The association between the use of fertility indicators and fecundability in a  Danish preconception cohort

Emma Skovgaard Pedersen; Ellen M Mikkelsen; Henrik Toft Sørensen; Elizabeth E Hatch; Lauren A Wise; Kenneth J Rothman; Joseph B Stanford; Anne Sofie Dam Laursen

doi:10.1111/ppe.13108

Fertility Awareness Effectiveness

The association between the use of fertility indicators and fecundability in a Danish preconception cohort

Pedersen ES, Mikkelsen EM, Sørensen HT, Hatch EE, Wise LA, Rothman KJ, Stanford JB, Laursen ASD

Published November 2024 Paediatric and Perinatal Epidemiology, 38(8), 641-650

DOI 10.1111/ppe.13108 PMID 39109606 PMC PMC11603762

RRM Academy Synopsis

Fertility indicators tied to higher pregnancy chances in Danish women

Fertility indicator use was linked to a 14% higher chance of pregnancy each cycle, a Danish web cohort of 11,328 women trying to conceive found. Cervical fluid checks had the largest link. Basal body temperature was not associated with a higher chance of pregnancy.

Key Findings

Cervical fluid monitoring had an adjusted fecundability ratio of 1.46 (95% CI 1.03, 2.07), urinary ovulation testing 1.35 (1.16, 1.58) and counting days 1.18 (1.09, 1.29).
The adjusted ratio for any indicator against none was 1.14 (95% CI 1.08, 1.19). Life table pregnancy estimates over 12 cycles were 86.3% for users and 82.5% for non-users.
Confidence intervals included 1.00 for feeling ovulation (1.15, 95% CI 0.88, 1.50), fertility apps (1.08, 0.96, 1.22) and basal body temperature (0.63, 0.28, 1.41).
With attempt time of two cycles or fewer and two cycles of follow-up, the adjusted ratio for any indicator was 1.21 (95% CI 1.13, 1.31).
At study entry, 63.3% of the 11,328 women used an indicator. Counting days was most common (46.9%) and basal body temperature least (3.0%).

Interpretation

This cohort study followed 11,328 Danish women aged 18 to 49 who had tried to conceive for six cycles or fewer, without fertility treatment. The main analysis used indicator use reported at study entry. A secondary analysis reassessed use every two cycles. The authors adjusted for age, income, health behaviors and reproductive history. Women who had tried longer were more likely to use an indicator, which the authors say likely underestimates the association. The findings support larger studies of fertility indicator use among couples trying to conceive.

RRM Context

Cervical fluid and urinary ovulation tests read signs from the current cycle. Counting days and some apps estimate from past cycles. Among women of normal fecundity, the day of ovulation varies widely, as the authors note. Cervical fluid observation is a central sign in cycle-charting-informed methods such as the Creighton Model FertilityCare System, which teach couples to read the current cycle.

Our editorial summary of this paper, not the article's abstract.

Abstract

Background

The use of fertility indicators to predict ovulation has largely been studied for contraceptive purposes, while less so as fertility-promoting tools.

Objective

To investigate the association between fertility indicators and fecundability in Danish women trying to conceive.

Methods

Web-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 (CI) using proportional probabilities regression models adjusted for age, socio-economic position, health indicators, reproductive history and gynaecological factors.

Results

Fertility 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).

Conclusion

In this Danish preconception cohort, use of fertility indicators was associated with a higher fecundability, varying by type of indicator.

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Fertility Awareness Methods Compared

Topics

Fertility Awareness › Effectiveness › Fertile Window Estimation · Menstrual Cycle › Cycle Biomarkers › Basal Body Temperature

Emma Skovgaard Pedersen, Ellen M Mikkelsen, Henrik Toft Sørensen, Elizabeth E Hatch, Lauren A Wise, Kenneth J Rothman, Joseph B Stanford, Anne Sofie Dam Laursen

E Pedersen, E Mikkelsen, H Sørensen, Liz Hatch, Beth Hatch, Betsy Hatch, E Hatch, L Wise, Ken Rothman, K Rothman, Joe Stanford, Joey Stanford, J Stanford, A Laursen

PMID 39109606 39109606 DOI 10.1111/ppe.13108 10.1111/ppe.13108 Pedersen et al. 2024, Pedersen 2024