During progression of labor S/D of umbilical artery ratio?

Ans. b. DecreasesFeto-placental perfusion assessed with Doppler ultrasound by three methods. Systolic versus end diastolic flow velocity (S/D flow) in the umbilical vessels, middle cerebral artery, and ductus venosus.UMBILICAL ARTERY DOPPLERThis test measures the ratio of systolic and diastolic blood flow in the umbilical artery.The umbilical circulation normally has low resistance, so significant diastolic blood flow is expected.The systolic/diastolic (S/D) ratio normally decreases throughout pregnancy.Umbilical artery S/D ratio is gestational age-dependent.The S/D ratio normally decreases from approximately 4.0 at 20 weeks to 2.0 at term, and it is generally less than 3.0 after 30 weeks.Because of downstream impedance to flow, more end-diastolic flow is observed at the placental cord insertion than at the fetal ventral wall. Thus, abnormalities such as absent or reversed end-diastolic flow will appear first at the fetal cord insertion site.This test is predictive of poor perinatal outcome only in IUGR foetuses.Non-reassuring findings, which may indicate need for delivery, are absent diastolic flow and reversed diastolic flow.Note:-This notch disappears at 24 weeks of pregnancy as the resistance of uterine artery decreases due to trophoblastic invasion. There is no diastolic notch in late second and third trimester. But if this diastolic notch persists beyond 24 weeks, it predicts that female will have PIH during this pregnancy.Extra MileUmbilical artery Doppler waveform patterns vs USG patternsNORMAL UMBILICAL ARTERY DIASTOLIC FLOWABSENT UMBILICAL ARTERY DIASTOLIC FLOWREVERSED UMBILICAL ARTERY DIASTOLIC FLOW