Obstetric Scans

Obstetrical Ultrasound

Early Pregnancy Scans (6 to 10 weeks)

Also called the Dating Ultrasound Scan, the purpose of this scan is basically to determine the pregnancy life (confirmation of the baby's heartbeat), number and dating of the pregnancy. At this early stage which is the embryonic phase mainly only very primitive anatomy is appreciated and a transvaginal scan approach is usually necessary. This scan reassures couples that are concerned about miscarriage risk that the pregnancy is alive and the gestational age can be verified.

First Trimester Scans - For combined screen (11 to 14 weeks)

This scan is done via the transabdominal approach however a transvaginal scan is often necessary to obtain more detail of the early fetal anatomy. Pregnancy dating and the number of babies are also identified at this time.

The main purpose of this scan is to obtain ultrasound data for the first trimester combined screen which includes the fetal body length, nasal bone appearance and the neck skin thickness (nuchal translucency). The combined screen uses this ultrasound data as well as maternal age and blood levels of specific hormones to assess the individual risk of chromosomal abnormality. The risks are assessed as either low or high. This is a screening test only and as such will detect about 80% of Down sydrome pregnancies.

The highly specialised sonologists and sonographers here at Northern Ultrasound for Women are able to further screen for many major defects in the early developing fetal anatomy. A full anatomical survey is however still recommended for 19 - 22 weeks when the baby has grown and developed adequately for optimal anatomical imaging.

First Trimester Scans - NIPTS Only (13 to 14 weeks)

This scan is done via the transabdominal approach however a transvaginal scan is often necessary to obtain more detail of the early fetal anatomy. Pregnancy dating and the number of babies are also identified at this time.

The purpose of this scan is to similar to the first trimester combined screen as above however the ultrasound data is not required for risk calculation if NIPT (e.g. Percept, Harmony, Generation) has been chosen as the chromosomal screening option.

Having an NIPT such as Percept is far superior to the combined screen for Down syndrome screening (99+% vs. 80%) and a low risk result would be further reassuring against other chromosomal abnormalities. The main emphasis of this scan therefore is to survey the early fetal anatomy.

The highly specialised sonologists and sonographers here at Northern Ultrasound for Women are able to screen for many major defects in the early developing fetal anatomy. A full anatomical survey is however still recommended for 19 - 22 weeks when the baby has grown and developed adequately for optimal anatomical imaging.

Mid Trimester Scans (19 to 22 weeks)

This is referred to as the routine anomaly scan because a screen of the fetal anatomy is performed. This scan is the most time consuming of routine pregnancy scans and is performed via the transabdominal approach with recourse to transvaginal scanning if necessary. The fetal measurements are performed and early growth can be assessed. At this stage there is the opportunity for the parents to appreciate some features such as the facial profile, fingers and toes.

Third Trimester Scans (24 weeks onwards)

These scans are performed as directed by the obstetrician in cases where fetal growth, a specific anatomical region or the placental site needs review. The fetal weight is estimated from standard fetal measurements. Assessment includes liquor volume and the parameters of wellbeing such as the cord blood flow pattern.