Abstract Body (Do not enter title and authors here): Introduction:
Assisted reproductive technologies have become increasingly common and have been associated with a higher risk of preeclampsia. Data suggests that programmed (medicated) protocols for frozen embryo transfer (FET), which suppress the formation of the corpus luteum, may impair cardiovascular adaptations and result in subsequent maternal placental syndromes.

Aims:
This study aims to understand the impact of absence of a corpus luteum during FET on the risk of preeclampsia and other adverse pregnancy outcomes.

Methods:
A retrospective chart review was conducted for patients who became pregnant utilizing in vitro fertilization from January 2019 through December 2024. Patients were included if they underwent FET and had a subsequent live birth at a single large academic medical center. Pregnancy and delivery outcomes were compared between patients who underwent a natural FET (with presence of corpus luteum) versus programmed/medicated protocol (with absence of corpus luteum). Clinical characteristics, outcomes, and management were compared between groups using the chi-square test.

Results:
A total of 994 patients were included: 751 in the natural FET group and 243 in the programmed FET group. The groups were similar in age (mean 37 years), race, and ethnicity. The programmed group had a statistically significantly higher obstetric comorbidity index (median difference p=0.022), indicating a slightly greater baseline burden of chronic illness. Median BMI was also higher in the programmed group (31 [IQR 28, 36] vs. 30 [IQR 27, 34], p = 0.013). Gestational hypertension or preeclampsia occurred more often in the programmed FET group than in the natural FET group, though this did not reach statistical significance (24% vs 19%, p = 0.12). The rate of preeclampsia with severe features was similar between groups (12% vs. 10% for programmed and natural groups, respectively). The use of inpatient antihypertensives (single or multiple agents), discharge on antihypertensives, and aspirin prophylaxis did not differ between groups.

Conclusion:
While hypertensive disorders in pregnancy appear numerically higher in the programmed FET group, none of the differences between the groups reached statistical significance. BMI and comorbidity scores, which could influence pregnancy outcomes, may need to be considered in risk stratification and counseling. The questions addressed in the study warrant further investigation.