Table 3 Part of variables investigated in analysis

Maternal age (y)

age of delivery; categorized into four groups: < 18, 18–34.9, 35–39.9 and ≥ 40 years.

Parity

grouped into no previous deliveries (0), 1–2 previous deliveries, and ≥ 3 previous deliveries.

BMI (kg/m²)

low weight < 18.5; normal: 18.5–24.9; overweight: 25–29.9; obesity≥30.

Hypertensive disorders of pregnancy

categorized into gestational hypertension, preeclampsia and eclampsia; gestational hypertension was defined as only if she did not have codes for pre-existing hypertension or preeclampsia or eclampsia.

Anemia

hemoglobin< 9 g/dL before delivery.

Thrombocytopenia

platelet count< 100*10⁹/L.

Prolonged labor

prolonged first stage of labor was determined as deviation of cervical dilatation from the normal rate of 1 cm/hour in the active phase or slow progress of the descent of the presenting part through birth canal; prolonged second stage of labor was> 1 h from complete cervical dilation to delivery if multiparous and > 2 h between complete cervical dilation and delivery if nulliparous.

Precipitate labor

3 h or less from the onset of regular contractions to birth.

Macrosomia

substituted by a birthweight of ≥4 kg.