Minimum number of sperm needed to obtain an intrauterine insemination pregnancy

Abstract

OBJECTIVE: Intrauterine insemination (IUI) with partner's sperm is a useful treatment for mild male factor, cervical factor infertility, as well as an adjunctive therapy among ovulation induction cycles. Previous studies washed the semen specimen with Sperm Wash Medium® (SWM) and resuspended the entire pellet (motile and nonmotile sperm) along with cellular debris in ∼ 0.2 to 0.4 mL of SWM. Patients that received these washed pellets collectively had a 10% pregnancy rate (PR). The possibility exists that contaminates from the nonmotile sperm and cellular debris may be deleterious to the motile spermatozoa, thus reducing the actual number of viable sperm that reach the ovulated oocyte. With the use of a gradient wash to separate the motile sperm from the detritus, is it possible to ascertain if there is a minimum number of motile sperm necessary to obtain a pregnancy? The objective of this study was to determine the relationship between sperm concentration and PR. DESIGN: A retrospective, observational analysis of IUI data collected at our tertiary care hospital. MATERIALS AND METHODS: Data were collected between mid -2005 to mid -2007 representing all patients undergoing IUI cycles in our practice. Information on 527 cycles was available for the analysis. After eliminating donor cycles and cycles with missing data, 365 cycles were available for analysis. Sperm preparations were performed with an ALLGrad® separation method. Total motile sperm concentrations of the IUI's were divided into quartiles for comparisons. These quartiles/inseminations doses were 1) < 6.7 million/mL; 2) 6.7 – 16.6 million/mL; 3) 16.7 – 32.5 million/mL; and 4) > 32.5 million/mL. To isolate the effects of sperm concentration, other known factors which impact pregnancy rates were examined. Factors such as age, body mass index, gravida, stimulation regime, attending physician and sperm motility were considered separately. Then the combined effect of multiple factors on pregnancy rate was assessed using logistic regression. RESULTS: The pregnancy rates for quartiles one through four were 8.6%, 17.2%, 17.8%, and 20.2%, respectively. The logistic regression models confirm these results after adjusting for the age of the patient. CONCLUSIONS: These data suggest that a threshold number of sperm may exist to optimize IUI success and that the minimum total number of motile sperm needed is approximately 6.7 million per insemination.