Table 6. The results of two-piecewise linear regression model.

Groups	Inflection point (hCG E2, pg/dl)	Adjusted OR (95% CI)	P-value	LRT test
Cleavage group	<31.1	1.04 (1.01–1.07)	0.022	0.029
	>31.1	0.98 (0.96–1.01)	0.297
Blastocyst group	<39.7	0.99 (0.97–1.02)	0.846	0.013
	>39.7	0.83 (0.72–0.96)	0.012

Notes.

Adjustment covariates: age (smooth), BMI, infertility duration, fertilization method, sterility classification, previous cycle attempts, basal FSH, basal LH, basal E₂, FSH on hcg day, LH on hCG day, P on hCG day, endometrial thickness on hCG day, number of retrieved oocytes, the number of inviable embryos, and the number of embryos transferred.

P < 0.05 presented a nonlinear relationship.

Abbreviations

LRT test

logarithmic likelihood ratio test

OR

odds ratios

CI

Confidence interval