What is the benefit of adding a nuchal translucency (NT) ultrasound measurement for women 35 years and older?
Although the serum integrated prenatal screen (SIPS) is associated with a high detection rate for Down syndrome, the combination of serum screening and NT (integrated prenatal screen or IPS) reduces the false positive rate.
Who qualifies for NT as part of IPS?
As of March 2011, Serum Integrated Prenatal Screen (SIPS) is available to all pregnant women. The following women are eligible for NT ultrasound as a component of Integrated Prenatal Screen (IPS = SIPS in combination with NT):
- Women ≥ 35 year old at expected date of delivery (EDD);
- Women with twin pregnancies;
- Women pregnant following in vitro fertilization with intracytoplasmic sperm injection (IVF with ICSI) and without preimplantation genetic testing.
In order to ensure the quality of NT ultrasound, every sonographer must annually perform a minimum number. As such, pregnant women 30 years and older from the Northern Health Authority and Kootenay Boundary Region are also eligible for an NT ultrasound as part of IPS (in order for sonographers to perform annually the minimum number of NT's required to maintain certification).
What accommodation has been made in the guidelines for communities with limited/no access to NT?
- There are many NT sites are operational in all of BC's health authorities. Eligible women able to travel may be accommodated at any NT site.
- The risk cut-off for SIPS has been adjusted to enable the same detection rate for Down syndrome in women 35 years and older as IPS (NT and serum integrated biochemistry). False positive rates will be higher for women who have not had an NT.
- Detection and false positive rates for SIPS and Quad screening meet the recommendations of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and the Canadian College of Medical Geneticists (CCMG).
What if a woman qualifies for an NT ultrasound measurement but cannot get it because there is no NT centre nearby that provides this service or the nearby centre is fully booked?
- If the woman is able to travel, she may be accommodated at any NT site in the province; OR
- Offer SIPS. This is a good alternative as it provides an equivalent high detection rate for Down syndrome and the only downside is that the false positive rate is higher than with the integrated prenatal screen (SIPS plus NT ultrasound).
- For women 40 or older with a singleton pregnancy or 35 or older with a multiple gestation pregnancy, amniocentesis should be offered as an option.
Why is IPS not offered to women younger than 35 years old as part of the BC Prenatal Genetic Screening Program?
- SIPS and Quad screens are available to women of all ages and are high quality screens that meet recommended national and international standards for prenatal screening.
- The capacity in BC for NT ultrasound measurement is limited (due to technological and medical expertise) and NT is reserved for women who would benefit most.
- The chance of a false positive result is higher for women 35 and older, thus, women in that age group can benefit most.
- NT is also offered where the woman or her partner has had a previous child or fetus with Down syndrome, trisomy 18 or trisomy 13 (trisomy 13 increases the risk of Down syndrome), women with multiple gestations, and women with a pregnancy conceived by IVF with ICSI.