Trends in risk factors associated with the increasing labor induction rate: A nationwide register study in Finland 2005–2023

Abstract

Introduction

Induction of labor (IOL) rates have been increasing in high‐income countries. Although IOL aims to reduce maternal and neonatal morbidity, the benefits for many common indications remain uncertain. Because IOL may also have disadvantages and place a burden on the health‐care system, it is important to clarify the factors underlying the rising national IOL rates.

Material and Methods

This descriptive study included all singleton births in cephalic presentation delivered at 37⁺⁰ gestational weeks or later between January 1, 2005, and December 31, 2023, in Finland. Data from the Finnish Medical Birth Register were used to examine temporal trends in maternal characteristics, gestational age at delivery, pregnancy complications, and other pregnancy‐related problems across three periods: 2005–2010, 2011–2016, and 2017–2023. Induced deliveries were analyzed separately. Risk ratios with 95% confidence intervals were calculated to describe changes over time, and odds ratios with 95% confidence intervals were estimated to assess associations between IOL and risk factors. Logistic regression models were adjusted for maternal age, body mass index (BMI), and parity.

Results

The study sample included 880 478 births. The IOL rate doubled from 18% to 36%. In the IOL group, the most prevalent and increasingly common factors were maternal age ≥35 years, BMI ≥30 kg/m², and gestational diabetes. Prelabor rupture of membranes, fear of childbirth, and other pregnancy‐related problems—despite their lower overall proportions—showed the steepest increases. Similar but less pronounced trends were seen in the total study cohort. The odds of IOL remained stable across the study periods for maternal age ≥35 years, BMI ≥30 kg/m², gestational diabetes, prelabor rupture of membranes, fear of childbirth, and other pregnancy‐related problems; and all associations remained statistically significant after adjustment. The proportion of post‐term pregnancy decreased significantly in both the total study cohort and the IOL group. In the IOL group, gestational age at birth shifted from post‐term to late‐ and full term.

Conclusions

The main contributors to the increasing IOL rate were the increased prevalence of advanced maternal age, obesity, and gestational diabetes. The increases in the prevalence of other IOL indications were less extensive.

In this nationwide Finnish register study, the doubling of the induction of labor rate (2005–2023) was associated with advanced maternal age, obesity, and gestational diabetes mellitus, and a shift toward earlier delivery. Prelabor rupture of membranes, fear of childbirth, and other pregnancy‐related problems—despite their lower prevalences—showed the steepest increases.

Abbreviations

BMI

body mass index

GDM

gestational diabetes mellitus

IOL

induction of labor

LGA

large for gestational age

OR

odds ratio

PROM

prelabor rupture of membranes

RR

risk ratio

SGA

small for gestational age

Key message.

The doubling of the induction of labor rate in Finland from 2005 to 2023 coincided with increases in advanced maternal age, obesity, and gestational diabetes mellitus (GDM), and with more active management of common pregnancy complications such as late‐term pregnancies.

1. INTRODUCTION

Induction of labor (IOL) rates have increased in high‐income countries over the past decades, with the magnitude of the increase and current rates varying between countries. In Finland, the IOL rate doubled from 18% in 2005 to 36% in 2023. ¹ A similar trend has been noted in other Nordic countries—Sweden, Norway, and Denmark—where IOL rates in 2023 ranged from 23% to 31% (Mika Gissler, personal communication 10/2025), and in regions such as Australia, the United States, and the United Kingdom, where the latest published national IOL rates for the period 2022–2023 were 43%, 32%, and 33%, respectively. ² , ³ , ⁴ , ⁵ , ⁶

In previous cohort studies, higher IOL rates have been associated with increasing maternal age and obesity, ⁷ , ⁸ , ⁹ , ¹⁰ higher prevalence of pregnancy complications, ⁸ , ⁹ , ¹⁰ and changes in clinical practice. ⁷ , ⁸ , ¹⁰ , ¹¹ , ¹² The general aim of IOL is to reduce maternal and neonatal morbidity. However, based on systematic reviews, ¹³ , ¹⁴ meta‐analyses, ¹⁵ , ¹⁶ , ¹⁷ and individual randomized controlled trials, ¹⁸ , ¹⁹ the evidence supporting the benefits of IOL varies across common indications. In post‐term pregnancies, IOL at 41 gestational weeks (gw) decreased the perinatal mortality compared with expectant management until 42 gw, and the number needed to treat (NNT) ranged from 326 to 426. ¹³ , ¹⁴ , ¹⁶ Expedited IOL after prelabor rupture of membranes (PROM) at term reduced the neonatal intensive care unit (NICU) admission rate (with NNT being 23) and halved the risk of maternal infectious morbidity without increasing the risk of cesarean delivery compared with conservative management. ¹³ , ¹⁴ Planned early delivery significantly decreased the risk of severe maternal morbidity or mortality in women with hypertensive disorders compared with expectant management (with NNT of 51–71 for HELLP [hemolysis, elevated liver enzymes, and low platelet count] syndrome or eclampsia), and was not associated with increased risk of neonatal respiratory distress syndrome after 37 gw. ²⁰ , ²¹ , ²² In pregnancies with suspected macrosomia, particularly in women without diabetes, evidence comparing IOL with expectant management remains inconsistent. ²³ In this context, randomized trials suggest that IOL reduces shoulder dystocia without affecting brachial plexus injury. Cesarean section rates are similar or lower with IOL, whereas third‐ and fourth‐degree perineal tears may be similar or increased. ¹³ , ¹⁴ , ¹⁸ The evidence of the advantage of IOL in women with high body mass index (BMI) is mixed considering the cesarean delivery and NICU admission rates. ¹³ , ¹⁴ , ¹⁷ In addition, IOL before 39 gw in women of advanced age has not decreased the cesarean delivery rate or the risk of adverse neonatal outcomes. ¹⁹

IOL is associated with higher complication rates; however, these outcomes may partly reflect the underlying indications—such as pregnancy complications—rather than the intervention itself. Furthermore, compared with spontaneous onset of labor, IOL may increase the likelihood of poor birth experience, especially if it results in an instrumental vaginal delivery or urgent cesarean section. ²⁴ Lastly, IOL may increase health‐care costs and the workload for perinatal care. ²⁵

Given the heterogeneous benefits of IOL across common indications, alongside its potential harm and health‐care burden, it is essential to identify the factors underlying the increasing national IOL rate. In this descriptive register‐based cohort study, we examined temporal trends in IOL prevalence by maternal characteristics, pregnancy complications, and gestational age at delivery among singleton cephalic births at 37–43 gw in Finland from 2005 to 2023, during which the IOL rate doubled. The aim of this study was to clarify whether the increasing IOL rate was related to temporal changes in maternal characteristics, pregnancy complications, and clinical practices.

2. MATERIAL AND METHODS

2.1. Study design

This population‐based cohort study included all live births or stillbirths in Finland between January 1, 2005, and December 31, 2023. The study sample comprised singleton hospital births at ≥37 gw in cephalic presentation, with elective cesarean sections and forceps deliveries excluded (Figure 1). Forceps‐assisted deliveries were excluded, as the procedure is rare in Finland and is mainly used in breech presentations in cases of head entrapment. Furthermore, register data on fetal presentation in forceps deliveries are limited.

FIGURE 1.

Flowchart of the study periods. *Excluded pre‐term births, multiple gestations, breech presentations, forceps‐assisted deliveries, elective cesarean sections and out of hospital births. IOL, induction of labor.

The data used in this study were obtained from the Finnish Medical Birth Register (MBR), which has high data accuracy and coverage, ²⁶ maintained by the Finnish Institute for Health and Welfare. The MBR contains comprehensive information on all births with a birthweight ≥500 g or gestational age ≥22⁺⁰ weeks. The dataset included patient prenatal characteristics, obstetric history, information on deliveries, pregnancy and delivery complications, perinatal outcomes, and the diagnoses of parturients and neonates up to 7 days postpartum or until discharge. The data were prospectively collected during antenatal and perinatal care from maternity and neonatal units. Most of the variables were recorded by a midwife. The study variables based on diagnosis codes classified according to the Finnish implementation of the 10th Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD‐10) codes were determined by an obstetrician, gynecologist, or neonatologist (Table S1).

The national voluntary first‐trimester combined screening began on January 1, 2007. In 2007, the participation rate of pregnant women was 58%, whereas by 2013, it had increased to 99%. Before 2007, the estimation of gestational age might have varied between hospital districts. Data collection for pre‐pregnancy BMI (kg/m²) began on January 1, 2004. However, these data have been reported by all birth hospitals since October 2005. Obesity was defined as a pre‐pregnancy BMI ≥30 kg/m². Advanced maternal age was defined as maternal age ≥35 years at delivery. Smoking status was categorized into two groups: nonsmokers and pregnant women who reported smoking at some point during pregnancy. Smoking data were missing for 3.3% of the participants. Anemia during pregnancy was defined by hemoglobin levels <100 g/L.

Early‐term pregnancy was defined as 37⁺⁰–38⁺⁶ gw; full‐term pregnancy, as 39⁺⁰–40⁺⁶ gw; late‐term pregnancy, as 41⁺⁰–41⁺⁶ gw; and post‐term pregnancy, as ≥42⁺⁰ gw. Gestational diabetes mellitus (GDM) was diagnosed based on a 75‐g 2‐h oral glucose tolerance test using the following thresholds: 0 h, ≥5.3 mmol/L; 1 h, ≥10.0 mmol/L; and 2 h, ≥8.6 mmol/L. In 2008, as a result of the recommendation of the National Current Care Guidelines, universal gestational diabetes screening was implemented, replacing the former risk‐based screening. ²⁷ , ²⁸ , ²⁹ The change in practice resulted in an increase in the prevalence of GDM.

The “hypertensive disorders of pregnancy” composite encompassed pregnancy‐specific hypertension ICD‐10 codes: pregestational hypertension, gestational hypertension, and preeclampsia. “Large for gestational age” (LGA) was recorded if it was suspected during antenatal care (ultrasonography‐based estimated fetal weight > +2 SD) or if an LGA diagnosis was entered at birth. Similarly, “small for gestational age” (SGA) was recorded if it was suspected during antenatal care (estimated fetal weight < −2 SD) or if an SGA diagnosis was entered at birth. Thus, classification was based on antenatal suspicion or registered birth diagnosis rather than on birthweight standardized for gestational age. The “suspected placental insufficiency” composite comprised the following diagnoses: supervision of pregnancy with other poor reproductive history, SGA, signs of fetal hypoxia, and oligohydramnios. The PROM composite included ICD‐10–based diagnostic categories: PROM with onset of labor within 24 h, PROM with onset after 24 h, unspecified PROM, and delayed delivery after membrane rupture. The “other pregnancy‐related problems” composite included diagnoses of psychosocial problems, fatigue, and symphyseolysis (Table S1).

2.2. Labor induction practices in Finland

Pregnancy management for women with diabetes follows the national guidelines. ²⁷ , ²⁸ , ²⁹ Delivery for women with pregestational diabetes is generally advised between 38 and 40 gw, although IOL is often required earlier owing to pregnancy complications. For women with GDM receiving pharmacological treatment, guidelines recommend delivery between 38 and 40 gw; for women with diet‐treated GDM, delivery is recommended before 41⁺⁵ gw or earlier in those with suspected macrosomia. Cesarean section is recommended when the estimated fetal weight exceeds 4500 g in women with pregestational diabetes and in those with pharmacologically treated GDM. ²⁸ For women with hypertensive disorders, planned delivery is recommended between 37⁺⁰ and 40⁺⁰ gw, provided that the maternal and fetal statuses remain stable according to the 2021 guideline. ³⁰ IOL is generally initiated within 24 h in pregnancies with PROM occurring after 37 gw and earlier if any sign of infection or fetal distress is found.

There are currently no national guidelines defining the recommended timing of IOL in pregnancies complicated by intrahepatic cholestasis, maternal obesity, or post‐term gestation. International recommendations are generally followed, although clinical practice may differ between maternity hospitals. IOL is typically performed between 37 and 40 gw for intrahepatic cholestasis of pregnancy, around 40 gw for obese women, and at 41–42 gw for uncomplicated post‐term pregnancies.

2.3. Statistical analysis

Continuous variables are presented as means with standard deviations for normally distributed data and as medians with interquartile ranges for skewed data. Categorical variables are presented as frequencies and percentages. Certain continuous variables (maternal age, BMI, and gestational age) were dichotomized for categorical analysis. Temporal trends in maternal characteristics, gestational age, and pregnancy complications were analyzed across three periods: 2005–2010 (first period), 2011–2016 (second period), and 2017–2023 (last period). Birth rates were also examined in relation to gestational age to evaluate potential shifts in the timing of IOL. Data on induced deliveries were analyzed separately. Risk ratios (RRs) with 95% confidence intervals were calculated to describe changes over time, and odds ratios (ORs) with 95% confidence intervals were estimated to assess associations between IOL and risk factors. RRs were analyzed to compare the periods 2017–2023 and 2005–2010. A two‐tailed p value <0.05 was considered statistically significant. Adjusted ORs with 95% CIs were estimated only for the most recent study period (2017–2023), as this period reflects current clinical practice. Adjustment for maternal age, BMI, and parity was performed using a logistic regression model to account for potential confounding, particularly given their increasing proportion over time. All statistical analyses were performed using IBM SPSS Statistics version 29.0.1.0.

3. RESULTS

A total of 1 018 972 deliveries occurred in Finland during the study period 2005–2023. The study population included 880 478 deliveries, accounting for 86.4% of all deliveries (Figure 1). The total births decreased by 26 891 births (7.6%), and the IOL rate doubled between the first and last study periods (from 18.2% to 35.7%).

3.1. Trends in baseline characteristics

The proportions of women aged ≥35 years and women with a BMI ≥30 kg/m² increased significantly during the study period, reaching 24% and 17%, respectively, in the last study period. Similar increasing trends were observed in the IOL group, although proportions were consistently higher. Meanwhile, smoking during pregnancy decreased in both the total study cohort and the IOL group.

The proportion of primiparas and women with a previous cesarean section remained stable in the total study cohort. Pregestational diabetes increased modestly (RR 1.5), whereas pregestational hypertension decreased slightly (RR 0.7) in the total study cohort. In the IOL group, primiparity, previous cesarean section, and pregestational diabetes were consistently more common and remained stable over time. Pregestational hypertension also decreased in the IOL group (Tables 1 and 2; Figure 2).

TABLE 1.

Maternal characteristics and pregnancy complications in the total study cohort across three study periods (2005–2023) and temporal trends (2017–2023 vs. 2005–2010).

Maternal characteristics, gestational age at birth, and pregnancy complications	2005–2010, % (95% CI)	2011–2016, % (95% CI)	2017–2023, % (95% CI)	RR 2017–2023 vs. 2005–2010 (95% CI)
Number of births (n)	303 867	295 988	280 623
Induced labor	18.2 (18.0–18.3)	23.6 (23.4–23.7)	35.7 (35.6–35.9)	1.97 (1.95–1.99)
Maternal age in years (M ± SD)	29.37 ± 5.35	29.79 ± 5.28	30.68 ± 5.22
Women ≥35 years	17.4 (17.3–17.5)	19.1 (19.0–19.3)	23.7 (23.5–23.8)	1.36 (1.35–1.38)
Women aged ≥40 years	3.3 (3.3–3.4)	3.4 (3.3–3.5)	4.6 (4.6–4.7)	1.39 (1.36–1.43)
BMI (Md, Q1–Q3)	23.1 (17.8–28.3)	23.3 (17.8–28.8)	24.2 (18.0–30.3)
BMI ≥30 kg/m2	11.0 (10.9–11.1)	12.6 (12.5–12.7)	16.8 (16.7–16.9)	1.53 (1.51–1.55)
Primipara	41.9 (41.8–42.1)	40.9 (40.8–41.1)	42.3 (42.1–42.5)	1.01 (1.00–1.01)
Previous cesarean section	8.0 (7.9–8.1)	8.6 (8.5–8.7)	8.1 (8.0–8.2)	1.02 (1.00–1.03)
Smoking at some point during pregnancy a	15.2 (15.1–15.3)	15.4 (15.3–15.5)	9.3 (9.2–9.4)	0.61 (0.60–0.62)
Anemia b	2.2 (2.1–2.2)	3.7 (3.6–3.8)	3.8 (3.7–3.9)	1.75 (1.70–1.81)
Pregestational diabetes	0.38 (0.36–0.41)	0.46 (0.44–0.49)	0.58 (0.55–0.61)	1.51 (1.40–1.63)
Pregestational hypertension	1.02 (0.98–1.05)	0.65 (0.62–0.68)	0.73 (0.70–0.76)	0.72 (0.68–0.76)
Early‐term (37+0–38+6 gw)	16.2 (16.1–16.3)	17.0 (16.8–17.1)	17.9 (17.8–18.1)	1.11 (1.10–1.12)
Full‐term (39+0–40+6 gw)	56.5 (56.3–56.6)	56.8 (56.6–57.0)	57.1 (56.9–57.3)	1.01 (1.01–1.02)
Late‐term (41+0–41+6 gw)	21.6 (21.5–21.8)	21.5 (21.4–21.7)	22.4 (22.2–22.5)	1.04 (1.03–1.05)
Post‐term (≥42+0 gw)	5.8 (5.7–5.8)	4.8 (4.7–4.8)	2.6 (2.6–2.7)	0.45 (0.44–0.47)
Gestational diabetes	10.9 (10.8–11.0)	16.0 (15.8–16.1)	22.0 (21.8–22.1)	2.01 (1.99–2.03)
Hypertensive disorders of pregnancy	5.2 (5.1–5.3)	4.7 (4.6–4.8)	6.0 (5.9–6.1)	1.16 (1.14–1.19)
Gestational hypertension	2.9 (2.9–3.0)	2.6 (2.5–2.6)	3.5 (3.4–3.5)	1.18 (1.14–1.21)
Preeclampsia	1.75 (1.70–1.80)	1.85 (1.80–1.90)	2.3 (2.3–2.4)	1.32 (1.28–1.37)
Intrahepatic cholestasis of pregnancy	0.91 (0.87–0.94)	1.06 (1.02–1.10)	1.34 (1.29–1.38)	1.47 (1.40–1.54)
Suspected placental insufficiency	2.9 (2.9–3.0)	3.9 (3.8–3.9)	5.5 (5.4–5.5)	1.86 (1.82–1.92)
SGA	1.31 (1.27–1.35)	1.88 (1.83–1.92)	2.6 (2.5–2.6)	1.95 (1.87–2.02)
LGA	1.39 (1.35–1.43)	2.1 (2.0–2.1)	3.8 (3.7–3.9)	2.73 (2.64–2.83)
PROM	1.79 (1.74–1.83)	4.7 (4.7–4.8)	8.8 (8.7–8.9)	4.94 (4.8–5.09)
Fear of childbirth	1.14 (1.10–1.18)	3.3 (3.2–3.3)	8.1 (8.0–8.2)	7.12 (6.86–7.36)
Other pregnancy‐related problems c	1.14 (1.10–1.18)	1.90 (1.85–1.95)	4.7 (4.6–4.8)	4.09 (3.94–4.24)

Note: The risk ratio (RR) compares the proportion of pregnancies with the outcome between the periods 2017–2023 and 2005–2010. An RR >1 indicates a higher risk in 2017–2023 compared with 2005–2010.

Abbreviations: BMI, body mass index (calculated using height and pre‐pregnancy weight or the weight in early pregnancy; available comprehensively after 2006); CI, confidence interval; LGA, suspected large for gestational age during pregnancy (estimated weight >2 SD based on ultrasonography result or registered as a birth diagnosis); M, mean; Md, median; PROM, prelabor rupture of membranes; Q1–Q3, interquartile range; SD, standard deviation; SGA, suspected small for gestational age during pregnancy (estimated weight <2 SD based on ultrasonography result or registered as a birth diagnosis).

^a Smoking at some point during pregnancy information is missing. Sample sizes are smaller.

^b Hemoglobin level <100 g/L.

^c Psychosocial problems/fatigue/symphyseolysis.

TABLE 2.

Maternal characteristics, and pregnancy complications in induced deliveries across three study periods (2005–2023), temporal trends (2017–2023 vs. 2005–2010), and odds ratios for induction of labor in the first and last study periods (2005–2010, 2017–2023) and adjusted odds ratios in 2017–2023.

Maternal characteristics, gestational age at birth, and pregnancy complications	2005–2010, % (95% CI)	2011–2016, % (95% CI)	2017–2023, % (95% CI)	RR 2017–2023 vs. 2005–2010 (95% CI)	OR 2005–2010 (95% CI)	OR 2017–2023 (95% CI)	aOR 2017–2023 (95% CI)
Number of births (n)	55 244	69 736	100 297
Age ≥35 years	21.0 (20.6–21.3)	22.6 (22.2–22.9)	26.8 (26.5–27.1)	1.28 (1.25–1.30)	1.34 (1.31–1.37)	1.31 (1.28–1.33)	1.40 (1.37–1.42)
Age ≥40 years	4.6 (4.4–4.8)	4.9 (4.7–5.0)	6.6 (6.4–6.7)	1.43 (1.37–1.50)	1.55 (1.48–1.62)	1.90 (1.83–1.96)
BMI ≥30 kg/m2	18.3 (18.0–18.6)	20.5 (20.2–20.8)	25.1 (24.8–25.4)	1.37 (1.34–1.40)	2.18 (2.12–2.24)	2.43 (2.38–2.48)	2.48 (2.43–2.53)
Primipara	43.7 (43.5–44.0)	45.2 (44.8–45.5)	45.7 (45.5–46.0)	1.05 (1.03–1.06)	1.10 (1.08–1.12)	1.25 (1.23–1.27)	1.36 (1.34–1.38)
Previous cesarean section	9.9 (9.5–10.4)	11.0 (10.8–11.2)	10.0 (9.3–10.6)	1.00 (0.97–1.03)	1.35 (1.31–1.40)	1.45 (1.41–1.49)	1.57 (1.52–1.62)
Anemia a	2.5 (2.4–2.7)	4.6 (4.4–4.7)	4.1 (4.0–4.1)	1.60 (1.50–1.70)	1.23 (1.13–1.35)	1.13 (1.08–1.17)	1.15 (1.11–1.20)
Smoking at some point during pregnancy b	16.0 (15.8–16.3)	16.9 (16.6–17.2)	10.8 (10.5–11.1)	0.67 (0.66–0.69)	1.08 (1.05–1.10)	1.33 (1.29–1.36)	1.26 (1.23–1.30)
Pregestational diabetes	1.21 (1.05–1.38)	1.30 (1.21–1.38)	1.29 (1.22–1.36)	1.07 (0.97–1.17)	6.07 (5.40–6.81)	6.93 (6.15–7.81)	4.15 (4.37–4.61)
Pregestational hypertension	2.5 (2.4–2.7)	1.54 (1.45–1.63)	1.55 (1.47–1.63)	0.61 (0.57–0.66)	3.79 (3.53–4.07)	5.79 (5.23–6.41)	6.00 (5.30–6.79)
Early‐term (37+0–38+6 gw)	20.1 (19.8–20.4)	22.6 (22.3–22.9)	22.6 (22.5–22.7)	1.12 (1.10–1.15)	2.00 (1.95–2.05)	2.11 (2.07–2.15)	2.07 (2.02–2.11)
Full‐term (39+0–40+6 gw)	39.6 (39.3–40.0)	41.3 (40.9–41.7)	44.7 (44.4–44.9)	1.13 (1.11–1.14)
Late‐term (41+0–41+6 gw)	21.4 (21.1–21.7)	21.9 (21.6–22.2)	26.4 (26.1–26.8)	1.23 (1.21–1.26)	1.50 (1.46–1.54)	1.88 (1.84–1.92)	1.90 (1.86–1.94)
Post‐term (≥42+0 gw)	17.9 (17.4–18.5)	14.2 (13.9–14.5)	6.3 (6.1–6.6)	0.34 (0.33–0.35)	9.99 (9.67–10.33)	16.85 (15.74–18.05)	16.86 (15.71–18.09)
Gestational diabetes	18.3 (18.0–18.6)	24.3 (24.0–24.6)	30.7 (30.5–31.0)	1.68 (1.65–1.71)	2.20 (2.14–2.25)	2.15 (2.12–2.19)	1.79 (1.75–1.82)
Hypertensive disorders of pregnancy	13.9 (13.6–14.2)	12.0 (11.7–12.2)	12.4 (12.2–12.6)	0.89 (0.87–0.91)	4.85 (4.69–5.01)	5.54 (5.35–5.74)	4.70 (4.53–4.87)
Gestational hypertension	7.6 (7.4–7.8)	6.4 (6.2–6.6)	7.2 (7.0–7.3)	0.95 (0.91–0.98)	4.23 (4.06–4.42)	5.51 (5.26–5.77)	4.61 (4.39–4.83)
Preeclampsia	5.7 (5.5–5.9)	5.1 (4.9–5.2)	4.9 (4.7–5.0)	0.86 (0.82–0.90)	6.84 (6.47–7.24)	5.66 (5.35–5.99)	5.12 (4.83–5.43)
Intrahepatic cholestasis of pregnancy	3.1 (2.9–3.2)	3.2 (3.0–3.3)	3.0 (2.9–3.1)	0.97 (0.92–1.03)	7.42 (6.87–8.01)	7.39 (6.81–8.00)	7.71 (7.10–8.37)
Suspected placental insufficiency	7.2 (7.0–7.4)	8.8 (8.5–9.0)	10.5 (10.3–10.6)	1.46 (1.41–1.51)	3.83 (3.67–4.00)	4.25 (4.10–4.40)	4.33 (4.18–4.49)
SGA	2.00 (1.88–2.12)	2.7 (2.5–2.8)	3.8 (3.7–3.9)	1.90 (1.78–2.03)	2.60 (2.41–2.80)	3.44 (3.25–3.63)	3.61 (3.41–3.81)
LGA	3.0 (2.9–3.2)	3.8 (3.6–3.9)	7.0 (6.8–7.1)	2.29 (2.17–2.41)	6.23 (5.79–6.71)	7.71 (7.31–8.13)	6.87 (6.50–7.25)
PROM	3.5 (3.4–3.7)	9.5 (9.3–9.7)	13.7 (13.5–13.9)	3.87 (3.69–4.05)	2.58 (2.44–2.73)	2.42 (2.36–2.48)	2.34 (2.28–2.41)
Fear of childbirth	1.76 (1.65–1.87)	4.8 (4.6–4.9)	10.4 (10.2–10.6)	5.90 (5.53–6.29)	1.78 (1.65–1.91)	1.58 (1.54–1.63)	1.57 (1.53–1.62)
Other pregnancy‐related problems c	2.2 (2.1–2.3)	3.8 (3.6–3.9)	7.6 (7.4–7.8)	3.44 (3.24–3.65)	2.48 (2.32–2.66)	2.63 (2.54–2.72)	2.54 (2.44–2.63)

Note: The risk ratio (RR) compares the proportion of pregnancies with the outcome between the periods 2017–2023 and 2005–2010. An RR >1 indicates a higher risk in 2017–2023 compared with 2005–2010. Odds ratios (ORs) compare the odds of induction of labor (IOL) in women with each risk factor vs. those without it, calculated separately for the first (2005–2010) and the last (2017–2023) study periods. Adjusted analyses were performed for the last period (2017–2023) only. Each variable was entered into a logistic regression model in turn, with maternal age, BMI, and parity included as covariates. Model estimates for maternal age, BMI and parity are therefore from one model, with only these three variables included. In the case of gestational weeks, full term was a reference group.

Abbreviations: BMI, body mass index (calculated using height and pre‐pregnancy weight or the weight in early pregnancy; available comprehensively after 2006); CI, confidence interval; IOL, induction of labor; LGA, suspected large for gestational age during pregnancy (estimated weight >2 SD based on ultrasonography result or registered as a birth diagnosis); PROM, prelabor rupture of membranes; SGA, suspected small for gestational age during pregnancy (estimated weight <2 SD based on ultrasonography result or registered as a birth diagnosis).

^a Hemoglobin level <100 g/L.

^b Smoking at some point during pregnancy is missing. Sample sizes are smaller.

^c Psychosocial problems/fatigue/symphyseolysis.

FIGURE 2.

Prevalence of maternal characteristics in the total study cohort and induction of labor group, 2005–2023.

3.2. Trends in pregnancy complications and other pregnancy‐related problems

The most prominent increase was observed in GDM, with its proportion doubling from 11% to 22% in the total study cohort. A similar increase was observed in the IOL group, where the proportion was consistently higher, reaching 31% in the last study period (RR 1.7).

The proportion of hypertensive disorders increased slightly (RR 1.2) in the total study cohort whereas it decreased slightly (RR 0.9) in the IOL group. Despite this decrease, the proportion in the IOL group remained approximately twofold higher than in the total study cohort, still at 12.4%.

Among fetal growth disturbances, the proportion of pregnancies with suspected placental insufficiency, LGA, and SGA increased modestly in the total study cohort. In the IOL group, absolute increases were slightly greater, although relative increases (RRs) were smaller than in the total study cohort. Within the IOL group, the largest relative increase was observed for LGA (RR 2.3). However, due to a higher baseline prevalence of suspected placental insufficiency, its absolute increase was more pronounced, reaching 10.5% in the last study period. The pattern for SGA mirrored that of placental insufficiency at lower levels. Overall, the proportion of fetal growth disturbances was nearly twice as high in the IOL group as in the total study cohort in the last study period.

Across all outcomes examined, the largest increases in risk were observed for PROM (RR 4.9), fear of childbirth (RR 7.1), and other pregnancy‐related problems (RR 4.1) in the total study cohort. Similar increasing trends were observed in the IOL group, with consistently higher risks across outcomes.

During the last study period, the most common pregnancy complications in the total study cohort were gestational diabetes (22%), PROM (9%), fear of childbirth (8%), hypertensive disorders (6%), and suspected placental insufficiency (5%). A similar distribution of complications was observed in the IOL group, although proportions were consistently higher (Tables 1 and 2; Figure 3).

FIGURE 3.

Prevalence of pregnancy complications in the total study cohort and induction of labor group, 2005–2023.

3.3. Odds ratios for IOL

In the last study period, pregestational diabetes (OR 6.9), pregestational hypertension (OR 5.8), and BMI ≥30 kg/m² (OR 2.4) were the baseline characteristics most strongly associated with IOL. Among pregnancy complications, the strongest associations with IOL were observed for LGA (OR 7.7), intrahepatic cholestasis (OR 7.4), hypertensive disorders (OR 5.5), suspected placental insufficiency (OR 4.3), and SGA (OR 3.4). The OR for IOL among women with GDM was 2.2. After adjustment for age, BMI, and parity, all examined maternal characteristics, pregnancy complications, and other pregnancy‐related problems remained statistically significant (Table 2).

The ORs for IOL increased over time in pregnancies with pregestational hypertension, LGA, SGA, hypertensive disorders, and suspected placental insufficiency. Meanwhile, the ORs remained rather stable for maternal age ≥ 35 years, BMI ≥30 kg/m², GDM, intrahepatic cholestasis, PROM, fear of childbirth, and other pregnancy‐related problems (Table 2).

3.4. Gestational age at delivery

In the total study cohort, most deliveries occurred full term throughout the study period, whereas the proportion of post‐term pregnancies decreased by half from the first to the last study period (Table 1).

The findings were similar in the IOL group, with most deliveries occurring full term; however, the decline in post‐term pregnancies was more pronounced. Furthermore, gestational age at birth shifted from post‐term to late‐ and full term. Post‐term pregnancy was strongly associated with IOL (OR 16.9) in the last study period, with the OR nearly doubling from the first to the last study period (Table 2; Figure 4).

FIGURE 4.

Gestational age distribution in the total study cohort and induction of labor group, 2005–2023.

4. DISCUSSION

The IOL rate in Finland doubled during 2005–2023. The most clinically meaningful increases in prevalence within the IOL group occurred among women with BMI ≥30 kg/m², maternal age ≥ 35 years, and gestational diabetes, reflecting their high baseline prevalence and overall contribution to IOL. The prevalence of suspected LGA doubled and was strongly associated with IOL in the last study period. In the IOL group, the prevalences of pregestational diabetes remained stable, pregestational hypertension decreased, whereas the prevalence of placental insufficiency increased. PROM and fear of childbirth showed the largest relative increases in prevalence, whereas post‐term pregnancy decreased the most.

The remarkable increases in the numbers of pregnant women with advanced age and obesity are a well‐recognized phenomenon worldwide and in other IOL studies. ⁷ , ⁸ , ⁹ , ¹⁰ , ¹⁷ , ¹⁹ The simultaneously increasing prevalence of pregnancy complications in our study has also been found in other studies. ⁸ , ⁹ , ¹⁰ , ¹³ , ¹⁴ , ¹⁵ , ²³ , ³¹

The increasing prevalence of maternal obesity and advanced age most likely explain the increase in the prevalence of GDM in our study. In Finland, most women undergo GDM screening, which increases its prevalence compared with risk factor‐based screening. The high prevalence of GDM in the IOL group reflects national guidelines, which recommend inducing labor in women with pharmacologically managed GDM by the due date, and earlier in cases of suspected macrosomia, regardless of treatment modality. In women with diet‐controlled GDM, labor should be induced no later than at 41⁺⁵ gw. Diet‐controlled GDM accounts for most cases of GDM. ²⁷ , ²⁸ , ²⁹ Our results suggest that many women with GDM undergo IOL without suspected LGA, as the prevalence of LGA was markedly lower than that of GDM. However, LGA was one of the strongest factors associated with IOL. The increasing prevalence of GDM, together with updated national management guidelines introduced in 2008, may partly explain the observed rise in full‐ and late‐term inductions.

Advanced maternal age, obesity, and pregestational conditions such as diabetes and chronic hypertension are established risk factors for fetal growth abnormalities, including placental insufficiency and SGA, which may partly explain the increasing prevalence of these conditions in the total study cohort. During the study period, the prevalence of pregestational diabetes modestly increased, whereas pregestational hypertension slightly decreased. In parallel, the prevalence of pregnancy complications, including GDM and all hypertensive disorders, increased. These conditions are also associated with placental insufficiency and SGA and may further contribute to the observed trends. In Finland, national recommendations for low‐dose acetylsalicylic acid prophylaxis to prevent preeclampsia and intrauterine growth restriction were introduced in 2021. ³⁰ This may have mitigated a sharper increase in hypertensive disorders and placental insufficiency during the last study period. Nevertheless, in the IOL group, hypertensive disorders and suspected placental insufficiency remained among the most common complications and were strongly associated with IOL. This is consistent with previous findings that active management reduces maternal morbidity compared with expectant management. ¹³ , ¹⁴ , ¹⁶ , ²¹ , ²² The decline in smoking during pregnancy may have attenuated a more pronounced increase in placental insufficiency.

The prevalence of PROM increased in both the total study cohort and the IOL group, with a more pronounced increase in the IOL group. This may reflect a shift in clinical practice toward more active induction. However, the OR for IOL among women with PROM remained stable throughout the study period. Improved diagnostic documentation may also have contributed to the observed increase. Furthermore, because this study was register‐based, we were unable to determine the timing of PROM in relation to induction, and some inductions may have been performed for other indications.

The prevalence of fear of childbirth increased markedly in both the total study cohort and the IOL group and became approximately as common as hypertensive disorders and placental insufficiency in the IOL group. However, the OR for IOL associated with fear of childbirth remained comparable between the first and last study periods. The increasing prevalence may reflect a general rise in fear of childbirth as well as more active detection and treatment during pregnancy, as reported in previous studies. ³¹ This interpretation is supported by the similarly steep increase observed in the total study cohort. IOL may enhance women's sense of control by allowing the timing of birth to be scheduled and a delivery plan to be established and may also serve as an alternative to elective cesarean section. Nevertheless, compared with spontaneous onset of labor, IOL carries a risk of worsening the childbirth experience if it results in an operative delivery. ²⁴ , ³² , ³³ , ³⁴

The prevalence of pregnancy‐related problems increased over the study period in both the total study cohort and the IOL group but remained consistently higher in the IOL group. Similar to fear of childbirth, the OR for IOL associated with these conditions did not increase during the study period. This pattern may reflect changes in diagnostic practices or broader societal trends. ³³ , ³⁴ , ³⁵

Intrahepatic cholestasis was strongly associated with IOL, although its overall prevalence remained low and largely stable. This aligns with previous reports indicating that its prevalence and clinical management have not changed substantially in recent years. ³⁶

The prevalence of post‐term pregnancies decreased in both the total study cohort and the IOL group, with a corresponding increase in late‐term deliveries, particularly in the IOL group. These trends likely reflect changes in clinical practice toward inducing labor before post‐term gestation to prevent stillbirth, supported by recent large‐scale randomized trials such as SWEPIS ³⁷ and INDEX. ³⁸ The prevalence of early‐term deliveries increased over the study period in both the total study cohort and the IOL group. A similar shift toward earlier gestational ages has been reported in previous population‐based studies and may reflect more proactive management aimed at preventing complications such as hypertensive disorders, diabetes, or placental insufficiency. This shift may also partly reflect increasing rates of elective induction without a clear medical indication. ⁷ , ⁸ , ⁹ , ¹⁰ Previous studies have suggested a higher risk of adverse neonatal outcomes among early‐term births compared with those at 39 gw. ³⁹ , ⁴⁰ However, assessment of neonatal outcomes was beyond the scope of the present study and will be addressed in future work.

This registry‐based study has several limitations. Its observational, retrospective design allows the identification of associations but not causal relationships. Because some women may have had multiple diagnoses, it was not possible to determine which diagnosis had the greatest influence on the decision to induce labor. This reflects clinical practice, where induction is often based on several coexisting indications, and some commonly recorded diagnoses may not be the actual reason for initiating IOL. Thus, overrepresentation of certain diagnoses as reasons for induction cannot be ruled out. In addition, we were unable to calculate the proportion of elective inductions, as the register does not include this information. The data may also contain inaccuracies in diagnostic coding due to human error. Nevertheless, the validity of the MBR has been demonstrated, and the quality and completeness of its data are considered good. ²⁶

This study has several strengths, including its large study population, nationwide coverage, and long study period, which also enabled the examination of rare pregnancy complications. The overall rate of missing data was low. Because the MBR includes all births in Finland, selection bias is minimized, and the results are likely reliable at the national level. Nevertheless, some variation in clinical practices may exist between hospitals. In addition, maternity clinic visits are free of charge, and outpatient and inpatient care are partially reimbursed in Finland, which promotes equitable access to care and reduces the influence of socioeconomic status on treatment.

5. CONCLUSION

The doubling of the IOL rate in Finland between 2005 and 2023 was accompanied by a shift toward a higher‐risk maternal population, characterized by increasing proportions of women of advanced maternal age, obesity, and GDM. Higher IOL rates among women with common pregnancy complications, including post‐term pregnancy, likely reflect increasing adherence to more active pregnancy management. Together, these findings suggest that the rise in IOL is driven by both changing maternal risk profiles and evolving clinical practice.

AUTHOR CONTRIBUTIONS

This study is part of the PhD research project of Vilja Vihtonen. Docent Kati Tihtonen and Vilja Vihtonen conceptualized the study and contributed to data acquisition. Vilja Vihtonen and Statistician MSc Mika Helminen organized the data and performed the statistical analyses. All authors contributed substantially to the interpretation of the results, critical revision of the manuscript, and its writing.

FUNDING INFORMATION

Financial support was provided by the Eka‐apuraha grant from the Finnish Medical Society Duodecim, awarded on October 10, 2024 (2500€).

CONFLICT OF INTEREST STATEMENT

The authors declare no competing interests.

ETHICS STATEMENT

This study was conducted using deidentified registry data and did not involve direct patient contact. The study was approved by the Findata—Social and Health Data Permit Authority in Finland on July 3, 2024 (THL/2389/14.02.00/2024 FD: 0988000376).

Supporting information

Table S1.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from Finnish Institute for Health and Welfare (THL). Restrictions apply to the availability of these data, which were used under license for this study. Data are available from the author(s) with the permission of Finnish Institute for Health and Welfare (THL).