Clinical Review

7 easy steps to evaluating subfertility

OBG Manag. 2002 April;14(4):74-86

References

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In a population-based study, the probability of pregnancy positively correlated with increasing sperm density up to 40×10⁶/mL, with no further correlation above this concentration.²³ The proportion of morphologically normal sperm, as measured using WHO criteria, strongly correlated to pregnancy, independent of sperm concentration.²³

Combined semen parameters also were useful.²⁴ Using ROC curves and strict criteria for normal morphology, the thresholds (ejaculate) distinguishing fertile from subfertile men were 36 million total motile sperm, 6 million total normal sperm, and 5 million total normal motile sperm.²⁴

Calculating prognosis

How do we quantify our estimate of a couple’s prognosis for treatment-independent live birth? Using the patient described at the beginning of this article as an example, we first estimate the chance of spontaneous conception within 12 months leading to live birth. In this case, as Table 1 shows, it would be 28%, since the patient has not been treated by other physicians.³ (If she had, the chance of treatment-independent live birth would be 14%.) Subsequent steps include:

Adjust maternal age. For a patient such as ours, who is seeking treatment for the first time, no adjustment is necessary. (For secondary care, however, the chance of treatment-independent live birth would decrease by a factor of 0.95 for each year beyond 30, as Table 1 indicates. Thus, we would adjust our estimate for our 35-yearold patient using the following formula: 14%×0.95⁵=10.8%.)
Adjust for the duration of subfertility. For the same patient who is seeking primary care for 24 months of subfertility, the formula would be: 28%×1.5=42%. (The formula for a similar patient undergoing secondary care would be: 10.8%×1.7=18.3%.) (See Table 1.)
Consider prior pregnancy in the partnership. Since there has been none in the patient seeking primary care, our estimate remains at 42%. However, if the couple had previously conceived a child, the formula would be: 42%×1.5=63%. (For the patient seeking secondary care, the formula is as follows: 18.3%×1.8=33%.) (See Table 1.)

Table 2 shows additional adjustment factors in the event that a male defect, endometriosis, or a tubal defect is diagnosed. For example, if tubal disease is diagnosed, the formula for our patient would be: 42%×0.5=21%. (The formula for a patient undergoing secondary care would be: 18.3%×0.5=9.1%.) If more than one of these conditions is diagnosed, the clinician would use only 1 adjustment factor.

TABLE 1

The effect of historical factors on treatment-independent live birth

	Primary care	Secondary care
Baseline prognosis^a	28%	14%
Modifying factors	Relative chance^b	Relative chance^b
Age of female partner ≤30 years	1.4 (1.0-1.8)	1.5 (1.1-2.2)
Adjustment factor for each—additional year >30	—	0.95 (0.92-0.98)
Duration of subfertility <24 months=primary care 24-36 months=secondary care	1.5 (1.2-2.1)	1.7 (1.1-2.5)
Adjustment factor for each additional 12 months of subfertility >36 months	—	0.82 (0.76-0.88)
Previous pregnancy in partnership	1.5 (1.1-2.1)	1.8 (1.2-2.7)
NOTE: Numbers in parenthesis are 95% confidence intervals
^a After 12 months of unprotected intercourse
^b Versus entire untreated subfertility population
SOURCE: Collins JA, et al. The prognosis for live birth among untreated infertile couples. Fertil Steril. 1995;64:22-28.

TABLE 2

Effect of diagnostic factors on treatment-independent live birth

Diagnosis	Relative chance of live birth*
Male defect (sperm density <20×10⁶ or motility <40%)	0.5 (0.3-0.8)
Endometriosis (aggregate figure for all stages)	0.4 (0.2-0.9)
Tubal defect (aggregate figure for any defect, either bilateral/unilateral or partial/complete)	0.5 (0.4-0.6)
* Versus entire untreated subfertility population.
SOURCE: Collins JA, et al. The prognosis for live birth among untreated infertile couples. Fertil Steril. 1995;64:22-28.

A few caveats

Even after a thorough diagnostic workup, a number of elements essential to successful reproduction will remain unknown. Thus, the estimate of treatment-independent live birth has only limited accuracy, since our assessments do not determine whether spermatozoa ascend the fallopian tube, the oocyte is released into the tubal ampulla, fertilization of the oocyte occurs, or whether the developing embryo enters the uterine cavity for implantation. Nevertheless, our model is useful in establishing a couple’s baseline fertility by giving an objective estimate of fertility prognosis during diagnostic investigation. It also serves as an important benchmark for determining which therapeutic options are most appropriate and cost-effective.

The authors report no financial relationship with any companies whose products are mentioned in this article.