Optimal timing for frozen-thawed embryo transfer: evidence from a systematic review and meta-analysis.

For multiple pregnancy rate ( Supplementary Table S4 ), while the pooled estimate was nominally significant (OR = 1.26, 95% CI: 1.03-1.55, P = 0.02), exclusion of three studies (Liang, Mao, and Wang) rendered the association non-significant, with 95% CIs crossing the null in all three scenarios; the effect, while directionally consistent, is statistically fragile and dependent on a subset of studies, with persistent high heterogeneity (I2 range: 61.42%-78.35%) further limiting confidence.

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For biochemical pregnancy rate, maternal age showed a trend toward significance (P = 0.056).

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