A microphysiological model of human trophoblast invasion during implantation.

Successful establishment of pregnancy requires adhesion of an embryo to the endometrium and subsequent invasion into the maternal tissue. Abnormalities in this critical process of implantation and placentation lead to many pregnancy complications. Here we present a microenigneered system to model a complex sequence of orchestrated multicellular events that plays an essential role in early pregnancy. Our implantation-on-a-chip is capable of reconstructing the three-dimensional structural organization of the maternal-fetal interface to model the invasion of specialized fetal extravillous trophoblasts into the maternal uterus. Using primary human cells isolated from clinical specimens, we demonstrate in vivo-like directional migration of extravillous trophoblasts towards a microengineered maternal vessel and their interactions with the endothelium necessary for vascular remodeling. Through parametric variation of the cellular microenvironment and proteomic analysis of microengineered tissues, we show the important role of decidualized stromal cells as a regulator of extravillous trophoblast migration. Furthermore, our study reveals previously unknown effects of pre-implantation maternal immune cells on extravillous trophoblast invasion. This work represents a significant advance in our ability to model early human pregnancy, and may enable the development of advanced in vitro platforms for basic and clinical research of human reproduction.

Uterine natural killer cell biology and role in early pregnancy establishment and outcomes.

Objective: While immune cells were originally thought to only play a role in maternal tolerance of the semiallogenic fetus, an active role in pregnancy establishment is becoming increasingly apparent. Uterine natural killer (uNK) cells are of specific interest because of their cyclic increase in number during the window of implantation. As a distinct entity from their peripheral blood counterparts, understanding the biology and function of uNK cells will provide the framework for understanding their role in early pregnancy establishment and adverse pregnancy outcomes. Evidence Review: This review discusses unique uNK cell characteristics and presents clinical implications resulting from their dysfunction. We also systematically present existing knowledge about uNK cell function in three processes critical for successful human embryo implantation and placentation: stromal cell decidualization, spiral artery remodeling, and extravillous trophoblast invasion. Finally, we review the features of uNK cells that could help guide future investigations. Results: It is clear the uNK cells are intimately involved in multiple facets of early pregnancy. This is accomplished directly, through the secretion of factors that regulate stromal cells and trophoblast function; and indirectly, via interaction with other maternal cell types present at the maternal-fetal interface. Current work also suggests that uNK cells are a heterogenous population, with subsets that potentially accomplish different functions. Conclusion: Establishment of pregnancy through successful embryo implantation and placentation requires crosstalk between multiple maternal cell types and invading fetal trophoblast cells. Defects in this process have been associated with multiple adverse perinatal outcomes including hypertensive disorders of pregnancy, placenta accreta, and recurrent miscarriage though the mechanism underlying development of these defects remain unclear. Abnormalities in NK cell number and function which would disrupt physiological maternal-fetal crosstalk, could play a critical role in abnormal implantation and placentation. It is therefore imperative to dissect the unique physiological role of uNK cells in pregnancy and use this knowledge to inform clinical practice by determining how uNK cell dysfunction could lead to reproductive failure.

Trends and correlates of monozygotic twinning after single embryo transfer.

OBJECTIVE: To evaluate trends of monozygotic twinning after single embryo transfer and its association with patient and treatment factors. METHODS: Our retrospective cohort study included 28,596 pregnancies after fresh, nondonor single embryo transfer during 2003-2012 reported to the National ART Surveillance System. We examined trends of monozygotic twin pregnancies (number of fetal heart tones on first-trimester ultrasonography more than one or number of neonates born more than one) and assessed patient and treatment factors for monozygotic twin compared with singleton pregnancies. Modified Poisson regression models were used to estimate adjusted risk ratios (RRs) and 95% confidence intervals (CIs) for association between monozygotic twinning and selected factors stratified by day 2-3 and day 5-6 transfer. RESULTS: During 2003-2012, the incidence of monozygotic twinning after single embryo transfer was lower for day 2-3 transfers than for day 5-6 transfers (1.71%, 95% CI 1.45-1.98, n=162 compared with 2.50%, 95% CI 2.28-2.73, n=472); the incidence did not change significantly over the study period. Among day 2-3 transfers, assisted hatching increased the risk for monozygotic twinning compared with singletons (adjusted RR 2.16, 95% CI 1.53-3.06); use of intracytoplasmic sperm injection decreased the risk (adjusted RR 0.60, 95% CI 0.42-0.85). Having one or more prior pregnancies increased the risk for monozygotic twinning among day 5-6 transfers (adjusted RR 1.26, 95% CI 1.03-1.53). CONCLUSION: Monozygotic twinning after single embryo transfers was more common among day 5-6 embryo transfers than day 2-3 transfers. Use of assisted hatching was associated with increased risk for monozygotic twinning for day 2-3 transfers. LEVEL OF EVIDENCE: II.

Numerical and experimental investigation of pulsatile hemodynamics in the total cavopulmonary connection.

Computational fluid dynamics (CFD) tools have been extensively applied to study the hemodynamics in the total cavopulmonary connection (TCPC) in patients with only a single functioning ventricle. Without the contraction of a sub-pulmonary ventricle, pulsatility of flow through this connection is low and variable across patients, which is usually neglected in most numerical modeling studies. Recent studies suggest that such pulsatility can be non-negligible and can be important in hemodynamic predictions. The goal of this work is to compare the results of an in-house numerical methodology for simulating pulsatile TCPC flow with experimental results. Digital particle image velocimetry (DPIV) was acquired on TCPC in vitro models to evaluate the capability of the CFD tool in predicting pulsatile TCPC flow fields. In vitro hemodynamic measurements were used to compare the numerical prediction of power loss across the connection. The results demonstrated the complexity of the pulsatile TCPC flow fields and the validity of the numerical approach in simulating pulsatile TCPC flow dynamics in both idealized and complex patient specific models.