Things to keep in mind:
- Informed choice – before ordering the test, discuss benefits, risks and limitations.
- Autonomy – the patient should choose whether to have prenatal screening.
- What prenatal screening options are available in your area?
- What option is most suitable for your patient?
- Which test will provide the optimal care for your patient?
- A screening test is not diagnostic.
The following recommendations are from:
SOGC Clinical Practice Guideline: Prenatal Screening for Fetal Aneuploidy in Singleton Pregnancies. J Obstet Gynaecol Can 2011;33(7):736–750.
- All pregnant women in Canada, regardless of age, should be offered, through an informed counselling process, the option of a prenatal screening test for the most common clinically significant fetal aneuploidies in addition to a second trimester ultrasound for dating, assessment of fetal anatomy, and detection of multiples.
- Counselling must be non-directive and must respect a woman’s right to accept or decline any or all of the testing or options offered at any point in the process.
- Maternal age alone is a poor minimum standard for prenatal screening for aneuploidy, and it should not be used a basis for recommending invasive testing when non-invasive prenatal screening for aneuploidy is available.
- Invasive prenatal diagnosis for cytogenetic analysis should not be performed without multiple marker screening results except for women who are at increased risk of fetal aneuploidy (a) because of ultrasound findings, (b) because the pregnancy was conceived by in vitro fertilization with intracytoplasmic sperm injection, or (c) because the woman or her partner has a history of a previous child or fetus with a chromosomal abnormality or is a carrier of a chromosome rearrangement that increases the risk of having a fetus with a chromosomal abnormality.
- First trimester nuchal translucency should be interpreted for risk assessment only when measured by sonographers or sonologists trained and accredited for this service and when there is ongoing quality assurance, and it should not be offered as a screen without biochemical markers in singleton pregnancies.
- For women who undertake first trimester screening, second trimester serum alpha fetoprotein screening and/or ultrasound examination is recommended to screen for open neural tube defects.
- Timely referral and access is critical for women and should be facilitated to ensure women are able to undergo the type of screening test they have chosen as first trimester screening. The first steps of integrated screening (with or without nuchal translucency), contingent, or sequential screening are performed in an early and relatively narrow time window.
- Ultrasound dating should be performed if menstrual or conception dating is unreliable. For any abnormal serum screen calculated on the basis of menstrual dating, an ultrasound should be done to confirm gestational age.
- The presence or absence of soft markers or anomalies in the 18- to 20-week ultrasound can be used to modify the a priori risk of aneuploidy established by age or prior screening.
- Information such as gestational dating, maternal weight, ethnicity, insulin-dependent diabetes mellitus, and use of assisted reproduction technologies should be provided to the laboratory to improve accuracy of testing.
There are a number of other guidelines which can be found on the SOGC website:http://www.sogc.org/index_e.asp. A number of these guidelines can be found as hyperlinks below:
a) SOGC Clinical Practice Guideline: Prenatal Screening for and Diagnosis of Aneuploidy in Twin Pregnancies. J Obstet Gynaecol Can 2011; 33(7):754–767.
b) SOGC Clinical Practice Guideline: Obstetrical Complications Associated with Abnormal Maternal Serum Markers Analytes. J Obstet Gynaecol Can 2008;30(10):918–932.
c) SOGC Clinical Practice Guideline: Pre-conceptional Vitamin/Folic Acid Supplementation 2007: The use of folic acid in combination with a multivitamin supplement for the prevention of neural tube defects and other congenital anomalies. J Obstet Gynaecol Can 2007;29(12):1003–1013.
d) SOGC Clinical Practice Guideline: Fetal Soft Markers in Obstetric Ultrasound. J Obstet Gynaecol Can 2005;27(6):592–612.