Dating scan: is to correctly date the pregnancy. The optimal time to perform this is between 11 and 14 weeks gestation, the CRL is assessed and an EDD given at this stage. A basic anatomy check is performed if after 11 weeks gestation.

If the fetus measures within + or - 7 days of the LMP then dating is by LMP. If the CRL is + or - over 7 days of the LMP the dating is by USS.

If the LMP is not known and the fetus has a CRL that suggests is between 11 to 14 weeks gestation then dating will be by USS. If the pregnancy is after this gestation, then dating is by BPD.

A pregnancy may not be accurately dated after 24 weeks gestation. A serial scan will be required at a 2 week interval to assess the growth velocity of the fetus.

Nuchal scan: This is a scan performed in conjunction with a blood test to determine your risk of chromosomal abnormalities such as Downs Syndrome. A full description of this is available on our page Nuchal scanning (LINK) > This scan is performed between 11 to 13+6 weeks gestation. A basic anatomy check is performed during the scan with a measurement of fetal size.

All women are at risk of having a baby with Downs' syndrome. And all fetuses have a small amount of fluid at the back of their neck called Nuchal Translucency. Using ultrasound we can obtain a measurement of this area, along with using the maternal age and accurate gestational age we can assess the individual risk factor for each women. This is NOT diagnostic. It gives us a risk factor.

It gives us a figure in numbers for example 1 : 250 (1 in 250), we would say that this example suggests that there would have to be 250 women, with the same age, gestation and Nuchal Translucency measurement before one women has a baby with Downs' syndrome.

Gender scan: is when after 20 weeks gestation looking at the gender of the baby.
 
Using ultrasound a female fetus will show three parallel bright white lines within the genital area, or Labia may be seen by the sonographer.

The male fetus will express a round bulbous area within the genital area that is the scrotum and penis. This sometimes can be seen on screen as an appearance similar to a profile of a small snail. 

We will never say that we are 100% sure of gender, as some fetuses can be ambiguous. Gender will be confirmed by the midwife at First Newborn check after birth.

Anomaly scan: can be between 18 to 24 weeks gestation. The optimal gestation is 22 weeks. Ultrasound is a highly effective tool in both screening as well as being used as a diagnostic test for any fetal anomalies.

This is to extensively look at the anatomy of the fetus, using measurement and observation as a guide. This is a detailed scan during which each part of the fetal body is examined.

Special attention is paid to the brain, face, spine, heart, stomach, bowels, kidneys, bladder and limbs.

During this scan the position of the placenta will be identified and documented. If it is indicated that the leading edge is low lying, (less then 5cm away from the internal edge) then a further scan will be booked for when the women is 34 to 36 weeks gestation to assess the migration of the leading edge, (this differs in different hospitals).

The sonographer will also assess the amount of Amniotic fluid that surrounds the fetus. At this gestation it is not generally measured but 'eye balled'.

Well being scan: this scan can be used for a variety of reasons.

Four measurements are performed throughout the fetus, two from the head, one around the abdomen and one measurement from the femur length. This will show us if the growth of the fetus is within the normal range for the given gestation.

The same is assessed for the Amniotic fluid and is expressed in cm, having measured four different pockets or areas of fluid and added then together. However, assessing the AFI (Amniotic Fluid Index) is not an exact science.

During the well being scan, if the sonographer has identified that the growth velocity has slowed then an assessment of the blood flow through the umbilical cord will be performed. This allows the sonographer to report weather the placenta may be compromising the well being of the fetus.

This scan aims to determine the growth and health of the fetus by:

• measurement of the growth of the fetal head, abdomen and femur 
   
• estimation of fetal weight
   
• examination of the movements of the fetus
   
• evaluation of the placental position and appearance
   
• measurement of the amount of amniotic fluid assessment of blood flow to the placenta and fetus