الفهرس 
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Abstract
Preterm birth (PTB) is a complex obstetric syndrome and a major cause of neonatal morbidity and mortality. It occurs in approximately 5-18% of pregnancies and is a leading cause of antenatal hospitalization. It is defined as a delivery that occurs between 20 and 37 weeks of gestation. The causes of preterm birth are multifactorial and can be classified to spontaneous and iatrogenic causes.
70-80% of PTBs are spontaneous, due to preterm labor, preterm pre-labor rupture of membrane and rarely cervical insufficiency. The remaining 20-30% are iatrogenic including medical conditions affecting the mother or fetus (preeclampsia, placenta Previa, placental abruption, fetal growth restriction, etc.).
In association with preterm birth, neonatal mortality and morbidity such as respiratory distress syndrome (RDS), necrotizing entero-colitis, retinopathy of prematurity, intra-ventricular hemorrhage, and sepsis can occur.
Many screening methods are now done for diagnosis of preterm labor such as biological fluids (e.g., amniotic fluid, vaginal secretions, urine, cervical mucus, serum or plasma, or both, and saliva) that can be used to assess the value of biomarkers like metalloproteinase-9 which rises substantially about 24 hours before labor initiation, salivary estriol concentration predicts late preterm birth and fetal fibronectin glycoprotein which if present in cervico-vaginal fluid indicates chorio-decidual disruption.
So, accurate identification of women who are truly in preterm labor allows the appropriate application of interventions such as antenatal corticosteroid therapy, prophylaxis for group B streptococcal infection,magnesium sulphate for neuro-protection and transfer of the patient to a facility with an appropriate nursery level if necessary, which can all improve neonatal outcome, avoid unnecessary interventions and associated costs.
However, 30% of preterm labor (PTL) resolves spontaneously and 50% of women hospitalized for PTL actually give birth at term. Less than 10% of women give birth within seven days of presentation.
Therefore, an accurate diagnostic PTL test, which could identify and stratify women at risk of PTB have been proposed. Among these tests there are measurements of the cervical length (CL), cervico-vaginal placental alpha macroglobulin 1 testing, or a combination of both.
The cervix plays the key role in the process of labor progress. It is a biochemically active tissue that modifies its biomechanical qualities in a remodeling process during pregnancy to be prepared for delivery.
During pregnancy, the most important biological function of the cervix is to maintain the fetus within the uterus. Assessment of CL by ultrasound is one of the most studied parameters for early detection of PTL. It is determined as the linear distance between internal and external cervical os, excluding the endo-cervical funnel.
Transvaginal sonography (TVS) is currently the best modality for imaging the uterine cervix. It is simple, reproducible and non-expensive. It provides high-quality cervical images and enables assessment of CL and funneling presenting with threatened PTL.
Most data regarding this issue focused on CL measurements in the second trimester of pregnancy. Short cervix in the second trimester, detected by TVS was significantly associated with PTL and was found to be a strong predictor of this complication.