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Ultrasound (Prenatal)

Our department provides basic and subspecialized obstetrical ultrasound services to expecting families from all of  British Columbia and the Yukon.
Care provider FAQ

Current practice in British Columbia is to date the pregnancy according to the earliest ultrasound performed where the crown rump length (CRL) measurement measures at 10mm or greater, unless conception date is known from timed ovulation induction (Ovulation induction or in vitro fertilization -IVF), as per PSBC Ultrasound standards and SOGC Guideline No 388.

Dating by BCW ultrasound may differ slightly from that obtained through different ultrasound units if a different chart for first trimester crown rump length was used.

The Robinson CRL chart currently used can be found here.

Estimated due date and gestational for a given date can be calculated based on dating ultrasound date and gestational age for corresponding CRL using PSBC Pregnancy Dating Tool

Soft markers of aneuploidy are routinely assessed as part of routine detail ultrasound from 17 weeks to 22 weeks 6 days gestational age unless:

  • NIPT was performed earlier in the pregnancy or is planned ‎**
  • A Genetic amniocentesis or chorionic villus sampling has been performed 
  • The ultrasound requisition specifies that "examination of soft markers is declined by the patient"  
Soft markers are assessed and reported as per PSBC Guideline . A link to the PSBC Trisomy 21 risk calculator can be found here.

**As of  November 16 2020, the presence of a nasal bone, Nuchal fold thickness, fetal bowel echogenicity and renal pyelectasis are routinely assessed at the time of detail scan in all patients regardless of NIPT testing result.

‎The fetal nuchal region is assessed as part of the 11-14 weeks GA examination. NT measurement is however not reported for the purpose of aneuploidy risk calculation in pregnancies where NIPT or PGT-A was already perfomed. 

Please see MEMO.


Due to limited capacity, booking guidelines for pregnancies complicated by diabetes have been implemented.

Please also see explanatory notes in previously circulated Memo ‎

Placental cord insertion is routinely assessed as part of fetal anatomical detail examinations.

Findings and recommendations are reported according to to our local Abnormal placental cord insertion guideline.‎

‎Irregularly irregular fetal arrhythmia is a common and typically benign finding on routine fetal heart auscultation. 

The following MEMO outlines an initial approach for careproviders when an irregular fetal arrhtymia is detected.  

BCW  ultrasound schedule and explanatory notes for low lying placenta and placenta previa


Referral pathway for fetuses with small Head Circumference (HC) or Biparietal Diameter (BPD)‎


Specialized exams

Criteria for referral for subspecialized obstetrical examinations are described below.

 Referral criteria for NT exam are as per PSBC Guidelines.

Number of available slots are limited. If the booking is declined, other sites offering NT exam can be found here 


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Endovaginal cervical length assessment is typically performed serially in "at risk patients" between 16 and 24+0 weeks GA. 

Frequency (usually every 1-2 weeks) depends on measurement obtained and the nature of risk factors


Indications for endovaginal (EV) cervical length assessment include:

  • Previous history of preterm birth <36 weeks GA
  • Previous LEEP or cone biopsy 
  • Follow up of EV cervix length <25mm in current pregnancy and gestational age < 24+6 weeks GA 
  • Maternal history of connective tissue disease (eg Ehler Danlos)
  • Maternal history of uterine malformation (eg unicornuate uterus)
  • Cerclage placement confirmation:
    • done once <24+6 weeks GA following procedure
    • follow up EV ultrasound only if clinical concern of cerclage failure  

Referral for other indications (such as admission for signs/symptoms of preterm labour) are triaged at the discretion of the BCW ultrasound reporting physician

This assessment is performed between 20 and 24+0 weeks gestational age in singleton pregnancies meeting eligibility critria outlined in the risk assessment form as part of the MFM EMMA clinic referral.

All EMMA referrals are triaged by MFM. When deemed appropriate or when requested by careprovider, an ultrasound-based consult may be provided as part of the ultrasound report in lieu of a separate MFM clinic consult. 

When an ultrasound-based EMMA consult is requested:

1. Referral through MFM is required for booking the ultrasound examination

2. Recommendations are outlined in the ultrasound report following the ultrasound examination.

3. It is the responsibility of the referring care provider to review the content of the report with the patient.

4. When abnormal or unexpected findings are found at the time of ultrasound, the referring careprovider is notifified and the patient may be seen in consultation by MFM. 

‎Referral criteria for specialized heart exams are listed here.  Please specify indication on referral form.

Referrals for abnormality detected on a prenatal ultrasound exam are invited to an FDS clinic appointment. 

Referral criteria for the FDS clinic can be found here

Referral for abnormalities not listed under FDS clinic are triaged accordingt to the BCW Ultrasound triage guidelines.

BCW most recently updated umbilical artery Doppler protocol can be found here

Umbilical artery Doppler studies are routinely performed when:

  • Fetal abdominal circumference measures less than the 10th percentile for gestational age in singleton or multiple pregnancies
  • In pregnancies complicated by pre-eclampsia or gestational hypertension
  • at MFM request (eg complex monochorionic twins)
  • Other indications: are triaged and performed at the discretion of reporting MFM physician.

Middle cerebral artery Doppler (MCA) is routinely used for screening for severe anemia in the at risk fetus such as:

1. Kell alloimmunization (any antibody titer)

2. Anti-D or other significant antibodies alloimmunization, when critical titer is reached as per Canadian Blood services recommendations.

3. Fetal maternal hemorrhage documented by positive Kleihauer test.

4. As part of screening for TAPS in select cases of Monochorionic twins.

Women should be referred to the MFM clinic when the fetus is identified to be at risk for severe fetal anemia due to alloimmunization.

MCA Doppler studies may be performed for other indications, at the discretion of MFM.

All requests for Middle cerebral artery Doppler are triaged by the reporting MFM‎ physician.



Technical protocols

BCW checklist for image acquisition and interpretation‎


BCW Umbilical artery Doppler Protocol update *2024*


Protocol and explanatory notes for BCW ultrasound examination schedule for monochorionic pregnancies‎


Follow up recommendations for PLSVC


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SOURCE: Ultrasound (Prenatal) ( )
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