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  • What We Screen For In Ontario
    • Trisomy 21 (Down Syndrome)
    • Trisomy 18 (Edwards Syndrome)
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    • Less than 14 Weeks' Pregnant
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    • Twins and More Than Two Babies
    • Vanishing Twins
  • Results and Next Steps
    • Enhanced First Trimester Screening Results
    • Second Trimester Screening Results
    • Screening for Vanishing Twins Results
    • Non-invasive Prenatal Testing (NIPT) Results
    • 11-14 Week (Nuchal Translucency) Ultrasound Results
    • 18-22 Week Ultrasound Results
    • Diagnostic Testing
  • For Providers-How to Order
    • enhanced First Trimester Screening (eFTS) Guide
    • Second Trimester Screening (STS) Guide
    • Non-Invasive Prenatal Testing (NIPT) Guide
    • Screening for Vanishing Twins Guide
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HomeFor Providers-How to OrderScreening for Vanishing Twins Guide
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pregnant belly

Screening for Vanishing Twins Guide

Nuchal Translucency and Second Trimester Screening (NT + STS) is a screening test for trisomy 21 and trisomy 18 consisting of a nuchal translucency ultrasound in the first trimester. The blood work for this test is only done in the second trimester of pregnancy, not on the day of the ultrasound.

This test is offered mainly to individuals who have a singleton pregnancy following a vanishing twin / co-twin demise.

Step-by-step instructions are outlined below to provide guidance to health-care providers for how to order this test in Ontario.

It is important to know that enhanced First Trimester Screening (eFTS) and Non-Invasive Prenatal Testing (NIPT) are not possible for "vanishing" twin pregnancies.

Step 1 |


Complete the Multiple Marker Screening Requisition

Multiple Marker Screening (MMS) is done by three provincial laboratories: Trillium Health Partners - Credit Valley Hospital, Mount Sinai Hospital and North York General Hospital. Check out our interactive map to learn which of the three requisitions you should use. 

screenshot of MMS req NYGH
North York General Hospital Requisition
screenshot MMS req THP
Trillium Health Partners - Credit Valley Hospital Requisition
screenshot MSH
Mount Sinai Hospital Requisition

The Multiple Marker Screening Requisition must be completed in full prior to NT ultrasound. Please note that missing information decreases the quality of the screen and can potentially delay the results.

Demographics Section

The pregnant individual’s name, date of birth, health card number, address, and phone number should be completed.

"Test Requested" Section

Check off the "NT + Second Trimester Screening" option and fill in the date of the STS blood draw.

  • NT+ STS is available to individuals who had a "vanishing twin"/co-twin demise identified prior to the NT ultrasound. This test may also be available to individuals who had a NT ultrasound, but missed the time window for the eFTS bloodwork. 
  • The nuchal translucency (NT) ultrasound is only available when the crown-rump length measurement (the measurement of the length of embryo from top of the head to the bottom of the torso) at the time of the ultrasound is between 45 and 84 mm. This corresponds to a gestation between 11 weeks 2 days to 13 weeks 3 days gestation, based on published charts of Hadlock and Daya1.
  • An STS blood sample is needed between 14 weeks 0 days and 20 weeks 6 days gestation. However, the blood sample cannot be drawn until 8 weeks after the demise. Based on the estimated date of demise, calculate the date after which the pregnant individual can have their blood drawn. Write this date in the space provided in the “STS + NT” section.

Example calculation:

If the demise was estimated to have occurred at 10 weeks 0 days, the pregnant individual could have the STS blood draw after 18weeks 0 days (and up to a maximum of 20 weeks and 6 days).

1The Multiple Marker Screening labs determine the gestational age based on the published tables of Hadlock and Daya.

  1. Hadlock, F.P., Deter, R.L., Harrist. R.B., Park, S.K. (1982). Fetal biparietal diameter: a critical re-evaluation of the relation to menstrual age by means of real-time ultrasound. J Ultrasound Med 1(3):97–104. DOI: 10.7863/jum.1982.1.3.97
  2. Daya, S. (1993) Accuracy of gestational age estimations by means of fetal crown-rump length measurement. Am J Obstet Gynecol 168(3 Pt 1):903–8. DOI: https://doi.org/10.1016/S0002-9378(12)90842-X

 "Clinical Information" Section

Accurate and complete information in this section will increase the quality  of the screening results by reducing the chance of false positives and false negatives. 

Example of statement you can make when speaking with pregnant individuals:

I have some questions about you to ask to make sure your screening is as accurate as possible.

Racial Origin of Oocyte
 

Indicate the racial origin of the oocyte (egg) provider, which is usually the pregnant individual. In cases of egg donation, indicate the racial origin of the oocyte (egg) provider, not that of the pregnant individual.

Racial origin information is needed because the concentrations of screening markers have been shown to vary depending on the racial origin. Therefore, a pregnant individual’s screening markers are adjusted based on the racial origin information provided.

Only the broad racial origins listed are needed for screening marker adjustment. The categories on this requisition are not inclusive of all the race categories commonly used as social descriptors in Ontario. 

Description / examples for each of the racial origin categories on the requisition:

  • Asian: South Asian (E.g. East Indian, Pakistani, Bangladeshi, Sri Lankan, Indo-Caribbean etc.), East/Southeast Asian (e.g. Chinese, Korean, Japanese, Filipino, Indonesian, Thai) descent
  • Black: African, Afro-Caribbean descent
  • Indigenous: First Nations, Metis, Inuk/Inuit descent
  • White: European, Middle Eastern descent (e.g. Arab, Persian, Afhgan, Egyptian, Lebanese, Turkish, Kurdish)
  • Other: Another race category or mixed racial origin

Racial origin should be as accurate as possible and should reflect the individual’s ancestral background (which may or may not align with how the pregnant individual identifies), not simply their birth country. This information should be obtained directly from the pregnant individual whenever possible.

Example of question you can ask pregnant individuals:

In our society, people are often described by their race or racial background. For example, some people are considered “White”, “Black”, or “South Asian”. How would you identify or describe your racial background?

Weight

Indicate the pregnant individual’s weight, including units (pounds (lbs) versus kilograms (kg)), at the time when this requisition is completed. This information is used for screening marker adjustments. A weight discrepancy of 5 or more pounds (2.3 kilograms) has a significant impact on the risk for trisomy 21 for pregnant individuals with a risk close to the screening cut-off.

Example of questions you can ask pregnant individuals if the weight is not obtained at the time of appointment:

  • What do you think is your current weight? 
  • Do you think the weight your provided is accurate within 5 pounds? 
Last Menstrual Period

The Last Menstrual Period (LMP) is not needed. For NT+STS, the crown-rump length measurement at the time of NT ultrasound will be used instead of the LMP, to establish the gestational age of the fetus and determine the appropriate time for bloodwork in the second trimester.

Insulin-Dependent Diabetes Mellitus History

Indicate if Insulin-dependent Diabetes Mellitus was diagnosed prior to the individual’s current pregnancy. Individuals with insulin-dependent Diabetes Mellitus have been shown to have different concentrations of screening markers compared to those who do not have this diagnosis. Screening marker adjustments must be made to account for these differences.

No screening marker adjustments are made for pregnant individuals with a history of gestational diabetes or preexisting diabetes that is not managed with insulin.

Example of questions you can ask pregnant individuals:

  • Do you have a diagnosis of diabetes? 
  • Was the diabetes diagnosed before the current pregnancy?
  • Do you use insulin to manage the diabetes? 
Cigarette Smoking History

Indicate if the pregnant individual has smoked any amount of tobacco at any point in the current pregnancy. Individuals with a history of smoking tobacco in their current pregnancy have been shown to have different concentrations of screening markers compared to those who do not have this history. Screening marker adjustments must be made to account for these differences. 

If the requisition does not include information about the smoking history, the pregnant individual is considered a non-smoker. Due to lack of published data, pregnant individuals exposed to second-hand smoke are considered non-smokers. 

Example of question you can ask pregnant individuals:

Have you smoked any cigarettes at any point in the current pregnancy?

In Vitro Fertilization (IVF) History

If the pregnancy was conceived using in vitro fertilization (IVF), indicate the egg harvest date and date of birth of the egg donor (either self or non-self). If the egg donor's full date of birth is unknown, indicate the year of birth. If only the year of the donor date of birth is provided, July 1 of the provided year is used as the date.

This information is requested because the age of the egg at the date of delivery influences the screening risk. In addition, screening marker levels vary between IVF and natural conceptions and screening marker adjustments must be made to account for these differences.

Examples of questions you can ask pregnant individuals:

  • Did the current pregnancy happen through in vitro fertilization (IVF)? 
  • What was the egg harvest date?
  • Were your own eggs used for this pregnancy, or was there an egg donor involved? 
  • Do you know the date of birth of the egg donor; at minimum, the year of birth? 

"Ultrasound Information" Section

Be aware that only the sonographer / physician performing the NT scan completes the "Ultrasound Information" section when ordering NT + STS.

 

Step 2 | 


Complete a Nuchal Translucency Ultrasound Requisition


Visit our interactive map to find facilities offering NT ultrasound in Ontario. You can contact the ultrasound facility of interest to obtain the centre-specific ultrasound requisition

image of ultrasound and tech

Step 3 |


Provide Requisitions to the Pregnant Individual

  • Give both the completed nuchal translucency ultrasound requisition and Multiple Marker Screening requisition to the pregnant individual.
  • If your office is booking the NT ultrasound, it is helpful to fax the MMS requisition with the ultrasound requisition to the ultrasound facility. It is important that the ultrasound facility has both of these requisitions at the time of the ultrasound appointment, either from your office or from the pregnant individual.
  • Check if additional requisitions are required by the ultrasound and blood work facilities, such as the Ministry of Health and Long Term Care Laboratory Requisition.

woman holding a form

Step 4 |


Provide Step-by-Step Instructions to the Pregnant Individual

  • Provide clear instructions to the pregnant individual for how to navigate the different steps involved in obtaining NT + STS. Please note that Prenatal Screening Ontario does not organize prenatal genetic screening tests.
  • If the pregnant individual misplaces it after the NT ultrasound, another copy of the completed Multiple Marker Screening requisition (including the ultrasound section) must be obtained from the ultrasound facility, whenever possible. Contact Prenatal Screening Ontario or the Multiple Marker Screening lab to discuss options if a completed Multiple Marker Screening Requisition cannot be obtained. 
leaflet with instructions for how to order screening for vanishing twins
Share with Pregnant Individuals: How to Get Prenatal Screening for Vanishing Twins

 

 

 

Step 5 |


Obtain Report and Check for Accuracy

  • Results will be reported to you by the MMS lab generally within 5 business days after the receipt of the blood sample. It is important to take into account the time lag that can occur between the time when the report is ready and when it is received by your office.
  • If you do not receive the prenatal screening report, we encourage you to follow up with the MMS lab directly. Prenatal Screening Ontario does not have access to screening results of individuals. 
  • Review the screening report for accuracy. If any errors or omissions are noted, contact the MMS Laboratory to determine if an amendment to the report is needed.

When is a Report Amended?

A report is considered “amended” if changes are made after the report has been issued to the health-care provider. Amending reports is necessary to correct errors that include data being inaccurately provided on the requisition. Some examples are inaccurate racial origin identification, inaccurate diabetes status, and correction of weight, due to either wrong units (i.e. pounds or kilograms) or difference in weight of more than 5 - 10 pounds (2.3 - 4.6 kilograms)1 from that given on the requisition.

1North York General Hospital and Mount Sinai Hospital labs will amend a report if there is a difference in weight of more than 10 pounds. The Trillium Health Partners lab will amend a report if there is a difference in weight of more than 5 pounds. 

How is a Report Amended?

Health-care providers can write the amendment(s) directly on the screening report and fax it back to the Multiple Marker Screening Laboratory, indicating that an amendment is required as per the enclosed report. Alternatively, the health-care provider can fax a note with the pregnant individual's name, date of birth, health card number, and details related to the amendment request, including relevant clinical information. 

Step 6 |


Communicate Results and Next Steps

  • Once the report is received, results should be communicated in both “screen positive” and “screen negative” scenarios, including the specific risk estimate provided on the report.
  • Ensure continuity of care: forward the report to any other providers involved in the care of the pregnant individual.

The results of the nuchal translucency ultrasound will be sent separately by the ultrasound facility. If the nuchal translucency measurement is increased (3.5 mm or above), inform the pregnant individual of this result as soon as possible and offer a referral for genetic counselling irrespective of the eFTS results

screenshot of how to discuss results leaflet
Point-of-Care Tool: How to Discuss Multiple Marker Screening Results
  • For Providers-How to Order
    • enhanced First Trimester Screening (eFTS) Guide
    • Second Trimester Screening (STS) Guide
    • Non-Invasive Prenatal Testing (NIPT) Guide
    • Screening for Vanishing Twins Guide

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