Table 5. Results of multiple linear regression analysis performed to assess the independent relationship between DNA level, the study (ours vs. Bi et al. 2008) and gestational age.

Variables	DNA level
	β	Robust SE	95% CI β	P-value
Study (ours vs Bi et al. 2008)	−103	14.4	−131; −74	0.0001
Gestational age	20.2	2.75	14.7; 25.6	0.0001
Intercept	−276	43.3	−362; −190	0.0001

The multiple linear regression analysis model adjusted for gestational age (R² = 0.42).