The influence of the number of follicles on pregnancy rates in intrauterine insemination with ovarian stimulation: a meta-analysis.

BACKGROUND The influence of multifollicular growth on pregnancy rates in subfertile couples undergoing intrauterine insemination (IUI) with controlled ovarian hyperstimulation (COH) remained unclear. METHODS Relevant papers were identified by searching MEDLINE, EMBASE and the Cochrane Library. A meta-analysis was performed and Mantel-Haenszel pooled odd ratios (ORs) and risk differences with 99% confidence intervals (CIs) were calculated to express the relation between the number of follicles and pregnancy rates. RESULTS We included 14 studies reporting on 11 599 cycles. The absolute pregnancy rate was 8.4% for monofollicular and 15% for multifollicular growth. The pooled OR for pregnancy after two follicles as compared with monofollicular growth was 1.6 (99% CI 1.3-2.0), whereas for three and four follicles, this was 2.0 and 2.0, respectively. Compared with monofollicular growth, pregnancy rates increased by 5, 8 and 8% when stimulating two, three and four follicles. The pooled OR for multiple pregnancies after two follicles was 1.7 (99% CI 0.8-3.6), whereas for three and four follicles this was 2.8 and 2.3, respectively. The risk of multiple pregnancies after two, three and four follicles increased by 6, 14 and 10%. The absolute rate of multiple pregnancies was 0.3% after monofollicular and 2.8% after multifollicular growth. CONCLUSIONS Multifollicular growth is associated with increased pregnancy rates in IUI with COH. Since in cycles with three or four follicles the multiple pregnancy rate increased without substantial gain in overall pregnancy rate, IUI with COH should not aim for more than two follicles. One stimulated follicle should be the goal if safety is the primary concern, whereas two follicles may be accepted after careful patient counselling.