Background The aim of the study was to investigate the combination of cell-free fetal hemoglobin (cfHbF), total cell-free hemoglobin (tcfHb), cell-free fetal DNA (cffDNA), Pregnancy Associated Plasma Protein A (PAPP-A) and maternal obstetric history as potential markers in first and second trimester, for prediction of preeclampsia (PE) in asymptomatic pregnant women.

Methods This was a retrospective case-control study of 589 pregnant women (560 in the control group and 29 with PE in the case group). We used routine blood samples used in screening for chromosomal anomalies and rhesus immunization to analyze the levels of cfHbF, tcfHb, and PAPP-A in gestational weeks 8–14 and levels of cfHbF, tcfHb, and cffDNA in gestational weeks 23–28.

Results In first-trimester samples, there was no statistically significant difference between controls, mild PE, and severe PE regarding levels of PAPP-A, cfHbF, tcfHb or cfHbF/tcfHb ratio. In second-trimester samples, cfHbF and cffDNA levels were significantly higher in PE cases than in controls. The odds ratio (OR) for developing PE was 4.28 (95%CI: 1.85–9.89) given a cfHbF>90th centile (p<0.001), and 6.55 (95%CI: 2.61–16.46) given a cffDNA level>90th centile (p<0.001). When adjusting for BMI and previous history of PE in a logistic regression analysis, only cffDNA and BMI remained statistically significant (p< 0.001).

Conclusion We found a significant association between PE and high levels of cfHbF and cffDNA in second-trimester samples, but no statistically significant difference in first-trimester samples were observed.

The authors have declared no competing interest.

This project was part of a PhD scholarship and funding was received from Rigshospitalet, Copenhagen University Hospital, The Aase and Einar Danielsen Foundation, the Lundbeck Foundation and Arvid Nilssons Foundation.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Danish Research Ethics Committee gave ethical approval for this work (ref. H-3-2012-040).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

Data is available on reasonable request.