Natural cycle IVF produces similar implantation rates compared with stimulated IVF

Abstract

OBJECTIVE: To evaluate the fertilization, growth, and implantation rate of embryos derived from unstimulated, natural cycle IVF when compared to embryos resulting from stimulated IVF cycles. DESIGN: Retrospective analysis of embryonic data from natural and stimulated IVF cycles in women ≤ 37 years of age, conducted at a single clinic over the course of three years (2007-2009). MATERIALS AND METHODS: 667 cycles of IVF were performed on patients ≤37 yrs old from January 2007 through December 2009 representing 434 stimulated and 233 unstimulated (natural) IVF cycles. The average patient age was 34 ± 6 yrs for stimulated and 32 ± 4 yrs for natural cycle patients. Data was collected to compare normal fertilization (2PN) rates, embryonic development, and implantation rates. Chi-squared analyses were used to evaluate the relationships between these groups. RESULTS: 2PN rates of 68.3% in stimulated cycles (SC) and 72.2% in natural cycles (NC) were observed. Of these fertilized oocytes, 57.1% (SC) and 62.8% (NC) developed into good quality embryos - defined as reasonably symmetrical 8-10 cell embryos with less than 10% fragmentation on day 3, and symmetrical, vacuole-free blastocysts and early blastocysts with well defined blastoceols and inner cells masses. 728 (SC) and 111 (NC) embryos were transferred, resulting in implantation rates of 30.6% and 38.7%, respectively. Implantation rates were determined by ultrasound. There were no significant differences (P≤0.05) associated with any of the comparisons. CONCLUSION: Normal fertilization rates, developmental quality, and implantation rates do not differ significantly between unstimulated and stimulated IVF cycles. Additionally, unstimulated cycles demonstrated a trend toward a better overall outcome per oocyte. From this we conclude that a well-implemented natural cycle IVF program provides a viable treatment option for certain patients, despite the limitations in terms of oocytes retrieved per patient.