First Trimester Combined Screening in Hong Kong, China: outcome first 10000 cases

Objective: To examine the effectiveness of first trimester fetal Trisomy 21 (T21) screening using a combination of maternal age, nuchal translucency (NT), maternal serum fb-hCG and PAPP-A and levels in a predominantly Chinese population in Hong Kong.

Methods: It was a prospective study performed in a University Fetal Medicine Unit between June 2003 and February 2007. Consecutive women who underwent the combined screning for T21 between 11 and 13+6 weeks of gestation were recruited. NT was measured according to the criteria set by Fetal Medicine Foundation (FMF). Maternal serum fb-hCG and PAPP-A levels was measured by Kryptor analyser. Risk of T21 was calculated using FMF's algorithm. Fetal karyotyping was advised when the risk was 1: 300 or above. All subjects were followed up for pregnancy and fetal outcome.

Results: Among the 10185 women underwent the screening programme, 99% were Chinese and 178 women had a twin pregnancy, adding up 10363 fetuses in total. 27.4% of the women were at or above 35 years old. 618 fetuses were screened positive (5.9%), which included 31 cases of T21, 14 cases of T18, 7 cases of T13, 10 cases of 45XO, and 7 cases of other chromosomal abnormalities. The overall positive predictive value was 1 in 9. Among the 9745 screened negative fetuses, only 50 cases had an unknown fetal outcome. 3 cases of T21 and 4 cases of other chromosomal abnormalities were screened negative, but all except one T21 were picked up during second trimester morphology scan. The detection rate for T21 with first trimester screening was 91.2% (31 / 34).

Conclusion: First trimester combined screening for fetal T21 is highly effective among Chinese subjects in Hong Kong.