ULTRASONOGRAPHY (ultrasound scan or sonar)

• This is a non-invasive technique, where an image of the fetus is generated through the use of sound-waves.
• It is used to assess the structure and development of the growing baby.
• Ultrasound is both a diagnostic and screening test

When should the test be performed?

• Dating scan (from 4 to 8 weeks)
• First trimester (10.5 to 14 weeks)
• Second trimester (18 to 23 weeks)

What does it detect/measure?

• Number of babies present.
• Gender of the baby (16 to 20 weeks).
• Size and position of baby.
• Heart beat of the baby.
• Amount of amniotic fluid.
• Blood flow from the mother to the baby.
• Structural and non-structural markers (risk indicators).

      Non-structural Markers

Non-structural markers are features that are not definitive but are associated with an increased risk for a birth defect or genetic condition, prompting further assessment.

Nuchal translucency (clear space due to accumulation of fluid at back of baby’s neck)

• Measured from (10.5 to 14 weeks)
• Increased risk if measurement greater than 2.5mm

Nuchal fold 

• Measured during second trimester
• Increased risk greater 5mm (<20 weeks) and 6 mm (>20 weeks)

      Structural assessment (major and minor structural abnormalities)

Structural markers (major and minor markers) are abnormalities that effect function or that form part of a diagnosis for a genetic conditions or birth defect e.g. neural tube defect (spina bifida).

• Major markers: Nasal bone, long bones (thigh and upper arm bones), feet, hands, skull, spine
• Minor markers: Appearance of bowel, heart and brain. 

What are the benefits of ultrasound?

• The test is non-invasive and is safe for mother and baby (no risks or side-effects).
• A normal ultrasound may result in reassurance about your pregnancy.

What are the limitations of ultrasound?

• Affected by the characteristics of the mother, such as ethnicity, weight, timing of conception.
• Ultrasound scan operator bias.

MATERNAL SERUM SCREENING

• Maternal Serum Screening (MSS) measures the level of certain products (proteins) in your blood when you’re pregnant.  
• The proteins are: Papp-A, β-hCG, estriol, inhibin-A and alpha fetoprotein (AFP)
• These products are present in all pregnancies but their levels indicate a risk of particular birth defect and/or chromosomal abnormalities.

When should the test be performed, and what products are tested?

       First trimester – 9 to 13.6 weeks (optimally 9 to 10 weeks)

• Papp-A, β-hCG

       Second trimester – 16 to 20 weeks

• Triple test: β-hCG, estriol, and alpha fetoprotein (AFP)
• Quadruple test: β-hCG, estriol, and alpha fetoprotein (AFP) and inhibin-A

What risks does a maternal serum screen detect?

• Chromosomal abnormalities such as trisomy 21 (Down syndrome), Edwards syndrome (Trisomy 18) and Patau syndrome (Trisomy 13).
• Neural tube defect such as spina bifida.

What are the limitations of the first trimester maternal serum screen?

• Affected by the characteristics of the mother, such as ethnicity, weight and method of conception
• The test is known to have a 5% false positive result - meaning that 1 in 20 women will be told that their pregnancy has an increased risk but there is no additional risk.
• The results are not conclusive as it only detects about 65% of pregnancies with a chromosomal abnormality.  The accuracy can be increased by including the result of other screening tests, such as an ultrasound scan, this is called a combined first trimester screen.

What do the results from the maternal serum screen test mean?

The results are given as a risk that the baby may have a chromosomal abnormality or birth defect in relation to the maternal age risk.

What are the advantages of maternal serum screening test?

• The test is non-invasive and is safe for mother and baby (no risks or side-effects).
• A normal result may provide reassurance about the pregnancy.
• No side-effects.