Since most women who have screening (of any type) will have a screen negative result, getting the results earlier may mean earlier peace of mind.
Regardless of the screening test chosen, all women with a screen positive result will be offered a diagnostic test to find out for sure whether the pregnancy is affected. This is a very important step before making a decision about the pregnancy. When NIPT is used as a first screen in women of all ages, a positive NIPT test result indicating a risk of Down syndrome greater than 99% can still be a false positive result. In fact, if 10 young women having NIPT as their only screen have a positive NIPT result with a risk of Down syndrome greater than 99%, only 6-8 of them will have a baby with Down syndrome. The other women have healthy babies and their test result was actually a false positive.
Women who screen positive by NIPT should be offered genetic counselling to discuss their options for diagnostic testing. One option is chorionic villi sampling (CVS), which occurs between 11 and 13 weeks) and is only available at BC Women’s Hospital & Health Centre. The other option is an amniocentesis, which can be done as early as 14 weeks in women at very high risk of a chromosomal abnormality. The amniocentesis is considered the option of choice given the cells tested come from the fetus. However, factors such as gestational age at the time of the positive result, ultrasound findings, chromosome involved, and maternal age must be considered when deciding which procedure to have.
Women who screen positive by IPS or SIPS would be offered an amniocentesis, which normally occurs anytime after 15 weeks. Amniocentesis is available at many hospitals around the province.
Both CVS and amniocentesis are covered by MSP for women who screen positive. Results from either a CVS or amniocentesis will tell whether the baby has a chromosome abnormality such as Down syndrome. For women having an amniocentesis because of an increased risk of Down syndrome or trisomy 18, if a rapid lab test is done, results are available in three days. If an analysis of all chromosomes is done, results take about two weeks. If the pregnancy is found to carry a chromosome abnormality, a woman has the option to continue or end the pregnancy.