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The ductus venosus has a central role in the distribution of highly oxygenated umbilical venous blood to the heart. Its waveform is related to the pressurevolume changes in the cardiac atria and it is therefore important in the monitoring of any fetal condition that may affect forward cardiac function. The cardiovascular parameters that can influence forward cardiac function include afterload, myocardial performance and preload. Decreased forward flow during atrial systole (a-wave) is the most sensitive and ubiquitous finding when any of these parameters is affected. In contrast, decreased forward velocities during end-systolic relaxation (v-wave) are more specifically related to myocardial performance. The ductus venosus pulsatility index alone does not accurately reflect cardiac function, and in cases of suspected fetal cardiac dysfunction, echocardiography is required to identify the underlying mechanism. The role of ductus venosus Doppler in the assessment of fetal growth restriction, supraventricular tachycardia, fetal hydrops, complicated monochorionic twins and congenital heart disease is discussed with these considerations in mind.Abbreviations: AV, atrio-ventricular; CHD, congenital heart disease; DV, ductus venosus; FGR, fetal growth restriction; PIV, pulsatility index for veins; SVT, supraventricular tachycardia; TTTS, twin-to-twin transfusion syndrome. The central role of ductus venosus in fetal cardiovascular assessmentDoppler examination of the fetal venous circulation was introduced into perinatal medicine over 25 years ago to extend cardiovascular functional assessment beyond the capabilities of arterial Doppler. All central and precordial venous vessels share the same flow pattern of forward flow in ventricular systole and diastole and a temporary decrease in forward flow during end-ventricular systole and atrial systole. However, the ductus venosus (DV) has several important characteristics that favor its widespread use in fetal medicine. It is a short vessel with a relatively fixed position, allowing for standardization of the Key messageThe ductus venosus waveform reflects the pressurevolume changes in the heart. Despite the limited specificity of the ductus venosus waveform, its correlation with cardiac forward function makes it of central importance in assessing the overall severity of fetal cardiovascular pathology. Ductus venosus Doppler study has a critical role in directing the clinical management of fetuses at risk of cardiovascular deterioration.ª

Parer & Ikeda and NICHD classifications had the highest specificity in detecting umbilical cord arterial pH ≤7.15. The high specificity of the NICHD classification is hindered by a high percentage of "intermediate" traces (80%). Parer & Ikeda classification is the one that best classify as pathological only the traces of fetuses that are truly at risk of acidemia, thus avoiding unnecessary intervention. It also showed the best trade-off between sensitivity and specificity and the lowest rate of traces considered "intermediate."

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Following weight rehabilitation, the individual's metabolic set point before weight loss and the current insulin levels appear significant in predicting the reactivation of reproductive function.