ObjectivesThe aim of this study was to assess the prevalence and risk of pre-eclampsia and gestational hypertension in twin pregnancies compared with singleton pregnancies.DesignPopulation-based cohort study.SettingMedical Birth Registry of Norway and Statistics Norway.Participants929 963 deliveries with 16 174 twin pregnancies in 1999–2014.MethodsPre-eclampsia prevalences in twin and singleton pregnancies were described in percentages. Multivariable regression analyses were performed to assess the risks of pre-eclampsia and gestational hypertension in twin pregnancies compared with those in singleton pregnancies, adjusted for previously known risk factors.Primary and secondary outcome measuresPrevalence and risk of pre-eclampsia and gestational hypertension.ResultsThe prevalence of pre-eclampsia in the study population was 3.7% (3.4% in singleton pregnancies, 11.8% in twin pregnancies (p=0.001)). The OR for pre-eclampsia in twin pregnancies was three to fourfold compared with singleton pregnancies (OR 3.78; 95% CI 3.59 to 3.96). After adjustment for known risk factors, twin pregnancy remained an independent risk factor for pre-eclampsia (adjusted OR 4.07; 95% CI 3.65 to 4.54). The prevalence of gestational hypertension was 1.7% in women with singleton pregnancies and 2.2% in those with twin pregnancies (OR 1.27; 95% CI 1.14 to 1.41). After adjustment for known risk factors, gestational hypertension was not significantly associated with twin pregnancy.ConclusionsThe risk of pre-eclampsia in twin pregnancies was three to fourfold compared with singleton pregnancies, regardless of maternal age, parity, educational level, smoking, maternal comorbidity or in vitro fertilisation. The risk of gestational hypertension was not increased in women with twin pregnancies after adjustment for the main risk factors.

Prepregnancy BMI ≥30 was an independent risk factor for delivery by emergency cesarean section for both primiparous and parous women.

Objective To assess the association between preterm first birth and preterm second birth according to gestational age and to determine the role of placental disorder in recurrent preterm birth.Design Population-based registry study.Setting Medical Birth Registry of Norway and Statistics Norway.Population Women (n = 213 335) who gave birth to their first and second singleton child during 1999-2014 (total n = 426 670 births).Methods Multivariate logistic regression analyses, adjusted for placental disorders, maternal, obstetric and socio-economic factors.Main outcome measures Extremely preterm (<28 +0 weeks), very preterm (28 +0 -33 +6 weeks) and late preterm (34 +0 -36 +6 weeks) second birth.Results Preterm birth (<37 weeks) rates were 5.6% for first births and 3.7% for second births. Extremely preterm second births (0.2%) occurred most frequently among women with an extremely preterm first birth (aOR 12.90, 95% CI 7.47-22.29).Very preterm second births (0.7%) occurred most frequently after an extremely preterm birth (aOR 12.98,. Late preterm second births (2.8%) occurred most frequently after a previous very preterm birth (aOR 6.86,. Placental disorders contributed 30-40% of recurrent extremely and very preterm births and 10-20% of recurrent late preterm birth.Conclusion A previous preterm first birth was a major risk factor for a preterm second birth. The contribution of placental disorders was more pronounced for recurrent extremely and very preterm birth than for recurrent late preterm birth. Among women with any category of preterm first birth, more than one in six also had a preterm second birth (17.4%).

Objective: To assess the prevalence and risk of adverse perinatal outcomes in early-term (37 +0 -38 +6 weeks), full-term (39 +0 -40 +6 weeks), late-term (41 +0 -41 +6 weeks), and post-term (>42 +0 weeks) deliveries with spontaneous labor onset. Study design:A population-based cohort with data from the Medical Birth Registry Norway (MBRN) and Statistics Norway (SSB) was conducted. The study population consisted of 665,244 women with cephalic singleton live births at term or post-term with spontaneous labor onset during the period of 1999-2014 in Norway. Maternal, obstetric, and fetal characteristics were obtained from the MBRN. Maternal education data were obtained from the SSB. The prevalence rates of adverse perinatal outcomes for each gestational age (GA) group were estimated. Inter-group differences were detected with Chi square tests.Multivariable regression analysis adjusted for maternal age, educational level, smoking, parity, maternal diabetes, and preeclampsia was used to assess adverse outcome prevalence for early-late-, and post-term births compared to full-term births.Results Deliveries at early-term were associated with an increased prevalence of neonatal jaundice, polyhydramnios, small for gestational age (SGA) status, respiratory support, and neonatal intensive care unit (NICU) admission compared with deliveries at GAs of 39-43 weeks (p < 0.001). Low 5-min Apgar scores and newborn antibiotic treatment occurred at an increased prevalence in both early-term and post-term infants, relative to the full-term group (p < 0.001). The prevalence of oligohydramnios, meconium-stained amniotic fluid, and newborn birth injuries increased with increasing GA. Conclusions More perinatal morbidity was observed among early-term infants compared to infants with later term deliveries, underscoring the need for cautious management of low-risk early-term deliveries.