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Table 2 Risk factors tested for association with severe maternal morbidity

From: A scoping review of severe maternal morbidity: describing risk factors and methodological approaches to inform population-based surveillance

Potential covariates for use in risk adjustment Number of studies that used the variable in risk adjustment Number of studies with a statistically significant result Number of studies with a non-significant result Number of studies where statistical significance was not reported
Pre-existing clinical
 Heart disease: including CHF,a,b CHD,a,c pulmonary hypertension,a ischemic heart disease,a valvular heart disease,a conduction disorders 43 (53.1%) 10 0 33
 Sickle cell diseasea 11 (13.6%) 1 0 10
 Collagen vascular disease: including SLEa,d and rare autoimmune, rheumatoid arthritis and other collagen vascular 27 (33.3%) 5 0 22
 HIVa 21 (25.9%) 3 0 18
 Chronic renal diseasea 37 (45.7%) 7 0 30
 Chronic hypertensiona 68 (84.0%) 20 0 48
 Chronic diabetesa 67 (82.7%) 15 1 51
 Chronic lung disease, including asthmaa 31 (38.3%) 5 1 25
 Thyroid disease, hypothyroidism 8 (9.9%) 0 0 8
 Maternal soft tissue condition: includes other uterine surgery, fibroids, cervical conditions 5 (6.2%) 0 0 5
 Pelvis abnormal 1 (1.2%) 0 0 1
 Gynecological conditions: e.g., endometriosis, PCOS,e peritoneal adhesions 3 (3.7%) 0 0 3
 Skin and subcutaneous tissues 1 (1.2%) 0 0 1
 Hospitalization in prior 5 years or during pregnancy 4 (4.9%) 1 0 3
 Drug abuse:a including amphetamine, opioid, other; one vs multiple substance, cocaine, combination with alcohol or smoking or mental health conditions 27 (33.3%) 4 1 22
 Alcohol abusea 16 (19.8%) 1 1 14
 Smoking 34 (42.0%) 6 7 21
 Mental health, including depression 16 (19.8%) 4 0 12
 Obesity class, BMI,f weight gain during pregnancy 40 (49.4%) 15 5 20
 Height 2 (2.5%) 0 0 2
 Weight gain 3 (3.7%) 2 1 0
 Liver disorders, including failure, hepatitis B or C 11 (13.6%) 2 0 9
 Digestive diseases, including IBDg 9 (11.1%) 1 2 6
 Seizures and other CNSh conditions, e.g., stroke, MSi 12 (14.8%) 2 0 10
 Blood diseases: including thrombocytopenia, coagulopathy, or anaemia 16 (19.8%) 3 0 13
 Fluid electrolyte disorders 2 (2.5%) 0 0 2
 Paralysis 2 (2.5%) 0 0 2
 Peripheral vascular disorders 4 (4.9%) 0 0 4
 Weight loss 2 (2.5%) 0 0 2
 Musculoskeletal conditions 5 (6.2%) 0 2 3
 Malignancy 4 (4.9%) 0 0 4
 History of organ transplant 1 (1.2%) 0 0 1
 High risk summary measure 28 (34.6%) 14 0 14
 VTE,j anticoagulant use (now or in past) 4 (4.9%) 1 0 3
 Hyperlipidemia 1 (1.2%) 0 0 1
 Disorders of the adrenal gland 1 (1.2%) 0 0 1
 Obstructive sleep apnea 1 (1.2%) 1 0 0
 Genital herpes 4 (4.9%) 0 0 4
 Cystic fibrosis 2 (2.5%) 0 1 1
 Maternal agea 79 (97.5%) 31 2 46
 Maternal race/ethnicity 44 (54.3%) 24 0 20
N = 41 pre-existing clinical covariates
Obstetrical Antepartum
  Parity (nulliparous vs grand multipara) and combinations with prior cesarean birth 48 (59.3%) 16 0 32
  Prior cesarean delivery,a number of prior cesareans 48 (59.3%) 13 2 33
  Prior preterm birth 4 (4.9%) 0 0 4
  Multiple gestationa 69 (85.2%) 15 2 52
  Preeclampsia:a including severe, mild, gestational, eclampsia 47 (58.0%) 13 1 33
  Placental conditions 25 (30.9%) 6 0 26
  Gestational diabetes 29 (35.8%) 4 5 20
  Assisted conception: invasive vs. non-invasive, IUI,k ovulation induction, IVF, ICSI,l diagnosed infertility, infertility treatment 13 (16.0%) 7 0 6
  Neonatal congenital anomalies or cancer 14 (17.3%) 0 0 14
  Fetal presentation 14 (17.3%) 2 2 10
  LGAm or SGAn fetus 14 (17.3%) 3 1 10
  Oligohydramnios/polyhydramnios 6 (7.4%) 1 0 5
  Male fetus 5 (6.2%) 0 0 5
  First trimester prenatal care, adequate prenatal care 17 (21.0%) 8 0 9
  Provider type (at PNC,o delivery) 4 (4.9%) 1 0 2
  Isoimmunization 4 (4.9%) 0 0 4
  Number of previous livebirths, number of previous miscarriages/previous miscarriage, ectopic, termination 4 (4.9%) 1 0 3
  Prior D&Cp 1 (1.2%) 0 0 1
  History of hemorrhage previous pregnancy 2 (2.5%) 2 0 0
  History of hypertensive disorder in a previous pregnancy 1 (1.2%) 1 0 0
  History of SGA 1 (1.2%) 0 0 1
  Group B streptococcus screen positive 1 (1.2%) 0 0 1
N = 22 obstetrical antepartum covariates
Intrapartum or postpartum
  Bishop score < 6 1 (1.2%) 1 0 0
  Unengaged fetal head 3 (3.7%) 0 0 3
  Uterine rupture, prolapsed cord 2 (2.5%) 0 0 3
  Hemorrhage 4 (4.9%) 1 0 3
  Prior stillbirth or infant death 4 (4.9%) 0 0 4
  Stillbirth 9 (11.1%) 0 0 9
  Route of delivery: includes labor y/n, operative VD,q cesarean 35 (43.2%) 12 3 20
  Maternal indication for cesarean 1 (1.2%) 0 0 1
  Cesarean incision type 1 (1.2%) 0 1 0
  Induction 12 (14.8%) 5 0 7
  Cervical ripening 1 (1.2%) 1 0 0
  Epidural use 3 (3.7%) 0 0 3
  PROM,r PPROMs 8 (9.9%) 0 0 8
  Chorioamnionitis or maternal infection 4 (4.9%) 1 0 3
  Birth day: weekend, night 6 (7.4%) 3 2 1
  Gestational age at delivery, preterm birth, type of preterm birth 33 (40.7%) 6 0 27
  Preterm birth spontaneous vs indicated 2 (2.5%) 0 0 2
  Labor anomalies: prolonged second stage, oxytocin 5 (6.2%) 1 0 4
  General vs neuraxial anesthesia 3 (3.7%) 2 0 1
  Perineal trauma 1 (1.2%) 0 0 1
  Elective delivery 6 (7.4%) 0 0 6
  Fetal distress not in labor (separate from elective) 1 (1.2%) 0 0 1
N = 22 intrapartum/postpartum covariates
Other patient-level covariates
  Year of childbirth 29 (35.8%) 13 2 14
  Income 2 (2.5%) 1 0 1
  Rural 4 (4.9%) 2 0 2
  Insurance 39 (48.1%) 16 4 19
  Education 21 (25.9%) 7 0 14
  SESt 5 (6.2%) 1 0 4
  Foreign born 16 (19.8%) 7 1 8
  Language spoken 1 (1.2%) 0 0 1
  Refugee status 1 (1.2%) 0 0 1
  Duration of residence 1 (1.2%) 0 0 1
  Working 2 (2.5%) 0 2 0
  Married 13 (16.0%) 3 2 8
  Profession 1 (1.2%) 0 0 1
  Home birth 1 (1.2%) 0 0 1
  Transfer in from other hospital 3 (3.7%) 0 0 3
N = 15 other patient-level covariates
Hospital-level covariates
  Hospital level of maternal care 2 (2.5%) 1 1 0
  Hospital size or delivery volume 17 (21.0%) 6 3 8
  Hospitalist 1 (1.2%) 0 1 0
  Hospital ownership 11 (13.6%) 4 2 5
  Hospital teaching 15 (18.5%) 5 2 8
  Hospital urban/rural 9 (11.1%) 2 2 5
  Hospital percent high-risk 1 (1.2%) 1 0 0
  Hospital percent non-White 1 (1.2%) 1 0 0
  Hospital black-serving 1 (1.2%) 1 0 0
  Hospital percent Medicaid 3 (3.7%) 1 0 2
  Hospital coding intensity 1 (1.2%) 1 0 0
  Hospital percent midwife births 1 (1.2%) 0 1 0
  NICUu level 4 (4.9%) 2 1 1
  Hospital cesarean rate general endotracheal anesthesia 1 (1.2%) 0 0 1
  Hospital epidural rate 1 (1.2%) 0 0 1
  Hospital induction rate 1 (1.2%) 0 0 1
  Hospital percent NTSVv 2 (2.5%) 0 0 2
  Hospital percent early elective deliveries 2 (2.5%) 0 0 2
  Hospital Clinical Processes of Care quintiles 1 (1.2%) 0 0 1
  Hospital Patient Perspectives of Care quintiles 1 (1.2%) 0 0 1
  Hospital number triaged per day 1 (1.2%) 0 0 1
  Hospital number triaged per delivery 1 (1.2%) 0 0 1
  Hospital > 4 hospitals within 20 miles of residence 1 (1.2%) 0 0 1
  Hospital excellent doctor:nurse relationship 1 (1.2%) 0 0 1
  Hospital doctors/1000 deliveries 1 (1.2%) 0 0 1
  Hospital MFMw on staff 1 (1.2%) 0 0 1
  Hospital midwives available 1 (1.2%) 0 0 1
  Hospital anesthesia available 24/7 1 (1.2%) 0 0 1
  Hospital anesthesia staff have no other responsibilities 1 (1.2%) 0 0 1
  Hospital equivalent staffing day and night 1 (1.2%) 0 0 1
  Hospital cesarean in main hospital operating room 1 (1.2%) 0 0 1
  Hospital radiology available 24/7 1 (1.2%) 0 0 1
  Hospital blood bank available24/7 1 (1.2%) 0 0 1
  Hospital massive transfusion protocol in place 1 (1.2%) 0 0 1
  Hospital pharmacist dedicated to L&Dx 1 (1.2%) 0 0 1
  Hospital Bakri Balloon available 1 (1.2%) 0 0 1
  Hospital epidural easy to get 1 (1.2%) 0 0 1
  Hospital adult critical care 24/7 1 (1.2%) 0 0 1
  Hospital subspecialty intensive care units available 1 (1.2%) 0 0 1
  Hospital difficult to get consults 1 (1.2%) 0 0 1
  Hospital has NICU 1 (1.2%) 0 0 1
  Hospital central FHRy monitoring 1 (1.2%) 0 0 1
  Hospital emergency response team available to L&D 1 (1.2%) 0 0 1
  Hospital allow TOLACz 1 (1.2%) 0 0 1
  Hospital 100% of cesareans begun within 30 min 1 (1.2%) 0 0 1
  Hospital intermittent FHR monitoring < 50% of patients 1 (1.2%) 0 0 1
  Hospital doctors sign out to each other 1 (1.2%) 0 0 1
  Hospital formal rounds are conducted on L&D 1 (1.2%) 0 0 1
  Hospital drills and simulations required 1 (1.2%) 0 0 1
  Hospital FHR monitoring course required of doctors 1 (1.2%) 0 0 1
  Hospital tracking of haemorrhage occurs 1 (1.2%) 0 0 1
  Hospital tracking of infection occurs 1 (1.2%) 0 0 1
  Hospital tracking of 3rd & 4th degree lacerations occurs 1 (1.2%) 0 0 1
  Hospital has cesarean evaluation team 1 (1.2%) 0 0 1
  Hospital allows maternal transfers in 1 (1.2%) 0 0 1
  Hospital has a protocol for induction of labor 1 (1.2%) 0 0 1
  Hospital has a protocol for cesarean delivery 1 (1.2%) 0 0 1
  Hospital gives education regarding induction of labor 1 (1.2%) 0 0 1
N = 58 hospital-level covariates
Community-level covariates
  Region 21 (25.9%) 6 1 14
  Neighborhood poverty 3 (3.7%) 0 2 1
  Miles from zip code to hospital 1 (1.2%) 0 1 0
  Geographic designation of area urban/rural 8 (9.9%) 2 0 6
  County frequency of obstetricians/anesthesiologists 1 (1.2%) 0 1 0
  County frequency of births to teens 1 (1.2%) 0 1 0
  County frequency of unmarried women 1 (1.2%) 0 1 0
  County frequency of divorced females 1 (1.2%) 0 1 0
  County frequency of female family heads 1 (1.2%) 0 1 0
  County frequency of females with no insurance 1 (1.2%) 0 1 0
  County frequency of foreign-born persons 1 (1.2%) 0 1 0
  County frequency of persons with less than high school education 1 (1.2%) 0 1 0
  County frequency of non-White persons 1 (1.2%) 0 1 0
  County household income measure 18 (22.2%) 4 2 12
  County frequency of unemployed persons 1 (1.2%) 0 1 0
 County frequency of food stamp beneficiaries 1 (1.2%) 0 1 0
  County frequency of persons with no phone 1 (1.2%) 0 1 0
  County frequency of households with > 1 person/room 1 (1.2%) 0 1 0
  County number of days with good air 1 (1.2%) 0 1 0
  County number of deaths due to AIDSaa 1 (1.2%) 0 1 0
  County number of deaths due to MVAbb 1 (1.2%) 0 1 0
  County death suicide 1 (1.2%) 0 1 0
N = 22 community-level covariates
TOTAL: N = 180 covariates
  1. aincluded in Bateman Comorbidity Index; bCHF congestive heart failure; cCHD congenital heart disease; dSLE systemic lupus erythematosus; ePCOS polycystic ovary syndrome; fBMI body mass index; gIBD inflammatory bowel disease; hCNS central nervous system; iMS multiple sclerosis; jVTE venous thromboembolism; kIUI intrauterine insemination; lICSI intracytoplasmic sperm injection; mLGA large for gestational age; nSGA small for gestational age; oPNC prenatal care; pD&C dilatation and curettage; qVD vaginal delivery; rPROM premature rupture of membranes; sPPROM preterm premature rupture of membranes; tSES socioeconomic status; uNICU neonatal intensive care unit; vNTSV nulliparous term singleton vertex; wMFM maternal fetal medicine specialist; xL&D labor and delivery area; yFHR fetal heart rate; zTOLAC trial of labor after cesarean; aaAIDS acquired immune deficiency syndrome; bbMVA motor vehicle accident