Prenatal diagnosis versus first-trimester screening of trisomy 21 among pregnant women aged 35 or more.

OBJECTIVE

To compare the policy of prenatal diagnosis versus first trimester screening of trisomy 21 among pregnant women of advanced age.

METHODS

A retrospective study was conducted on patients aged ≥35 divided in two groups: patients who requested first trimester combined test and only in case of screen-positive result underwent invasive testing (group A); patients undergoing chorionic villous sampling or amniocentesis as first investigation (group B). The following outcome variables were compared: antenatal detection of trisomy 21, occurrence of trisomy 21 at birth, miscarriage rate, hospitals' costs.

RESULTS

4527 women were included. Of these, 534 (11.80%) underwent T21 screening whereas 3993 (88.20%) requested primary invasive testing. In group A, 64 combined test were positive (11.99%) and 8 trisomy 21 cases were diagnosed (1.50%); the loss of euploid fetuses after invasive procedure was 4.55% (2/44). No false-negative case was observed. In group B 57 cases of trisomy 21 were diagnosed (1.43%), and pregnancy loss rate of chromosomally normal fetuses was 0.45% (17/3806). The estimated cost was, respectively, 67.720€ for the primary screening versus 1.996.500€ for direct prenatal diagnosis.

CONCLUSION

First trimester screening of trisomy 21 is highly accurate and cost saving among women ≥35.