Preterm birth is the most important cause of neonatal death and morbidity. Defective cervical barrier is a major cause of preterm labour. This hypothesis was assessed immunologically by using flow cytometry to quantify leucocytes subpopulation in the cervix, morphologically by cervical length and volume as assessed by 3D ultrasound, and the cervical blood circulation was assessed by 3D ultrasound with power Doppler in patients at high risk of preterm labour. Immunologically, the most prevalent cervical leukocyte was the macrophage. Macrophages and the rest of leukocyte types in general were fewer in high risk patients than in normal pregnant controls. Morphologically, this study showed a significant association between cervical length and preterm labour, but not cervical volume. Also, there is increase in the vascularisation of the cervix in preterm labour patients. This book should be especially useful to Obstetricians, General Practitioners, young doctors, women in fertile age and researchers in the medical field.