Objective To investigate the effects of chorionicity in uncomplicated twin pregnancies on maternal circulating cell-free messenger RNA(cf-mRNA) and the effects of severe TTTS.

Methods A prospective cohort of MC twins complicated by severe TTTS (n=23) were studied, between October 2006 and December 2007. A cohort of uncomplicated DC (n=10) and MC (n=7) pregnancies were studied for comparison. Maternal cf-mRNA encoding GAPDH, sVEGFR-1, VEGF-A, Endoglin, PlGF, Tie-1, Ang-1 and Ang-2 were measured by a quantitative 1-step real-time PCR assay after extraction from maternal plasma(stored at −80°C).

Results The overall survival of this TTTS cohort was 69.6% livebirths (32/46) with ≤one survivor in 87% (20/23). The amounts of cf-mRNA detectable are reported for uncomplicated DC, MC and TTTS pregnancies respectively: GAPDH–80%,100% and 96%; sVEGFR-1–10%,0% and 26%; VEGF-A- 80%,71% and 96%; Endoglin–70%,71% and 91%; PlGF–70%,57%, 26%; Tie-1 0%,43%, 0%; Ang–1 71%,50% and 60% and Ang–2 83%,50% and 89%. There was a significant difference in VEGF-A(medians DC−337.3, MC–390.8, TTTS–618.6 copies/ml plasma p=0.024), Endoglin(medians DC-14.49, MC-1171, TTTS–2896 copies/ml plasma p=0.027) and Ang-2(medians DC-13.66, MC-8.49, TTTS 44.80 copies/ml plasma p=0.007).

Conclusion Maternal cf-mRNA could be reliably detected for GAPDH, PlGF, VEGF-A, Endoglin, Ang-1 and Ang-2 in twin pregnancies and significant difference demonstrated in VEGF-A, Endoglin and Ang-2 between uncomplicated twins and MC twin pregnancies complicated by TTTS. If such alterations in maternal cf-mRNA precede the onset of clinically apparent disease, this may be used as an adjuvant blood test to complement first trimester ultrasound screening.