20 Week Scan / Detailed Anomaly Scan

The 20 Week Scan or anomaly scan as it is sometimes called is ideal for those parents looking for reassurance or as a secondary option when an earlier screening test has not been performed. Furthermore, it provides an added opportunity to assess the baby’s well being and encourage further bonding.

Detailed Anomaly Scan Checks

Your baby’s internal organs are examined in cross-section which may be difficult for you to make out. Bones appear white, fluid is black and soft tissues may seem to be varying degrees of grey. At this time we will examine changes in the normal anatomy that may indicate an abnormality.

The baby’s head is examined for shape and size. Internal structures such as the ventricles of the brain and cerebellum are examined. The sonographer will do standard measurements and look at the baby’s lips and nose for any obvious defects.

The spine is assessed in both long and short axis views to make sure that all of the vertebrae are in alignment and that the skin is closed. The baby’s abdominal wall is checked at this time too to make sure that all abdominal organs are in their correct position. 90% of all abdominal wall and spine defects can be picked up by ultrasound.

The chest is assessed to view the lungs and the position of the heart. At Ultrasound Dimensions we are concerned with raising the standard of detecting a baby with a possible heart defect. The first step in improving care of “heart babies” is improving the detection of heart disease before birth. The “5 Transverse Views” is a practical and proven way to screen for heart disease at the routine “20 week” scan set up by the Tiny Ticker organization, a national charity in the UK.

The kidneys, stomach, and bladder are also imaged. The baby swallows some of the amniotic fluid that it lies in and so some of that fluid will be seen as a black bubble in the stomach and the urinary bladder as well. Yes, the baby has a wee inside about every half hour so the urinary bladder fills and empties during the scan.

Baby’s legs, arms, hands, and feet are examined. The umbilical cord is assessed to count the number of vessels.

The placenta will be documented to lie at the fundus or anteriorly or posteriorly and to ensure that the placenta does not cover the cervix (the opening of the womb).

There should be enough amniotic fluid at this stage to allow the baby to move around freely.

The routine measurements that are taken include Biparietal diameter of the head (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL). These measurements will have an accuracy of approximately one to two weeks plus or minus the baby’s true gestational age. We consider your baby’s measurements normal if they fall within that range. Not all babies in the womb are exactly the same size because parents aren’t the same size and babies are unique to their parents.

Disclaimer:

The anomaly scan is the best and most detailed scan we have available for the assessment of foetal development. However, not all abnormalities can be detected. There are many things that can affect how well we see the structures of the baby. These can include the position and age of the baby, the amount of fluid around the baby, the type of body tissue you have, your own body weight and if there is scar tissue from previous abdominal surgery such as a Caesarean. In addition to this, some foetal abnormalities are not visible at the time of the scan or they don’t develop until much later (>24 weeks). Problems such as cerebral palsy or learning disabilities like autism are not detected as they are not associated with visible structural differences. In a small number of cases, babies are born with abnormalities, even though no problem was identified by the scan.

It must be understood that ultrasound does not have 100% diagnostic accuracy. There is no diagnostic test in medical practice however diligently performed which is free from false-negative findings. It must be emphasized that although many malformations can be identified during the systematic evaluation of the fetus during the second-trimester anomalies survey, it is well-established that some anomalies may be missed even with the best ultrasound equipment in the hands of highly experienced and well-trained professionals. 1

1. Salomon LJ, Alfirevic Z, Berghella V, Bilardo C, Hernandez-Andrade E, Johnsen SL, et al. Practice guidelines for performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2011;37:116–26.

Anomaly Scan Procedure

At Ultrasound Dimensions, our anomaly scan procedure Includes:

• Ultrasound exam
• Medical obstetric ultrasound report
• Glossy picture print

Please note for twins there is an additional fee of €70.00

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Take a detailed look at how we perform the 20 Week Pregnancy Scan: