Multilevel model to assess sources of variation in follicular growth close to the time of ovulation in women with normal fertility: a multicenter observational study
Mikolajczyk, R. T., Stanford, J. B., & Ecochard, R. (2008). Multilevel model to assess sources of variation in follicular growth close to the time of ovulation in women with normal fertility: a multicenter observational study. Reproductive Biology and Endocrinology : RB&E, 6(1), 61. https://doi.org/10.1186/1477-7827-6-61
Mikolajczyk RT, Stanford JB, Ecochard R. Multilevel model to assess sources of variation in follicular growth close to the time of ovulation in women with normal fertility: a multicenter observational study. Reprod Biol Endocrinol. 2008;6(1):61. doi:10.1186/1477-7827-6-61
Mikolajczyk, Rafael T., et al. "Multilevel model to assess sources of variation in follicular growth close to the time of ovulation in women with normal fertility: a multicenter observational study." Reproductive Biology and Endocrinology : RB&E, vol. 6, no. 1, 2008, pp. 61.
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Follicle size varies by cycle in women with normal fertility
Researchers scanned the ovaries of 107 women with normal fertility at eight European centers. Follicles grew at about the same speed across these women. Follicle size before ovulation changed from one cycle to the next in the same women. About 4 out of 10 cycles had a follicle under 19 mm the day before ovulation.
Key Findings
The analysis used 533 ultrasound measurements from 282 cycles in 107 women with normal fertility, recruited at 8 centers in 4 European countries.
Analysis showed no evidence for a center effect on growth rate or maximum follicular diameter. Growth rate was homogeneous across women and across cycles.
Maximum follicular diameter varied significantly between cycles, with no indication of differences between women. The mean was 20.48 mm, with a standard deviation of 3.98.
About 40% of cycles showed a follicle under 19 mm on the day before ovulation, in the observed data.
Cycle length showed no correlation with follicle size before ovulation in this sample (Spearman's rho = 0.02, p-value = 0.7).
Interpretation
This secondary analysis followed 107 women with normal fertility through 282 cycles at eight European centers. Follicle growth rate was consistent across women and centers. The size a follicle reached just before ovulation varied from cycle to cycle in the same woman. The variation came mainly from how long the growth process ran, cycle to cycle. The authors note the study did not include women with fertility problems, by design. The findings support further research into what this cycle-to-cycle variation means for reproductive outcomes.
RRM Context
Ultrasound checks for couples with fertility problems often rely on just one cycle. The authors note this could give a misleading picture of follicle growth. Follicle size changed within the same woman from cycle to cycle. Restorative reproductive medicine reads findings across several cycles of charting.
Our editorial summary of this paper, not the article's abstract.
Abstract
Background
To assess the amount of variability in ovarian follicular growth rate and maximum follicular diameter related to different centers, women and cycles of the same women in a multicenter observational study of follicular growth.
Methods
Secondary analysis of a prospective cohort study from eight centers in Europe. There were 533 ultrasound examinations in 282 cycles of 107 women with normal fertility. A random effects model with center, woman and cycle as hierarchical units of variation was used to analyze mean follicular diameter on days preceding ovulation.
Results
Follicular growth did not differ by center. There was homogenous growth across women and cycles, and the maximum follicular diameter before ovulation varied substantially across cycles but not across women. Many (about 40%) women had small maximum follicular diameter on the day before ovulation (<19 mm). Pre-ovulatory cycle length was not related to maximum follicular diameter.
Conclusion
In normal fecundity, there is a substantial variation in maximum follicular diameter from cycle to cycle based on variation in the duration of follicular development, but the variation could not be explained by different characteristics of different women. Explanation of variation in follicular growth has to be found on the cycle level.
