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Article History

Received: 14 May 2021

Accepted: 29 November 2021

First Online: 27 January 2022

Declarations

:

: The collection of 2nd and 3rd trimester placental tissues was approved by the Ethics Committee of the Johann Wolfgang Goethe University Hospital Frankfurt (reference number: 375/11). The six formalin-fixed and paraffin-embedded 1st trimester placental tissue sections were kindly provided by Dr. Qi Chen, University of Auckland, New Zealand, and Fudan University, Shanghai, China. The collection of these samples was approved by the Ethics Committee of the Hospital of Obstetrics and Gynecology of Fudan University, China (reference number: 2018-62). The sampling of 1st trimester placentas at the Medical Practice for Gynecology and Obstetrics led by Dr. Thorsten Nowak was approved by the Ethics Committee of the Johann Wolfgang Goethe University Hospital Frankfurt (reference number: 19-455). The umbilical vein sample collection was approved by the Ethics Committee of the Johann Wolfgang Goethe-University Hospital Frankfurt (reference number: 19-201). Informed written consents were obtained from all donors.

: Not applicable.

: The authors declare that they have no competing interests.