Introduction: Fetal Growth Restriction (FGR) affects 5–10% of all pregnancies and is the leading cause of perinatal mortality [1]. FGR is typically defined as an estimated fetal weight in utero below the 10th percentile for a given gestational age and is associated with insufficient exchange of oxygen and nutrients. The transport of oxygen and nutrients occurs through the vasculature of the placenta, particularly in the microvasculature of the villous tissue [2]. The efficiency of this exchange is influenced by the architecture of the villous tissue, including factors such as the porosity and vascular branching. Since the placenta is fetal tissue, placental efficiency can depend on fetal sex [3]. While existing literature reports alterations in villous architecture with FGR [4], how the villous structure changes with fetal sex remains largely underexplored. Furthermore, male fetuses are 20% more likely to experience adverse outcomes in complicated pregnancies than female fetuses, highlighting the impact of fetal sex [3]. Understanding sex-based differences in the placenta villous tissue structure may elucidate reasons for sex differences in fetal outcomes. Therefore, the objective of this study was to determine the extent that fetal sex influences the villous structure of the placenta in low-risk and FGR pregnancies.
Materials and
Methods: Patient Recruitment: Patients were recruited under an IRB approved protocol. After birth, the fetal weight was recorded, and placenta villous biopsies were collected from a total of 32 patients, 16 of whom were diagnosed with FGR. Within the FGR case group, six pregnancies had a male fetal sex and ten pregnancies had a female fetal sex. Control patients with low-risk pregnancies were matched to the FGR patients according to fetal sex and total gestation time. Optical Clearing & Imaging: Placenta villous biopsies collected from each patient were optically cleared with Visikol Histo-1 [5]. Using optical coherence tomography (OCT), a minimum of 10 3D images of each placenta biopsy were acquired (cubes 2 mm on a side). 3D Villi Structure Analysis: OCT images were segmented, and the volume was reconstructed to calculate the average radius of the intervillous pore size (a) and the number of branches per volume (B) of the villous structure using an adapted MATLAB code previously developed to analyze porous structures [6]. Statistics: A linear mixed effect model with a type II sum of squares ANOVA was used, and p-values were adjusted for multiple comparisons using the Tukey method.
Results, Conclusions, and Discussions: Out of the total recruited patients with FGR in this study, only six neonates were male and ten neonates were female. As expected, male and female infants of FGR patients had lower birthweights compared to control patients. Consistent with results previously reported in the literature, female birthweights were less than male birthweights for both cases and controls, though this difference was not significant [3] (Fig. 1A). With OCT, the 3D architecture of the placenta villous tissue was imaged, segmented, and 3D reconstructed (Fig. 1B,C) to determine the extent that changes in the villous porosity and vascular branching were influenced by fetal sex (Fig. 1D). While the pore size (a) of the villous tissue in placentas from male fetuses was larger with FGR cases than controls, the pore size did not significantly change in placentas of female fetuses in cases and controls (Fig. 1E). Additionally, the quantified number of branches per cubic millimeter (B) was significantly greater in control pregnancies than FGR pregnancies for both female and male fetuses (Fig.1E). The decreased branching and larger intervillous space with FGR pregnancies is consistent will previous studies [4]. However, our results demonstrate that the change in pore size is greater for male fetuses, suggesting there may be sex differences that result in a change in oxygen and nutrient transport. This observation may help explain why fetal outcomes are typically worse for male fetuses with pregnancy complications [3]. Future work will develop computational models of oxygen transport in the villous structures to understand how these sex-dependent architecture changes lead to changes in placenta function. Overall, understanding how fetal outcomes are influenced by sex differences will help to better predict and prevent pregnancy complications.
Acknowledgements (Optional): Work on this project is supported by Wellcome Leap as part of the In Utero Program and the NIH T32 Postdoctoral Training Grant in Regenerative Medicine (T32EB028092).
