurance will be given that the anatomy as seen on ultrasound is developing normally. Very small abnormalities such a hole in the heart or cleft lip may not be seen even with the best equipment and skill. Some abnormalities may develop later in pregnancy conditions such as autism and cerebral palsy cannot be diagnosed using ultrasound as there is no visible abnormality. If an 11 – 14 week ultrasound has not been performed the due date can be worked out at this examination.
Down Syndrome Screening cannot be performed using ultrasound at 20 weeks.
The position of the placenta is checked. 1 in 20 placentas are low at 20 weeks but most move away as the pregnancy grows. 1 in 100 placentas are low at 32 weeks. If the placenta is low at 20 weeks a check is usually done at 32 weeks
Late ultrasounds are performed to assess the growth and health of the baby. Some doctors will order this routinely at around 32 weeks. Others only if there are medical complications such as bleeding or where there is a suspicion that the baby is smaller or larger than expected. The weight of the baby can be estimated from the measurements taken at this time and the health is assessed by measurement of the amount of fluid around the baby (amniotic fluid index), the movements of the baby and measurements of blood flow between the placenta and baby (umbilical artery blood flow studies). The lie of the baby is assessed (either head up or head down) and the anatomy is checked again. The placenta position is assessed.
Often in late pregnancy images of the baby are not as clear as that at 12 and 20 weeks. Often the baby is face down and other structures tend to be obscured by the limbs.