2.4. Determination of noncholesterol steroids in serum

Serum noncholesterol steroids from mothers or newborns' cord blood were analyzed using a method modified from which we previously described (Liu et al., ²⁰¹⁵, ²⁰¹⁷). In brief, total serum lipids were extracted using a mixture of chloroform and methanol (2:1, vol/vol) with the addition of 5α‐cholestane as an internal standard, followed by saponification. Steroids in the nonsaponified fraction were converted to its TMS‐ether derivatives by a commercial TMS reagent (Sigma). The analysis of steroids TMS‐ether derivative was performed in a capillary DB‐5ms (30 m × 0.25 µm, i.d. = 0.25 mm) column (Agilent) using a GC‐2010 Plus High‐end Gas Chromatograph (Shimadzu) equipped with a flame ionization detector. Serum noncholesterol steroids were calculated according to the amount of internal standard 5α‐cholestane added.