Table 2.
Risk factors tested for association with severe maternal morbidity
| 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 | ||||
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