Research Methods · Study Design
RRM Academy Synopsis
Chile cohort has sampled 292 cycles to study early pregnancy signals
A Chilean preconception cohort of healthy women trying to conceive, sampled day by day around ovulation, has fully documented and sampled 292 menstrual cycles so far. The paper is a preprint. The cycles include those of comparison women who were not trying to conceive. The paper reports no results on early pregnancy signals yet.
Key Findings
- Researchers contacted 1,183 women in Chile. 223 met all eligibility requirements, and 129 women trying to conceive finished at least one complete cycle of the protocol.
- 35 of those 129 women achieved full-term pregnancies.
- 40 abstinent women and 5 sterilized women, who were not trying to conceive, also completed the protocol as comparison groups.
- 49 of the 223 enrolled participants withdrew from the protocol (21.97%), for personal or medical reasons.
- Cervicovaginal fluid collection reached 3,956 of 4,380 expected samples (90.3%) from day 0 to 14. Blood collection reached 1,499 of 3,600 expected samples (41.6%) across seven scheduled collections.
Interpretation
The paper is a medRxiv preprint, so peer review has not certified it. It reports who enrolled and what was collected, and it tests no hypothesis. Eligibility rules included age 18 to 40, regular cycles and no chronic disease. The authors say selective recruitment in one region may limit how far findings apply. Blood was sampled less completely than other fluids. Samples came only from women, and medical histories were self-reported.
RRM Context
Ovulation timing sets which days count as the window around implantation, so the design depends on knowing when ovulation happened. The team identified ovulation with ultrasound, a fertility monitor, or LH strips. The cohort follows natural conception in women whose ovulation timing the study tracks, as cycle charting does in restorative reproductive medicine. Its results would describe healthy women. Women with a history of endometriosis were excluded.
Abstract
Background
Maternal-embryonic signalling involves intense and complex molecular exchange between the maternal reproductive system and the early embryo. This interaction begins after fertilisation but is poorly understood before implantation. EARLY-PREG is structured as a bidirectional prospective–retrospective preconception open cohort designed to characterise time-dependent molecular signatures of maternal–embryonic communication during the earliest stage of pregnancy. The cohort supports a dynamic and structured longitudinal biobank of maternal biological fluids, cells and tissues-derived samples collected during the peri-implantation window.
Study Design
Participants were recruited in three rolling waves from 2017 to 2024 so far, in Concepcion, Chile. Healthy women trying to conceive were enrolled and completed a survey with health, lifestyle, and sociodemographic data. Menstrual cycles were prospectively monitored with ovulation and fertile window ascertainment (ultrasound, fertility monitor, and/or LH strips) and followed for a maximum of six consecutive cycles or until implantation of a viable embryo exposure occurred. Each cycle was synchronised within a longitudinal repeated-measures design incorporating systematic day-by-day sampling anchored to ovulation (day 0). Biological samples include cervicovaginal fluid (CVF), urine, saliva, and blood. In addition, cervical brushings were collected during the peri-implantation window (days 12–14 post-ovulation) and on day 21 post-ovulation. Retrospective temporal alignment of ovulation and defined physiological windows was performed using hormonal curves (LH, oestradiol, progesterone and beta-hCG) measured in stored blood and urine samples.
Results to Date
At present, 1,183 women have been contacted, of whom 223 met all eligibility criteria. Among participants trying to conceive, 129 completed at least one full longitudinal repeated-measures cycle; 35 achieved full-term pregnancies and 17 experienced early pregnancy loss (ELP). In addition, 40 abstinent and 5 sterilised women completed the protocol. To date, 292 menstrual cycles have been fully documented and sampled. 52 cycles correspond to conception cycles and 240 cycles to the absence of embryo implantation. Among the latter, 31 cycles were classified as non-conception counterfactual cycles and 209 to non-counterfactual cycles. The biorepository encompasses maternal biological samples collected during the first 2 weeks after ovulation across all documented cycles. Biospecimen collection compliance exceeded predefined protocol thresholds for most sample types.
Current and Future Directions
The cohort currently supports longitudinal proteomic analyses within a within-individual counterfactual framework, comparing the exposure to a viable embryo implantation (conception cycle) with the absence of embryo implantation (non-conception cycle) to characterise time-dependent molecular signatures of early pregnancy. Additional outcomes of the cohort include implantation failure and early pregnancy loss. A fourth rolling recruitment wave is planned for 2026 to characterise time-dependent immunophenotypic variation in maternal peripheral blood mononuclear cells (PBMCs) during early pregnancy stages.
Study Funding
This work forms part of the EARLY-PREG preconception open cohort and has been supported by research grants awarded by Fundación de Investigación San Ramón (FISAR), Chile. The pilot study and first recruitment wave were supported by grants #MEL109112011 and #MEL109112011R4 awarded to E.S.K., C.V., and J.F.S. The second recruitment wave was supported by grants #MEL109112011R5 and #MEL131032017R1 awarded to E.S.K. The third wave was supported by grant #MEL205062018 awarded to E.S.K. and M.H. Current funding for the fourth recruitment wave and mass spectrometry research on maternal CVF is supported by grant REH042024-01 awarded to M.H., G.N., and E.S.K.
Trial Registration
NCT07358026.