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Table 1 Main characteristics of included studies

From: Inter-pregnancy interval and risk of recurrent pre-eclampsia: systematic review and meta-analysis

Study Country Study design Sample size (women with PE in 1st pregnancy) Definition of inter-pregnancy interval Inter-pregnancy interval studied (years) Elegibility criteria in pregnancy 1 Outcome in pregnancy 2 Definition of outcome Confounders used in the adjustment
Basso 2001 Denmark Retrospective cohort 8401 Interval between birth of the first child and conception date of the second one ≤1, 1–2, 2-3, 3–4, 4-5, 5–7, > 7. Danish women with PE that delivered at the hospital, with a 28 weeks or more single pregnancy and whose children were not given in adoption who had subsequently given birth PE or E ICD-9 and ICD-10 Maternal age in the second pregnancy, SES in the first pregnancy and change of SES between the first and second pregnancies.
Mostello USA Retrospective cohort 17,773 Interval between birth of the first child and conception date of the second one ≤1, 1–2, 2-3, 3–4, 4-5, 5–6, 6-7, 7–8, > 8. Women who delivered their first 2 singleton pregnancies at > 20 weeks gestation PE or E PE = HT + proteinuria or edema that is generalized and overt maternal age, prepregnancy BMI, smoking and SES
E = PE + convulsion, coma or both
Trogstad Norway Retrospective cohort 19,970 Time between the dates of the two deliveries ≤1, 1–5, 6-10, 11-15, > 15 All women with a first and second singleton pregnancy delivery after 16 weeks gestation in Norway PE or E BP > 140/90 after 20 week gestation combined with proteinuria ≥0.3 g/24 h (≥ + 1 dipstick) on at least two occasions. ICD-8 maternal age in 2nd pregnancy, new father, year of second delivery.
Hernandez Diaz Sweden Retrospective cohort 31,417 Difference between dates of last menstrual period <2, 2-4, 4-6, 6-8, > 8 Women who had their first delivery on or after 1 January 1987, with reproductive history followed until the end of 2004. PE or E ICD-9 and ICD-10 None
  1. References: PE pre-eclampsia, HT hypertension, E Eclampsia, ICD International Classification of Disease, SES Socioeconomic status