. 2022 Sep 16;101(12):1422–1430. doi: 10.1111/aogs.14447

TABLE 3.

Crude and adjusted relative risk for labor induction among singleton births in Iceland in 1997–2018 by calendar time stratified by gestational and maternal age (N = 85 620)

Crude model	n	Ref	2002–2007		2008–2013		2014–2018
	n		RR	95% CI	RR	95% CI	RR	95% CI
	85 620		1.12	1.05–1.17	1.63	1.55–1.71	1.91	1.81–2.01
Adjusted stepwise
+ Sociodemographic ^a	85 620	Ref	1.10	1.05–1.16	1.66	1.58–1.75	1.95	1.85–2.05
+ Hypertension ^b	85 620	Ref	1.10	1.04–1.16	1.61	1.53–1.69	1.85	1.76–1.95
+ Gestational diabetes ^c	85 620	Ref	1.07	1.02–1.13	1.55	1.47–1.63	1.66	1.54–1.72
Fully adjusted model ^d	85 620	Ref	1.02	0.97–1.08	1.40	1.33–1.47	1.43	1.35–1.51
Stratified by gestational age ^d
Early‐term (37⁺⁰–38⁺⁶ weeks)	11 595	Ref	1.07	0.92–1.24	1.68	1.46–1.93	1.62	1.40–1.88
Full‐term (39⁺⁰–40⁺⁶ weeks)	46 554	Ref	1.03	0.93–1.14	1.54	1.40–1.69	1.39	1.26–1.53
Late‐term (41⁺⁰–41⁺⁶ weeks)	18 771	Ref	0.95	0.85–1.05	1.80	1.64–1.98	2.06	1.86–2.27
Post‐term (>42⁺⁰ weeks)	3280	Ref	1.09	0.98–1.21	1.15	1.01–1.31	1.33	1.15–1.54
Stratified by maternal age ^e
≤25 years	19 214	Ref	1.00	0.90–1.12	1.49	1.34–1.67	1.58	1.41–1.78
26–30 years	27 591	Ref	1.02	0.92–1.12	1.43	1.30–1.58	1.49	1.35–1.65
31–34 years	19 888	Ref	0.95	0.85–1.03	1.41	1.27–1.57	1.27	1.13–1.42
35–39 years	14 755	Ref	0.94	0.83–1.07	1.31	1.17–1.48	1.27	1.12–1.44
≥40 years	4172	Ref	0.88	0.71–1.11	1.35	1.09–1.67	1.53	1.23–1.91

^{^a}

Model adjusted for sociodemographic covariates: parity, age, citizenship, residency, marital and employment status.

^{^b}

Model adjusted for sociodemographic covariates and hypertension.

^{^c}

Model adjusted for sociodemographic covariates, gestational diabetes and gestational diabetes.

^{^d}

Model adjusted for sociodemographic covariates and the following labor indications: preeclampsia/eclampsia, hypertension, diabetes (gestational and pre‐existing), fetal distress, cholestasis, Rh immunization, maternal wellbeing, other and fetal wellbeing, other.

^{^e}

Model adjusted for parity, citizenship, residency, marital/employment status and gestational age; and the following labor indications: preeclampsia/eclampsia, hypertension, diabetes (gestational and pre‐existing), fetal distress, cholestasis, Rh immunization, maternal wellbeing, other and fetal wellbeing, other.