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Antral Follicle Count and Serum Follicle-Stimulating Hormone Levels to Assess Functional Ovarian Age

Chow, Gregory E. MD; Criniti, Amy R. MD; Soules, Michael R. MD

doi: 10.1097/01.AOG.0000136480.64556.90
Original Research
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OBJECTIVE: The objective of this study was 2-fold. The first was to estimate side-to-side variation in antral follicle counts. The second was to determine whether basal follicle-stimulating hormone levels on days 2, 3, and 4 of the same menstrual cycle are significantly different.

METHODS: Forty-one patients between the ages of 20 and 42 years undergoing monitoring for in vitro fertilization-embryo transfer were evaluated ultrasonographically for antral follicle number. The antral follicle counts were determined for each ovary by experienced ultrasonographers at the time of suppression check ultrasonography. In a separate study, 62 normal subjects (ages 20–25 and 40–45 years) underwent serial sequential serum follicle-stimulating hormone determinations on days 2–4 of the menstrual cycle, and these levels were compared.

RESULTS: There was no significant difference between right and left antral follicle counts (P = .30). Serial follicle-stimulating hormone values were not significantly different on days 2, 3, or 4 of the menstrual cycle (P = .22).

CONCLUSION: There is no significant difference between right-sided and left-sided antral follicle counts within the same individual. In turn, there is no significant difference in serial follicle-stimulating hormone levels on days 2, 3, or 4 of the menstrual cycle.

LEVEL OF EVIDENCE: III

In the initial evaluation of functional ovarian reserve, right-sided and left-sided antral follicle counts and basal follicle-stimulating hormone levels do not differ significantly.

From the Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Washington, Seattle, Washington.

Reprints are not available. Address correspondence to: Gregory E. Chow, MD, Fertility and Endocrine Center, 4225 Roosevelt Way NE, Suite 101, Seattle, WA 98105–6099; e-mail: gchow@u.washington.edu.

Received April 7, 2004. Received in revised form May 24, 2004. Accepted June 3, 2004.

In this era of delayed child bearing, ovarian reserve testing (assessment of functional ovarian age) is an increasingly important step in the evaluation of infertile women. Antral follicle counts have become an increasingly used tool in the evaluation of ovarian reserve in women of reproductive age. Antral follicles are defined as early Graafian follicles that are 2–10 mm in size, round to oval, echolucent-fluid-filled structures, easily imaged by ultrasonography, that represent a cohort of follicles awaiting further recruitment and stimulation by gonadotropins. The number of antral follicles counted on each ovary can be used to complement follicle-stimulating hormone (FSH) levels in ovarian reserve assessment.1–3 In some situations, however, the practitioner may not be able to adequately image both right and left ovaries. This may be due to factors such as patient body habitus, patient discomfort, stool in the colon, or location of an ovary out of the focal length of the transvaginal or transabdominal probe. In this situation, it would be clinically helpful to know whether the antral follicle count of one ovary correlates with the antral follicle count on the contralateral side.

Traditionally, FSH has had a predictive value for assessment of ovarian reserve based on measuring levels on day 3 of the menstrual cycle.4,5 In early publications day 3 was arbitrarily selected as the day that would be representative of the early follicular phase. However, in certain situations (eg, on weekend days or when patients live in remote areas), drawing FSH levels only on day 3 of the cycle may be a logistical problem. This raises questions regarding the variability of these levels during the early follicular phase of the menstrual cycle. Could a meaningful FSH level be obtained on another day in the early follicular phase?

The purpose of our study was 2-fold. We evaluated whether there was a significant side-to-side difference in ovarian antral follicle counts. In turn, we investigated whether there are significant variations in follicle-stimulating hormone levels drawn on days 2, 3, or 4 of the menstrual cycle.

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MATERIALS AND METHODS

The study was an institutional review board-approved retrospective analysis from a tertiary care university clinic setting. For the antral follicle assessment, 41 infertile patients ranging in age from 20 to 42 years were selected from our in vitro fertilization-embryo transfer (IVF-ET) database. The period of enrollment for these patients extended from September 1999 through January 2001. The inclusion criteria were participation in an IVF-ET cycle, presence of both ovaries, no history of ovarian surgery, and the ability to image both ovaries by ultrasonography. Antral follicle counts for right and left ovaries were determined at initial ultrasound evaluation before gonadotropin stimulation by an experienced physician. Baseline ultrasound examinations, or suppression ultrasonograms, are performed at the same point in the IVF-ET cycle, after gonadotropin-releasing hormone agonist (GnRH) down regulation and before stimulation with gonadotropins. It has been demonstrated in previous studies that there is no difference in antral follicle count in patients before and after treatment with a gonadotropin-releasing hormone agonist.6 A Phillips (ATL) Ultramark 400C vaginal transducer (5.5, 6.5, 7.5 MHz) (Philips Medical Systems, Andover, MA) was used to image each ovary. Antral follicle counts were determined sequentially for right and left ovaries.

In a separate study population, 62 normal, ovulatory women (ages 20–25 and 40–45 years) were recruited for an institutional review board-approved protocol to evaluate ovarian function. The patients were recruited for enrollment from November 1996 through May 1998. Patients had serial follicle-stimulating hormone levels drawn on days 2–4 of the menstrual cycle. The follicle-stimulating hormone assay (Delfia hFSH Kit #A0710201, PerkinElmer Life and Analytical Sciences, Inc., Boston, MA) had intra-assay and interassay variability of .055 (12.0%, 22.3%) low pool, 1.05 (1.9%, 8.9%) mid pool, and 20.6 (2.9%, 8.3%) high pool.

Paired t tests were performed on the antral follicle counts using GraphPad Prism 4.00 for Windows (GraphPad Software, San Diego, CA). Significance was assigned as P < .05 for antral follicle counts. Sample size calculations were performed. Thirty-three patients were needed to detect a difference of 25% between ovaries with a power of 80%.

Serial follicle-stimulating hormone values for each patient were compared using a 1-way analysis of variance with repeated measures using GraphPad Prism 4.00 for Windows (GraphPad Software). Again, significance was assigned as P < .05.

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RESULTS

There was no significant difference in the number of antral follicles imaged on the right versus left ovary for each of the 41 patients (P = .30, r = 0.59, Fig. 1). When evaluating FSH levels, the overall values for the combination of older and younger women were compared. Mean FSH levels on cycle days 2, 3, and 4 were 7.7, 8.2, and 7.8 mIU/mL, respectively (Fig. 2A). In the combined age group, there did not seem to be significant differences in FSH levels drawn on days 2–4 of the menstrual cycle (P = .22). In addition, each of the age groups was separated into younger and older women (Fig. 2B). In the younger group (ages 20–25 years) the difference between levels on days 2, 3, or 4 were not statistically significant(P = .409). The mean FSH values on cycle days 2–4 were 4.5, 4.6, and 4.3 mIU/mL, respectively, for this group. In the group of older women (ages 40–45 years), again there was no difference in the follicle-stimulating hormone values (P = .287). As expected, the mean FSH values on cycle days 2–4 for this group were 9.9, 10.6, and 10.2 mIU/mL, respectively; considerably higher than for the younger cohort.

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DISCUSSION

Numerous studies have demonstrated a relationship between antral follicle counts and the degree of gonadotropin stimulation in controlled ovarian hyperstimulation and IVF-ET cycles. Generally it seems that with higher antral follicle counts, the ovarian response to gonadotropins improves.7–10 Thus, antral follicle counts are helpful in predicting patients who may be good or poor cycle responders. Moreover, antral follicle counts have become useful as a quantitative aid to help determine initial gonadotropin doses for IVF-ET cycles.

In all prior studies, the antral follicle count as an indication of ovarian reserve has been expressed as a total antral follicle count (the sum of the antral follicle counts in the right and left ovaries). Our data indicate that there is no significant difference between right-sided and left-sided antral follicle counts in patients with normal-appearing ovaries. Because the use of antral follicle counts is gaining increasing usefulness in the evaluation of ovarian reserve testing, this information is pertinent to the practicing clinician. In cases where one ovary is difficult to image, it would be reasonable to assume an antral follicle count equal to that of the contralateral side, provided the ovaries are thought to be normal. This extrapolation, of course, would not hold in cases where cortical tissue of the ovary has been destroyed surgically or if there is other known ovarian pathology.

A weakness of this study is the potential for internal bias among individual ultrasonographers. After determining the antral follicle count for one side, it is tempting to assign a similar number to the opposite side. Variability among examiners regarding which ovary that they habitually evaluate first helps to alleviate this problem.

Various methods of ovarian reserve testing have been established with the goal of predicting a patient's response to ovulation induction agents and her prognosis for both pregnancy and miscarriage.4,5 Basal or day 3 follicle-stimulating hormone has been extensively used as a screening method to estimate ovarian reserve.4–6 Day 3 follicle-stimulating hormone levels have been shown to be predictive of cycle outcome and overall pregnancy rates.4 Elevated levels have been associated with poor response during assisted reproductive technique cycles and decreasing pregnancy rates, indicative of an age-related decline in fertility. There are differing opinions as to what cutoff value should preclude starting an assisted reproductive technique cycle.6,11

Follicle-stimulating hormone levels do not seem to vary significantly between days 2, 3, or 4 of the menstrual cycle in normal women. It is therefore reasonable to use a level on any of these days as an assessment of ovarian reserve. This knowledge may provide the clinician and patient greater flexibility in the initial evaluation of ovarian status. Day 3 follicle-stimulating hormone levels do seem to trend slightly higher than either day 2 or day 4 levels. While there is no significant difference among any of these levels, a small difference might prompt a physician to alter his or her clinical management if he or she bases the decision-making process on an absolute cutoff value. In general, cutoff threshold values should only be interpreted in the context of intercycle and interassay variation

Antral follicle counts do not seem to vary significantly from side to side within patients. This provides basic clinical usefulness when evaluating patients with one ovary that is not easily imaged. In addition, follicle-stimulating hormone levels do not seem to vary significantly when measured between days 2–4 of the menstrual cycle. This information allows greater flexibility in the clinic setting when performing initial evaluation of ovarian reserve status.

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REFERENCES

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© 2004 by The American College of Obstetricians and Gynecologists.