Interpregnancy Interval and IVF Treatment Outcomes

When it comes to the interpregnancy interval (IPI) following a clinical pregnancy loss (CPL) during in vitro fertilization (IVF) treatment, finding the right timing has remained a subject of debate. A recent retrospective cohort study conducted in China aimed to shed light on this matter by evaluating the association between various IPI lengths and the outcomes of the next frozen embryo transfer (FET). This study suggests that the timing of the interpregnancy interval is a crucial factor in achieving successful pregnancy outcomes, particularly for women undergoing IVF treatment after experiencing a clinical pregnancy loss.

This study was published in JAMA Network Open by Ze Wang and colleagues. This was a retrospective cohort study conducted at the Center for Reproductive Medicine of Shandong University in China. The study aimed to evaluate the association between different interpregnancy interval (IPI) lengths following a preceding clinical pregnancy loss (CPL) and the subsequent pregnancy outcomes of the next frozen embryo transfer (FET).

The study included women who had undergone frozen-thawed blastocyst transfer within 1 year after experiencing a CPL during in vitro fertilization (IVF) treatment. The data were collected from women who received IVF treatment between July 1, 2017, and June 30, 2022. Follow-up for pregnancy outcomes was completed for all participants on March 31, 2023.

The study included a total of 2433 women with a mean age of 31.8 years. These women were divided into three groups based on the length of their interpregnancy interval following a CPL: less than 3 months, 3 to less than 6 months, and 6 to 12 months. The study assessed several key pregnancy outcomes related to the next FET after a preceding CPL. These outcomes included:

• Clinical Pregnancy: The achievement of a clinical pregnancy following the FET.
• Live Birth: The successful delivery of a live infant following the FET.
• Healthy Live Birth: The delivery of a live infant without adverse health conditions.
• Total Pregnancy Loss: The occurrence of pregnancy loss, including both clinical and subclinical losses.

The outcomes were evaluated by calculating adjusted odds ratios (AORs) to determine the association between the length of interpregnancy intervals and these pregnancy outcomes. The study focused on comparing the outcomes between women with shorter IPIs (<3 and 3 to <6 months) and those with an IPI of 6 to 12 months.

Compared with women with an IPI of 6 to 12 months, those with shorter IPIs (<3 and 3 to <6 months) had the following results:

• Clinical Pregnancy:
  • An IPI of less than 3 months: Adjusted Odds Ratio (AOR) of 0.70 (95% CI: 0.53-0.92)
  • An IPI of 3 to less than 6 months: AOR of 0.79 (95% CI: 0.65-0.95)
• Live Birth:
  • An IPI of less than 3 months: AOR of 0.64 (95% CI: 0.48-0.85)
  • An IPI of 3 to less than 6 months: AOR of 0.74 (95% CI: 0.61-0.90)
• Healthy Live Birth:
  • An IPI of less than 3 months: AOR of 0.63 (95% CI: 0.46-0.87)
  • An IPI of 3 to less than 6 months: AOR of 0.79 (95% CI: 0.64-0.98)
• Total Pregnancy Loss:
  • An IPI of less than 3 months: AOR of 1.87 (95% CI: 1.31-2.67)
  • An IPI of 3 to less than 6 months: AOR of 1.29 (95% CI: 1.00-1.66)

These results indicate that shorter interpregnancy intervals (<3 and 3 to <6 months) were associated with a decreased likelihood of achieving clinical pregnancy, live birth, and healthy live birth. Additionally, women with shorter IPIs had a higher risk of total pregnancy loss compared to those with an IPI of 6 to 12 months.

Delaying the next frozen embryo transfer for at least 6 months after a preceding clinical pregnancy loss was found to be associated with more favorable pregnancy outcomes, emphasizing the significance of interpregnancy interval length in the context of IVF treatment following a CPL. Further prospective studies are warranted to validate and expand upon these findings.

Reference: Wang, Z., Meng, Y., Shang, X., Suo, L., Zhao, D., Han, X., Yang, M., Yin, M., Miao, H., Wang, Y., Yang, H., Yu, Y., Wei, D., & Chen, Z.-J. Interpregnancy interval after clinical pregnancy loss and outcomes of the next frozen embryo transfer. JAMA Network Open, 2023;6(10):e2340709. https://doi.org/10.1001/jamanetworkopen.2023.40709