Reliability of second trimester triple screening for Down syndrome in rhesus-negative women

To find out whether there is considerable influence on second trimester serum concentrations owing to the rhesus status.

This retrospective cohort study was performed at the Perinatology Unit of the GATA Haydarpasa Teaching Hospital. During the study interval, 2265 pregnancies met inclusion criteria. The blood samples were collected in 117 pregnancies with a maternal rhesus-negative blood group status. The control group consisted of 2148 pregnancies with a maternal rhesus-positive blood group status. Statistical analysis was performed by SPSS 11.0 statistical software.

Pregnancies with a maternal rhesus-negative blood group status were identified in 117 patients. The overall prevalence of pregnancies with a maternal rhesus-negative blood group status were 5.1% in our study. Only unconjugated estriol multiples of the median values were significantly decreased in rhesus-negative women (P<0.001). Alpha-fetoprotein and human chorionic gonadotrophin multiples of the median values did not differ significantly (P>0.05).

We conclude that if second trimester screening test to be used in Rh negative pregnancies, either the corrected value should be referred or double test result should be considered ignoring the unconjugated estriol result. Another option is the first trimester Down syndrome screening test.