Table 1.
Risk factors for preterm birth
| Risk factor | Clinical phenotype | Evidence level |
|---|---|---|
| Sociodemographic | ||
| Age27 | NA | NA |
| Maternal race15 | NA | NA |
| Paternal race28 | NA | NA |
| Maternal ethnicity29 | NA | NA |
| Paternal ethnicity28 | NA | NA |
| Education level30 | NA | NA |
| Household income31 | NA | NA |
| Employment status32,33 | NA | NA |
| Insurance status31 | NA | NA |
| Marital status30 | NA | NA |
| Body mass index15 | NA | NA |
| Clinical | ||
| Syphilis,34 hepatitis,35 gonorrhea,35 chlamydia,35 trichomonas,35 HSV,36 or GBS37 in current gestation | Infection/inflammation | Possible |
| Urinary tract infection or asymptomatic bacteriuria35 | Infection/inflammation | Possible |
| Kidney infection35 | Infection/inflammation | Possible |
| Pyelonephritis35 | Infection/inflammation | Possible |
| Chorioamnionitis35 | Infection/inflammation | Moderate |
| Vaginal bleeding35 | Decidual hemorrhage | Possible |
| Nonreassuring fetal heart tones, or fetal tachycardia35 | Decidual hemorrhage | Moderate (when together with vaginal bleeding) |
| Placenta previa35 | Decidual hemorrhage | Possible |
| Abruption35 | Decidual hemorrhage | Moderate |
| History of cervical conization procedure35 | Cervical insufficiency | Possible |
| History of loop electro-excision procedure35 | Cervical insufficiency | Possible |
| Short cervix15 | Cervical insufficiency | None to strong depending on measures |
| Funneling or hourglass membranes35 | Cervical insufficiency | Moderate (when together with short cervix) |
| Uterine fibroids35 | Uterine distension | Possible |
| Low amniotic fluid index35 | Placental dysfunction | Moderate |
| Preeclampsia or eclampsia15 | Placental dysfunction | Moderate for mild, strong for severe preeclampsia and eclampsia |
| Diabetes38 | Maternal comorbidities | Strong |
| Gestational diabetes in the current gestation39 | Maternal comorbidities | Moderate |
| Chronic hypertension40 | Maternal comorbidities | Strong |
| Cardiac,40a renal,35 autoimmune,41 pulmonary condition,35 anemia,42a or history of seizures35 | Maternal comorbidities | Moderate |
| Family history43 | Family history | None to strong depending on the degree of relatives and preterm delivery subtype |
| Stress, anxiety, or depression44 | Maternal stress | None to strong depending on survey responses |
| IUGR15a | Placental dysfunction | Moderate |
| Newly identified fetal anomalies45 | Placental dysfunction | Possible |
| Motor vehicle accident in current pregnancy35 | Decidual hemorrhage | Possible |
| Analytes | ||
| PAPP-A46,47a | Placental dysfunction | Possible when <0.52 MOM47 |
| hCG48a | Placental dysfunction | Possible when >50 mIU/mL48 |
| AFP49a | Placental dysfunction | Possible when >2.5 MOM50 |
| uEstriol51a | Placental dysfunction | Possible when >2.6 ng52 |
| Inhibin-A53a | Placental dysfunction | Possible when >2.25 MOM53 |
| Obstetric history | ||
| Number of previous deliveries54 | NA | NA |
| Number of previous abortions55 | NA | NA |
| Time since the last pregnancy16 | NA | NA |
| Previous birth weight56 | NA | NA |
| Previous caesarean section57 | NA | NA |
| Previous preeclampsia or gestational hypertension56a | Placental dysfunction | Possible |
| IUGR in previous pregnancy58a | Placental dysfunction | Possible |
| Previous oligohydramnios59a | Placental dysfunction | Possible |
| Maternal medical condition in previous pregnancy35a | Maternal comorbidities | Possible |
| Previous gestational diabetes60a | Maternal comorbidities | Possible |
| Previous placental abruption56a | Placental dysfunction | Possible |
Risk factors for preterm birth are listed in the first column. Clinical phenotype and the level of evidence that a risk factor provides for the phenotype are also presented where applicable. Phenotype mapping was done with the phenotyping tool derived from the study by Manuck et al35 and expanded in this work. NA in the clinical phenotype and evidence level columns corresponds to the risk factors that were not mapped to any phenotype and were themselves final variables included in the model.
AFP: alpha-fetoprotein; GSB: group B Streptococcus; hCG: human chorionic gonadotropin; HSV: herpes simplex virus; IUGR: intrauterine growth restriction; MOM: multiple of the median of normal pregnancies; PAPP-A: pregnancy-associated plasma protein A.
New risk factors added by the clinical expert.