O-290 Reduced uterine artery pulsatility index (UtAPI) in artificial frozen embryo transfer pregnancies leads to underestimation of 1st-trimester preeclampsia risk. An analysis of over 30,000 pregnancies
Authors: Polyzos N  P , Donno V , Rodríguez Garcia I 
Published: July 2024

Abstract

Study question
Does the mode of conception (spontaneous, ovulation induction, fresh or frozen embryo transfer) impact Uterine Artery Pulsatility Index (UtAPI) values in 1st-trimester preeclampsia screening?

Summary answer
A significant reduction in UtAPI during 1st-trimester screening is observed in artificial frozen embryo transfer (AC-FET) pregnancies, resulting in underestimated preeclampsia risk.

What is known already
Accumulating evidence indicates that AC-FET cycles are associated with an increased risk of preeclampsia.
Uterine artery (UtA) Doppler is a crucial biomarker for first-trimester preeclampsia screening, along with maternal factors and serum biomarkers, identifying “high-risk” patients. Guidelines strongly recommend the administration of aspirin(150mg/day) in these women, owing to robust evidence demonstrating a 40% reduction in the incidence of preeclampsia.
Despite small studies suggesting a lower UtAPI after frozen ET, no previous studies explored the impact of the type of endometrial preparation in UtAPI Doppler or its influence on estimating preeclampsia risk

Study design, size, duration
This is a retrospective single-center study including 33880 singleton pregnancies (spontaneous or after ART) who underwent the 1st-trimester ultrasound screening at our University Hospital between January 2010 - May 2023. Overall, 33880 pregnancies were included: 29709 spontaneous, 429 ovulation induction, 1015 fresh ET and 2727 after frozen ET pregnancies (326/2727 in NC-FET and 2401 in AC-FET).

Participants/materials, setting, methods
The study included only singleton pregnancy for which a first trimester ultrasound (11+0- 13+6 wks) with UtA Doppler was performed. The primary aim of the study was to assess whether there was an association between the mode of conception and the UtA Doppler and whether UtAPI differed according to the type the endometrial preparation for FET. Continuous variables were expressed as mean ± SD. ANOVA test and multivariate regression analysis were performed.

Main results and the role of chance
Overall, the 1st-trimester UtAPI in pregnancies conceived after AC-FET was 1,036±0,160 [CI95%:0,723;1,349], after NC-FET 1,354±0,162 [CI95%:1,037;1,671], Fresh-ET 1,418 ±0,161 [CI95%:1,104;1,733], OI 1,413±0,162 [CI95%:1,096;1,730] and spontaneous pregnancies 1,373 ± 0,160 [CI95%:1,060;1,686].
A multivariable regression analysis, adjusting for confounding factors (age, weight, smoking, and oocyte donation), demonstrated that the value of uterine artery UtAPI is significantly lower when artificial cycle for frozen embryo transfer is performed compared with spontaneous pregnancies (-0,337 ± 0,014 [CI95%:-0,378;-0,297]), ovulation induction (-0,377 ± 0,028 [CI95%:-0,455; -0,298]) Fresh-ET (-0,383 ±0,021 [CI95%:-0,442; -0,323]), and NC-FET (-0,318 ± 0,029[CI95%:-0,401; -0,23]). On the contrary none of the other modes of conception are different in terms of UtAPI as compared with spontaneous pregnancies.
Among screened patients, the number of patients classified at high risk for preeclampsia was significantly lower in pregnancies following AC-FET 7.8%(156/2002) as compared to NC-FET 15.9%(46/289), fresh-ET 11.0%(58/527), ovulation induction 10.5%(26/248) and spontaneous pregnancies (1452/15624) p &lt; 0.001. Nonetheless, despite the lower number of high-risk patients in the AC-FET group, the actual incidence of PE was more than three times higher in AC-FET group 5.2%(125/2401) as compared with spontaneous 1.5%(431/29709), ovulation induction 1.4%(6/429) or NC-FET pregnancies 1.5%(5/326) and more than two times higher when compared to fresh-ET pregnancies 2.3%(23/1015) p &lt; 0.001.

Limitations, reasons for caution
Despite employing a robust methodology with a substantial sample size and multivariate statistical analysis to address confounding factors, it’s essential to acknowledge the possibility of residual bias. However, its impact on the presented outcomes is anticipated to be minimal.

Wider implications of the findings
Existing 1st-trimester preeclampsia screening calculators overlook the notably lower UtAPI in AC-FET pregnancies, as discovered in our study. This poses a threat of underestimating high-risk patients and neglecting prophylactic aspirin. Algorithms should be adjusted to accurately assess risk for those undergoing AC-FET

Trial registration number
Not applicable