Laparoscopy guided Doppler ultrasound measurement of fetal blood flow indices during early to mid-gestation in pigs.

The objectives of this study were to obtain relevant blood flow indices of umbilical arteries (UmA) of porcine fetuses using a laparoscopic ultrasound probe and to relate these data with fetal size at early to mid gestation. Fetal parameters and flow indices, i.e., fetal length and area, fetal heart rate (FHR), systolic pulse duration (T1), interpulse duration (T2), T2/T1 ratio, peak systolic velocity (PSV), time averaged velocity (TAV), resistance index (RI) and pulsatility index (PI), were measured in 182 fetuses of 26 pregnant Landrace gilts on pregnancy day (PD) 36 (122 fetuses from 17 gilts), PD42 (19 fetuses from 3 gilts) and PD51 (42 fetuses from 6 gilts). Fetal heart rate was higher on PD36 than on PD42 (P<0.05). No differences (P>0.05) were obtained concerning systolic pulse duration, flow velocities and RI. On PD42, the PI was lower (P<0.05), while the interpulse duration (P=0.06) and T2/T1 ratio tended (P=0.08) to be higher on PD42 compared with PD36 and to PD51. To find differences in UmA blood flow parameters concerning fetal size, i.e., fetal length, fetuses were retrospectively grouped as follows: small (lower 25%), medium (mean 50%) and large (upper 25%), respectively. Although, fetuses differed in size (P<0.001) within and between days of pregnancy, FHR, PSV, TAV, RI and PI did not differ (P>0.05) among the size classes. Only systolic pulse duration tended to be longer (P=0.05) in large compared with small fetuses on PD36, and interpulse duration was lower in large fetuses on PD36 in comparison with PD51 (P<0.05). Though there was no link between fetal blood flow indices and fetal intrauterine growth retardation (IUGR), with further studies based on these flow indices, it might be possible to evaluate nutrient- or stress-related influences on fetal growth and development, particularly in the case of IUGR.