Table 1 OXTR genotype (rs53576) and oxytocin administration and postpartum hemorrhage for 95 vaginal births

Demographic characteristics

  Participant age (years), mean (SD)

33.1 (4.4)

33.9 (4.5)

  Primiparous, n (%)

13 (34.2)

30.0 (52.6)

Self-reported ancestry (may have 1 or more)

  European, n (%)

35 (92.1)

 44 (77.2)

  Latin American, n (%)

2 (5.3)

 6 (10.5)

  Asian, n (%)

2 (5.3)

 10 (17.5)

  African, n (%)

1 (2.6)

 0 (0.0)

  Other, n (%)

3 (7.9)

 4 (7.0)

  Case, n (%)

19 (50.0)

 20 (35.1)

  Control, n (%)

19 (50.0)

 37 (64.9)

Antenatal characteristics

  Body Mass Index at delivery (kg/m²), mean (SD)

30.2 (4.2)

31.6 (5.5)

  Gestational diabetes, n (%)

6 (15.8)

9 (15.8)

  Hypertension /preeclampsia (without severe features), n (%)

2 (2.3)

7 (12.3)

  Fibroid uterus, n (%)

0 (0.0)

2 (3.5)

  Anemia during pregnancy, n (%)

7 (18.9)

15 (26.3)

Labor and Birth Characteristics

  Spontaneous onset of labor, n (%)

20 (52.6)

27 (47.3)

  Fever/ suspected intrapartum infection, n (%)

2 (5.3)

4 (7.0)

  IV antibiotics during labor, n (%)

14 (36.8)

13 (22.8)

  Gestational age at birth (weeks), mean (SD)

39.6 (1.3)

39.9 (1.2)

  No oxytocin in labor, n (%)

  Oxytocin in labor, n (%)

20 (52.6)

18 (47.4)

20 (35.1)

37 (64.9)

  Total oxytocin used in labor (Units), median (IQR)

5.3 (0.6–12.6)

3.7 (1.3–12.3)

  Total oxytocin used postpartum (Units), median (IQR)

10 (10–23.6)

15.0 (10.0–25.0)

  Maximum dose oxytocin used in labor (mU/min), median (IQR)

9.5 (6.0–17.0)

12 (6.0–17.0)

  Duration oxytocin used in labor (hours), median (IQR)

13.0 (3.9–20.9)

11.4 (6.9–19.0)

  Duration first stage labor (hours), median (IQR)

10.5 (5.5–19.7)

11.6 (7.7–18.3)

  Duration second stage labor (hours), median (IQR)

0.8 (0.3–1.8)

1.0 (0.4–1.9)

  Length of third stage of labor (minutes), mean (SD)

11.1 (12.5)

9.0 (9.1)

  Female infant sex, n (%)

21 (55.3)

27 (47.4)

  Newborn weight (grams), mean (SD)

3396.4 (697.4)

3481.3 (637.0)

Postpartum Characteristics

  Postpartum blood loss >  = 400 mL, n (%)

18 (47.4)

43 (75.4)**

  Postpartum blood loss >  = 1000 mL, n (%)

3 (7.8)

11 (19.3)

  Total blood loss (mL), median (IQR)

400 (200–600)

500 (423–800)**

  Retained placenta/fragments, n (%)

5 (13.2)

5 (8.8)

Medications used for bleeding/hemorrhage, n (%)

  Active management of third stage labor (Oxytocin IM/IV for prevention)

34 (89.5)

47 (82.5)

  Active management of third stage labor (Oxytocin IM/IV for prevention)

15 (42.9)

25 (43.8)

  Received one or more second-line pharmaceutical treatment (misoprostol, methylergonovine, carboprost tromethamine or tranexamic acid)

12 (31.8)

33 (57.9)*

Other hemorrhage interventions, n (%)

  Bimanual compression

3 (7.8)

13 (22.8)*

  Dilatation and curettage

1 (2.6)

3 (5.3)

  Bakri Balloon

0 (0.0)

2 (3.5)

  Difference in hemoglobin (third trimester to lowest postpartum value in mg/dL), mean (SD)

-0.6 (1.3)

-1.6 (2.2)*

  Received iron infusion or blood transfusion, n (%)

3 (7.8)

9 (15.8)

  No genital trauma (none/no repair needed), n (%)

14 (40.0)

13 (22.8)