Background: Preeclampsia is classified as early onset and late onset types with different clinical manifestation and pathogenesis. Placental pathology of preeclampsia has been largely based on description of the early onset type, and the morphologic features of placenta from late onset preeclampsia were similar to those of non-preeclamptic placentas. Objective: To identify clinically relevant maternal and neonatal risk characteristics and placental pathology for early onset and late onset preeclampsia. Study design We have collected all placental pathology information as well as maternal and neonatal birth information from March 2020 to December 2021 including preeclampsia and non-preeclampsia patients. We compared preterm and term preeclampsia in regards to maternal and neonatal complication and placental pathology by using logistic regression models to determine the important clinical risk factors associated with preeclampsia and placental pathology. Results A total 3724 placentas including 614 placentas from preeclamptic and 3110 non-preeclamptic patients were studied. Preterm preeclampsia (<37 weeks) was similar to early onset preeclampsia (<34 weeks) in maternal and neonatal complications as well as placental pathology, and these features were statistically different from those from term preeclampsia. More male fetuses were associated with early onset preeclampsia and female fetuses associated with late onset term preeclampsia when compared to non-preeclamptic patients. Maternal race/ethnicity and marital status were associated with preeclampsia but this association was no longer significant after logistic regression analysis. Preterm preeclampsia was statistically associated with gestational diabetes, placental infarcts, intrauterine fetal growth restriction and fetal vascular malperfusion, whereas term preeclampsia was associated with decidual vasculopathy and maternal obesity. Conclusions Early onset preeclampsia is a different clinical syndrome from the late onset type with clinical implication of pathogenesis and management.

The authors have declared no competing interest.

This study did not receive any funding.

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 study was approved by the Institutional Review Board (IRB) at New York Presbyterian Brooklyn Methodist Hospital, Brooklyn, NY ([1592673-1]).

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 and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

All data produced in the present work are contained in the manuscript.