Prenatal Genetics

There are many reasons why a genetics referral may be made during a pregnancy. Some individuals/families are aware of a family history of a genetic condition. Other individuals/families may learn of an increased chance for a genetic condition based on screening results and/or ultrasound findings during their pregnancy.   

Some commonly seen indications in prenatal genetics include:   

  • Positive prenatal screening results (e.g. FTS, MSS, NIPT)  

  • Advanced maternal age (>40 years or older at delivery)  

  • Family history of a known genetic condition and/or couple are confirmed carriers of the same genetic condition  

  • Ultrasound findings (e.g. soft markers, anomalies)  

  • Twin pregnancies  

For Patients   

What to Expect  

During your genetic counselling appointment, we will take a detailed pregnancy and family history, discuss the reason for referral, what it could mean for you and your baby, and discuss available testing options. There are many testing options available, some are more invasive than others. We will discuss the pros and cons of all available options. Not all people seen in the genetics clinic prenatally choose to do further testing. We will ensure you only proceed with a testing plan that you are comfortable with.  

Some individuals/families wish to pursue genetic testing during a pregnancy to gather information to prepare themselves, their relatives, and their healthcare team to welcome a baby with a genetic condition. Other individuals/families seek this information because it would impact their decision about continuing a pregnancy. We are here to provide support and guidance regardless of your decisions surrounding pregnancy management.

For Providers  

To be seen by our clinic in a pregnancy, a referral from a healthcare provider is required. This could come from a family doctor, OB, midwife, Nurse Practitioner or even a walk-in clinic if needed.  

A copy of our referral form can be found here: Genetics Clinic Referral REFG0010 

What should be included with a prenatal genetic referral?  

  • Dating ultrasound (mandatory) 

**Ultrasound confirmation of pregnancy dating is required with ALL prenatal referrals. Any prenatal referral received without a dating ultrasound will be declined and may result in a delay in appointment scheduling**  

  • All ultrasounds from the current pregnancy  

  • Prenatal bloodwork (CBC, type and screen, Hb electrophoresis, etc.)  

  • Antenatal records  

  • Prenatal screening reports (FTS, MSS, NIPT)  

  • Relevant family records if referring for positive personal/family history  

In order to offer genetic testing for a particular familial condition, we need a copy of the affected relative’s genetic testing report. Including this report in the referral helps to avoid delays in care.    

Why was my prenatal genetic referral declined?   

Common reasons include:   

1. Referral received without a dating ultrasound or relevant records for indication                 

  • Send a new referral with all relevant supporting documentation.  

2. Patient lives outside of our catchment area   

  • Send your referral to a genetics clinic closer to the patient’s home address. A list of genetic clinics in Ontario can be found here.

3. Weight adjustment not completed on positive prenatal screening report   

  • Request a weight adjustment. Fax the prenatal screen back to the lab indicating the patient’s approximate weight when the bloodwork was done. If the amended screening report remains positive, consider sending us a new referral.  

4. Suspected hemoglobinopathy carrier status without molecular confirmation  

5. Referred for increased aneuploidy risk (e.g. advanced maternal age, positive prenatal screen) and NIPT has already been ordered 

  • Only re-refer the patient if the NIPT is abnormal (i.e. high risk, atypical, or no result) OR if the patient wishes to discuss diagnostic testing  

6. Referred for advanced maternal age but patient is under age 40 years at delivery 

  • Arrange routine prenatal screening or self-pay NIPT (additional information below). Re-refer if there are any abnormal results  

Can prenatal genetic screening/testing be arranged by a non-genetics healthcare provider?   

There are several prenatal testing options that can be arranged by a non-genetics healthcare provider. Having this testing arranged without a referral to genetics may allow for decreased wait times and faster results.   

Primary health care providers (i.e. family doctors, midwives, OBs) can order routine prenatal screening, including FTS and MSS. Family doctors or OBs can order OHIP-funded Non-Invasive Prenatal Testing (NIPT) without first referring to genetics for the following common indications:  

  • Advanced maternal age (>40 years at delivery)   

  • Positive prenatal screen (e.g. FTS, MSS) with nuchal translucency measurement <3.5mm  
    **If the NT measurement is >3.5mm, a referral to genetics is preferred** 

  • Previous pregnancy/child with trisomy 13, 18, or 21 when parental karyotypes have been done and are normal  

  • Ongoing twin pregnancy  

A referral to genetics can be made if the NIPT results are abnormal or the family wishes to discuss diagnostic testing options (i.e. chorionic villus sampling or amniocentesis).    

Additionally, you may consider discussing carrier screening options with patients from the following higher risk populations: 

  • Individuals of Asian, Mediterranean, Middle Eastern, Caribbean, South Central, or African descent have a higher chance of being carriers of hemoglobinopathies (e.g. sickle cell disease, thalassemia). You can arrange initial screening with a complete blood count, hemoglobin electrophoresis, and ferritin. Confirmatory molecular testing can subsequently be arranged if these initial results show any concern that your patient may be a carrier.  

  • There is also specific carrier screening available for Ashkenazi Jews, certain French Canadians and certain Indigenous populations. Joint SOGC-CCMG Opinion for Reproductive Genetic Carrier Screening is available here.

Below are indications we currently do not see in our clinic:  

  • Teratogenic prenatal exposures  

  • Personal and/or family history of conditions with non-genetic or complex/multifactorial cause  

  • Isolated history of multiple miscarriages (primary care physician should arrange chromosome testing on the couple and refer if there are concerns)  

  • Isolated finding of certain soft markers, including chorionic plexus cysts, intracardiac echogenic focus, or two vessel cord, when prenatal screening is negative and maternal age is <40 years  
    **For isolated two vessel cords, we recommend obstetric and ultrasound follow up with re-referral if additional concerns are found on fetal anatomy** 

If you are a healthcare provider questioning whether a referral to genetics is warranted for an ongoing pregnancy, please contact us at 905-433-2733 for guidance.  

Additional Resources