Table 4. Association between duration of expulsive efforts and risk of severe PPH–univariable and multivariable analysis (n = 1699; 998 severe PPH and 701 controls).

Variables	crude OR OR[95% CI]	Adjusted OR* OR[95% CI]	p
Duration of expulsive efforts (minutes)
≤18	1	1
]18–27]	1.56 [1.21–2.01]	1.37 [1.02–1.85]
]27–37]	2.08 [1.55–2.81]	1.41 [0.99–2.02]
>37	2.60 [1.86–3.65]	1.59 [1.06–2.39]
Missing	1.00 [0.76–1.32]	0.62 [0.43–0.90]	<0.01
Maternal age
≤25	0.95 [0.77–1.91]	1.08 [0.83–1.41]
26–35	1	1
>35	1.31 [1.22–1.52]	1.20 [0.80–1.81]	0.61
Gestational age
<37 weeks	0.82 [0.50–1.35]	1.35 [0.73–2.51]
37–40	1	1
≥41	1.58 [1.25–2.00]	1.04 [0.78–1.40]	0.62
Induction of labor	1.49 [1.17–1.87]	1.15 [0.85–1.56]	0.36
Total dose of oxytocin (IU)
0	1	1
]0–0.57]	1.24 [0.93–1.66]	1.21 [0.85–1.72]
]0.57–1.68]	1.33 [1.01–1.75]	1.23 [0.87–1.74]
>1.68	2.52 [1.95–3.27]	1.82 [1.27–2.60]	<0.01
Epidural	1.28 [0.97–1.68]	0.67 [0.47–0.97]	0.03
Duration of previous phases of labor (for one hour)	1.12 [1.08–1.15]	1.04 [1.00–1.09]	0.05
Mode of delivery
Spontaneous	1	1
Forceps	2.72 [2.16–3.43]	1.98 [1.47–2.66]
Vacuum	1.13 [0.80–1.60]	0.75 [0.49–1.15]	<0.01
Episiotomy	2.14 [1.75–2.61]	2.62 [1.91–3.59]	<0.01
Perineal tears	1.12 [0.91–1.38]	2.09 [1.53–2.86]	<0.01
Prophylactic postpartum oxytocin administration	0.51 [0.41–0.62]	0.44 [0.34–0.57]	<0.01
Birth weight (grams)
≤3000	0.60 [0.47–0.77]	0.66 [0.49–0.89]
3001–3500	1	1
3501–4000	1.58 [1.25–1.99]	1.26 [0.96–1.65]
>4000	3.40 [2.09–5.52]	2.80 [1.61–4.86]	<0.01
Annual number of deliveries in the unit
≤1500	0.60 [0.44–0.81]	0.73 [0.40–1.34]
1501–3000	0.62 [0.46–0.82]	0.73 [0.40–1.34]
>3000	1	1	0.58
Group of randomization in PITHAGORE6 trial	0.94 [0.78–1.14]	0.91 [0.66–1.26]	0.58

* multilevel logistic model regression including all variables in the table