RESEARCH QUESTION: What is the association between the development of pre-eclampsia and endometrial preparation prior to vitrified-warmed embryo transfer (frozen embryo transfer, FET)?
DESIGN: A retrospective cohort study at a tertiary university-based hospital, including a total of 536 pregnant patients who underwent a FET between 2010 and 2019 and delivered in the same institution; 325 patients underwent natural cycle FET (NC-FET) and 211 artificial cycle FET (AC-FET).
RESULTS: Unadjusted, the incidence of pre-eclampsia was significantly higher in AC-FET cycles than in NC-FET cycles (3.7% versus 11.8%, P < 0.001). Multivariable logistic regression analysis showed that, when adjusting for type of endometrial preparation (artificial cycle versus natural cycle), oocyte recipient cycles and African ethnicity, the risk of developing pre-eclampsia was significantly associated with artificial endometrial preparation or oocyte recipient cycles (AC-FET versus NC-FET: odds ratio 2.9, 95% confidence interval 1.4-6.0, P = 0.005).
CONCLUSIONS: The current data show a higher incidence of pre-eclampsia in AC-FET versus NC-FET cycles, adding further strength to the existing data on this topic. Together, these recent findings may result in a change in clinical practice, towards a preference for NC-FET cycles over AC-FET cycles in ovulatory patients. Screening for high-risk patients and the development of strategies to mitigate their risk profile could reduce the risk of pre-eclampsia. Further understanding of the different vasoactive substances excreted by the corpus luteum is vital.