# 3/3- A randomized controlled trial of frozen embryo transfers performed in modified natural versus programmed cycles (NatPro)

> **NIH NIH R01** · STANFORD UNIVERSITY · 2021 · $308,501

## Abstract

PROJECT SUMMARY
 Of the estimated 1.6 million cycles of assisted reproductive technology (ART) performed globally in one
year, nearly one third are categorized as frozen embryo transfer (FET). In the United States, over half of the ART
cycles involve FET or freezing of all embryos. Given this widespread use of FET, it is of serious concern that
multiple studies have demonstrated an association of FET with an increased risk for hypertensive disorders of
pregnancy, including preeclampsia. It is critical that this risk be minimized because preeclampsia is associated
with severe short- and long-term consequences for both mother and infant, including maternal mortality and fetal
death. Furthermore, several recent meta-analyses emphasized that the evidence to guide clinicians about
protocol choice for optimizing live birth rate with FET is poor.
 Our group has recently completed an NIH-sponsored Program Project Grant, with findings that strongly
implicate one commonly performed FET protocol as an explanation for the increased risk of preeclampsia seen
with FET. In a prospective cohort study, one protocol (the programmed FET) was associated with significantly
higher rates of preeclampsia compared with an alternative protocol (the natural cycle FET). Furthermore,
through detailed examination of maternal cardiovascular adaptation to pregnancy in two separate populations,
perturbations of concern were seen with programmed FET, but not with natural cycle FET.
 Given these data and other findings in the literature, our central hypothesis is that pregnancy resulting
from an FET in a natural cycle will have a lower rate of preeclampsia compared to an FET in a programmed
cycle. To test this hypothesis, we will conduct a randomized, clinical trial at 6 sites. Our Primary Specific Aim
is to determine the incidence of preeclampsia with the natural versus the programmed cycle. Our second
hypothesis is that the live birth rate following transfer in a natural cycle is similar to that in a programmed FET,
to be tested through a Second Specific Aim in which we compare the live birth rate with the natural versus the
programmed cycle. All embryos will have been created prior to enrollment in the trial and no embryo will be
subjected to increased risk in the course of this research.
 With successful completion of this protocol, we will have established the live birth rates for natural cycle
FET compared to a programmed FET cycle, utilizing contemporary standardized protocols. If the natural cycle
is confirmed to be associated with a lower risk of preeclampsia, this study will enhance the safety of ART for
millions of women who are undergoing FET worldwide. This research proposal is highly responsive to the RFA
and the overall mission of NICHD and NIH, as it will not only compare the live birth rates associated with two
commonly used contemporary FET protocols, but it will perhaps even more importantly, compare the safety of
these FET protocols with respect to maternal hea...

## Key facts

- **NIH application ID:** 10247787
- **Project number:** 5R01HD100334-03
- **Recipient organization:** STANFORD UNIVERSITY
- **Principal Investigator:** Ruth B Lathi
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $308,501
- **Award type:** 5
- **Project period:** 2019-09-26 → 2024-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10247787

## Citation

> US National Institutes of Health, RePORTER application 10247787, 3/3- A randomized controlled trial of frozen embryo transfers performed in modified natural versus programmed cycles (NatPro) (5R01HD100334-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10247787. Licensed CC0.

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