The human heart undergoes an alternating | function of Systole and Diastole to pump and | receive blood. Systole is a state in which tb I heart contracts to pump blood to various par.- I of the body. Diastole is a state of relaxations

which the heart receives pur Fed blood. This received blood is again pumps.. out thus following a continuous cycle. In th non-pregnant human female, the Wide orbs obtained at Doppler are characterized bv a high blood flow during systole and little or -o flow during diastole except in the block vessels of the brain and those that outflow rrom the heart.

During pregnancy; t2- - blc. d flow to the uterus increases tremen corn 50ml per ( essel returning blood from the baby  placenta for oxygen and, cleansing), the . scendinv aorta of the fQetus and the inie. carotid and cerebral vessels (vessels of to

brain) of the baby The Renal arteries (vessels of the kidney) are often studied for research purposes.

As mentioned before, Doppler ultrasound can be used to detect pregnancies at risk (for e.g. future development of blood pressure l

Archway emery             

Doppler waveforms from nonnal pregnancy. Shown clockwise are normal waveforms 1IGIII the mated al arcuate, uterine, and external iliac arouses. and from the fetal umbilical artery and decending aorta. Reversed enddiastolicflow velocit  is apparent in the external iliac artery, whereas contirlous diastolicflow characterizes the ulenlle and arcuate vessels. Fhall): note the greatly diminshed end diastolic fo:v in the fetal descending aorta.

minute shortly after conception to 500 to 750rnl per minute by the end of pregnancy. During pregnancy, the placenta has high volume blood flow and blood flows continuously throughout diastole in the blood vessels of the mother and baby which supply the placenta. Because of this constant increase of blood flow, the speed of the flow also increases with advancing pregnancy

The commonly studied blood vessels are the uterine artery (blood vessel supplying the uterus! in the mother, the Umbilical artery pregnancy) and future problems likely to occur in the foetus, for example Growth Restriction even before the deleterious condition becomes manifest. The sonologist will look at the flow in the uterine and umbilical arteries and any alternations in the flow of blood may represent resistance to flow of blood within the placenta. This screening is usually carried out at 18 and 24 weeks of pregnancy.