with the concern of an abnormal karyotype indicate pubs; however, fetuses with a single umbilical artery may present a higher risk. in these cases, a single umbilical artery is required to perform the work of two arteries so it is often dilated up to one and a half times its size in order to meet these demands. a documented case of puncturing a single umbilical artery during pubs resulted in a decrease in the heart rate of the fetus with irregular improvement; however, it is difficult to conclude that these symptoms were solely the result of the punctured umbilical artery because these fetuses often have preexisting defects and abnormalities. while ultrasounds and color flow mapping can be used to avoid the umbilical artery and sample from the umbilical vein, the dilation makes the single umbilical artery easier to puncture. blood flow in the umbilical artery is seen to be twice the normal amount from about 20 weeks on so the effects of a punctured umbilical artery during pubs are more severe.