Table 1.

Risk Factors preterm birth (PTB). Risk factors for PTB used for sample classification in low/high PTB risk and their definitions

Risk factors	Definition	Uterine environment	Study
Short Cervical Length	Transvaginal ultrasound cervical length ≤ 25 mm (2nd to 3rd centile)	U	[19]
Polyhydramnios Severe	Single deepest pocket (SDP) ≥ 16.0 cm or amniotic fluid index (AFI) > 35.0 cm	U	[20]
pPROM	Preterm prelabor rupture of membranes	U	[21]
Medically Assisted Procreation	All the methods or techniques based on the manipulation of reproductive cells (gametes) that will allow infertile couples to conceive a child	U	[22]
Prior PTB	Previous delivery that occurs between 20 and 37 weeks of gestation	U	[4]
Pregnancy Induced Hypertention (PIH)	Systolic blood pressure ≥ 140 mmHg or diastolic blood pressure ≥ 90 mmHg on at least 2 occasions at least 4 hours apart after 20 weeks of gestation in a previously normotensive patient	P	[23]
Placenta Previa	Placenta that completely or partially covered the internal os on a second- or third-trimester imaging study	P	[24]
Placental Abruption	Partial or complete placental detachment prior to delivery of the fetus	P	[5]
Preeclampsia, Eclampsia, HELLP	New onset of hypertension and proteinuria or hypertension and end-organ dysfunction with or without proteinuria after 20 weeks of gestation in a previously normotensive woman	P	[23]
Fetal Growth Restriction	EFW < 3 centile or EFW < 10 centile with Doppler abnormalities on maternal or fetal side or decline in EFW	F	[25]
Urinary Tract Infections (UTI)	Cystitis (infection of the bladder/lower urinary tract) and pyelonephritis (infection of the kidney/upper urinary tract) n pregnant women	E	[26]
Complex Autoimmune Diseases With Polytherapy	i.e. Systemic lupus erythematosus (LES), Antiphospholipid Syndrome (APS)	E	[27]