Ken Seethram, MD, FRCSC, FACOG (biography and disclosures)
What I did before
Previously, my practice in prenatal screening revolved around second trimester serum and sonography to identify markers in maternal serum, or ultrasound that would hint at a genetic problem. If these were identified, I would offer patients invasive testing such as amniocentesis.
What changed my practice
The European experience (especially the U.K.) shows that multiple ultrasound markers, serum, and anatomical survey of the fetus can be conducted in the period around 12 weeks, and that this information is much stronger in detecting genetic syndromes than 2nd trimester markers. These first trimester markers include ultrasound screening for nuchal (neck) translucency, nasal bone, ductus venosus (a new marker), and serum for genetic screening. Over 40 countries now do first trimester screening routinely in pregnancy. The North American experience has been stunted by patent disputes, and politics, but recently has revolved around combining first and second trimester markers (known as Integrated Pregnancy Screening, IPS). When set up as a contingency screening model, the literature suggests IPS detection rates are in the 87-88% range. Using a combination of first trimester markers i.e. NT (1992), serum pregnancy associated placental protein A (PAPP-A) and free beta hCG (1995), Nasal bone detection (2003), heart rate, and Ductus Venosus (2009) the overall detection rate for aneuploidy is 96% with a screen positive rate of 3%,
The largest drawback to IPS is that the reporting occurs in the second trimester, when women are starting to feel the baby move, and are developing a greater bond to the pregnancy. Several studies have shown that more than 85% of women prefer early screening (FTS). The FTS protocol is standard in most of Alberta and Ontario. In BC however, FTS is not insured, and with the complete markers, costs around $500.
What I do now
Although I continue to do second trimester anatomy scans and amniocentesis, a large part of my practice is the undertaking of first trimester screening. I also actively advocate for increased awareness regarding screening options. One of the most difficult things in my practice is trying to counsel patients regarding their options, and rates of detection, and then counsel regarding results. It is important to disclose to patients all the options available for screening – not every woman given the option to do more advanced screening will do it. For FTS, serum must be done at 10-11w and the sonogram at 12w (range 11=14w) for best performance. For IPS, the serum PAPP-A and NT is done at 10-12w, and the remaining serum at 16-20w. Either way, patients should be counseled early.
Integrated screening for Down’s syndrome based on tests performed during the first and second trimesters N Engl J Med 1999;341:461-7 (Read the article)
First-Trimester or Second-Trimester Screening, or Both, for Down’s Syndrome N Engl J Med 2005;353:2001-11. (Read the article)
Ductus venosus Doppler in screening for trisomies 21, 18 and 13 and Turner syndrome at 11–13 weeks of gestation Ultrasound Obstet Gynecol 2009; 33: 512–517 DOI: 10.1002/uog.6330 (Request the article with CPSBC Library)
Prenatal Screening for Fetal Aneuploidy – SOGC CLINICAL PRACTICE GUIDELINE J Obstet Gynaecol Can 2007;29(2):146–161 (Read the article)