Affiliation:
1. Department of Clinical Epidemiology, Aarhus University Hospital Aarhus University Aarhus N Denmark
2. Boston University School of Public Health Boston Massachusetts USA
3. Division of Public Health, Department of Family and Preventive Medicine University of Utah Spencer Fox Eccles School of Medicine Salt Lake City Utah USA
Abstract
AbstractBackgroundThe use of fertility indicators to predict ovulation has largely been studied for contraceptive purposes, while less so as fertility‐promoting tools.ObjectiveTo investigate the association between fertility indicators and fecundability in Danish women trying to conceive.MethodsWeb‐based preconception cohort study. We analysed data from 11,328 females aged 18–49 years trying to conceive without fertility treatment for ≤6 menstrual cycles, from the Danish SnartGravid.dk and SnartForældre.dk cohorts (2007–2023). Participants reported the use of fertility indicators (counting days since the last menstrual period, cervical fluid monitoring, urinary ovulation testing, feeling ovulation, using a smartphone fertility app and measuring basal body temperature [BBT]). Time to pregnancy was measured in menstrual cycles ascertained by self‐reported pregnancy status. We estimated fecundability ratios (FR) and 95% confidence intervals (CIs) using proportional probabilities regression models adjusted for age, socio‐economic position, health indicators, reproductive history and gynaecological factors.ResultsFertility indicators were used by 63.3% of participants at study entry. Counting days was the most common (46.9%), while measuring BBT was the least (3.0%). Other indicators ranged from 17.0% to 23.6%, with 69.7% using more than one indicator. Compared with non‐use, use of any fertility indicator was associated with greater fecundability (adjusted FR 1.14, 95% CI 1.08, 1.19). Cervical fluid monitoring showed the strongest association (aFR 1.46, 95% CI 1.03, 2.07), followed by urinary ovulation testing (aFR 1.35, 95% CI 1.16, 1.58) and counting days (aFR 1.18, 95% CI 1.09, 1.29). Feeling ovulation and fertility apps were modestly associated with fecundability, while measuring BBT was not associated. Sensitivity analysis restricting to ≤2 cycles of attempt time and two cycles of follow‐up showed an aFR for any indicator use of 1.21 (95% CI 1.13, 1.31).ConclusionIn this Danish preconception cohort, use of fertility indicators was associated with a higher fecundability, varying by type of indicator.