The benefits of complete information on request forms for antenatal screening for Down syndrome and other conditions

Front Cover of Antenatal screening for Down syndrome and conditions consumer resource
For high quality risk results, all sources of information are essential.
Antenatal screening for Down syndrome and other conditions gives women a risk result based on information provided from different sources.

These sources include:

  • the request form 
  • maternal serum
  • a nuchal translucency ultrasound scan (for first trimester screening only).

To ensure high-quality risk results, all sources of information are essential. 

The screening laboratories (LabPLUS at Auckland District Health Board and Canterbury Health Laboratories at Canterbury District Health Board) have been reviewing the information provided on the request forms and what the impact of missing information may be.

The laboratories have reviewed request form data from August and September 2013, which constituted over 7000 request forms.

Table 1 shows the volumes and percentage of the data most often missing from request forms.

Although the overall percentage of missing information is small, a total of 955 request forms had more than one piece of information missing, which affects the quality of the risk calculation.

There are some data items that are essential to the risk calculation, including IVF details and pregnancy dating. If these items are not provided, a risk cannot be issued and the screening laboratory therefore rings the referring practitioner for this information.

For other information that is missing on the request form, including weight, previous history and smoking status, a default value will be used. This may lead to inaccurate results. For example, the default for weight is 65kg and if the woman is well over or under this weight, the risk calculation will not be as accurate as it could be and therefore the results are suboptimal. Within this data, supplied weights were between 38 and 173kg.

The screening laboratories issue hard-copy risk results for this screening. The National Screening Unit (NSU) strongly recommends practitioners review the information within the risk reports. The screening laboratories are more than happy to answer any queries or make any changes to risk calculations if practitioners provide updated information.

Table 2 provides more information on the impact of missing information.

Page 54 of the practitioner guidelines also have more information on the impact of accurate information.

Table 1: Volume and percentage of data most often missing

Request form information item Number of missing items Percentage of missing items
Ethnicity 468 6.5
Weight 436 6.1
Smoking status 233 3.2
NHI 151 2.1


Table 2: Impact on the risk calculation from missing data items

 Information  Rationale
Weight Smaller women have higher serum analyte levels and larger women have lower serum analyte levels. This has a significant impact on the risk calculation. The default if not provided is 65kg.
Smoking Smoking affects placental function and serum analyte levels. The default if not provided is non-smoker.
Ethnicity Serum analyte levels alter with different ethnicities. The default if the information is not provided is European.
NHI NHI ensures the right woman is linked to the right result and sent to the right health practitioner.


Screening laboratories contacts:

For Taupo north please call 0800 LABLINK.
South of Taupo, please call 0800 THELAB.




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Page last updated: 13 December 2013