[Longitudinal reference intervals of maternal-fetal Doppler parameters]. 
To create longitudinal reference intervals for pulsatility index (PI) of the umbilical (UA), middle cerebral (MCA), uterine (UtA) arteries and ductus venosus (DV) in a Brazilian cohort.  A longitudinal observational study performed from February 2010 to May 2012.  Low risk pregnancies were scanned fortnightly from 18 to 40 weeks for the measurements of PI of the UA, MCA, DV and UtA. Linear mixed models were used for the elaboration of longitudinal reference intervals (5th, 50th and 95th percentiles) of these measurements.  PI obtained for the placental and abdominal portions of the umbilical artery were compared by the t-test for independent samples.  Two-sided p values of less than 0.05 were considered statistically significant.  A total of 164 patients underwent 1,242 scans.  There was significant decrease in PI values of all vessels studied with gestational age (GA).  From the 18(th) to the 40(th) week of pregnancy, the median PI values of UA (abdominal and placental ends of the cord), MCA, DV and the mean PI of the UtA ranged from 1.19 to 0.74, 1.33 to 0.78, 1.56 to 1.39, 0.58 to 0.41, and 0.98 to 0.66, respectively.  The following equations were obtained for the prediction of the medians: PI-UA=1.5602786 - (0.020623 x GA); Logarithm of the PI-MCA=0.8149111 - (0.004168 x GA) - [0.02543 x (GA - 28.7756)²]; Logarithm of the PI-DV=-0.26691- (0.015414 x GA); PI-UtA = 1.2362403 - (0.014392 x GA).  There was a significant difference between the PI-UA obtained at the abdominal and placental ends of the umbilical cord (p<0.001).  Longitudinal reference intervals for the main gestational Doppler parameters were obtained in a Brazilian cohort.  These intervals could be more adequate for the follow-up of maternal-fetal hemodynamic modifications in normal and abnormal pregnancies, a fact that still requires further validation.