Case reports of transient single umbilical artery blood flow in monochorionic twins.

We report two cases of transient single umbilical artery (UA) blood flow in growth-discordant monochorionic twins. The interval of single UA was for one week in case 1 and for a few days in case 2. We speculate a cord factor such as length, twisting, and insertion site can be the etiology of this condition.

Acceleration time of fetal arterial blood flow velocity waveforms: a preliminary study.

BACKGROUND: Doppler ultrasonography has been widely used for fetal estimation, but most of them were estimated by the resistance and pulsatility indices. Acceleration time is one of parameters of flow velocity waveforms, but only few reports had discussed acceleration time of fetal circulation. METHODS: We analyzed Doppler flow velocity waveforms of fetal middle cerebral artery, descending aorta and abdominal umbilical artery obtained from 70 normal pregnant women between 18 and 40 weeks. Acceleration time was cross-sectionaly examined throughout pregnancy course. RESULTS: The acceleration times revealed no remarkable changes throughout pregnancy course in the middle cerebral artery, but significant increases were observed in the acceleration time of the descending aorta between 18-23 and 24-32 weeks. It also significantly decreased after 33 weeks compared to that of 18-32 weeks in the umbilical artery. CONCLUSIONS: The acceleration time in fetal descending aorta is significantly shorter than that in the abdominal umbilical artery between 18 and 32 weeks of gestation. The umbilical arterial acceleration time apparently decreases throughout pregnancy course. Its values are almost double for that in the descending aorta between 18 and 23 weeks, but it becomes to be equal to the aortic acceleration time. The continuous decrease of the umbilical arterial acceleration time might be a result of a relative increase of placental flow.

Uterine artery flow velocity waveforms during uterine contractions: differences between oxytocin-induced contractions and spontaneous labor contractions.

AIM: To clarify the effects on uterine arterial flow velocity waveforms of uterine contractions following oxytocin infusion and during spontaneous labor. METHODS: Uterine arterial flow velocity waveforms were obtained by pulsed Doppler methods from 22 women during an oxytocin challenge test (OCT), 26 women during oxytocin-induced labor, and 40 women during spontaneous labor. Mean resistance index (RI) for bilateral arteries was used for analyses. After the onset of labor, flow velocity waveforms were assessed according to cervical dilatation. During OCT, Doppler flow velocimetry was performed when three uterine contractions occurred per 10-min period. RESULTS: RI values did not differ significantly between induced and spontaneous labor during relaxations at any level of cervical dilatation. However, during contractions, RI was significantly higher for induced labor than for spontaneous labor. Absence or reversal of flow was more frequent in the OCT group than in the induced labor group (P < 0.0001). However, no significant differences were found between spontaneous and induced labor groups. CONCLUSION: Interactions between the contracting uterine body and the relaxing lower segment in oxytocin-induced labor might be associated with differences in uterine arterial flow during contraction between oxytocin-induced and spontaneous labor. However, changes in the intensity of uterine contractions during labor progression might differ between oxytocin-induced and spontaneous labor.

Effects of different sampling points on evaluation of fetal descending aortic flow.

BACKGROUND: Widespread use of fetal aortic blood flow velocity measurements for assessment of fetal circulatory status has been precluded by difficulties in achieving an adequate Doppler insonation angle at particular sampling points. The goal of this study was to evaluate the differences in resistance index (RI) and systolic peak velocity (Vmax) of fetal aortic blood flow velocity waveforms throughout gestation among various Doppler sampling points. METHODS: A total of 551 normal women between 18-41 weeks of pregnancy participated in this study. Pulsed Doppler flow velocity waveforms were acquired from three different aortic sampling points (thoracic portion, beneath the diaphragm, and abdominal portion) of the fetal descending aorta. The Vmax and RI were calculated at the respective sampling points. RESULTS: The Vmax were significantly lower in abdominal portion than those in thoracic portion at every time point (from 69 +/- 11 cm/second in thoracic to 49 +/- 8 cm/second in abdominal portion at 18-19 gestational weeks, p<0.0001), and RI were also lower (from 0.84 +/- 0.05 in thoracic portion to 0.76 +/- 0.05 in abdominal portion at 18-19 gestational weeks, p<0.0001). Significant increase in the Vmax was seen until third trimester (from 58+/-10 cm/second at 18-19 gestational weeks to 113 +/- 13 cm/second at 38-39 gestational weeks beneath the diaphragm, p<0.0001), while the RI remained stable (0.79 +/- 0.04 at 18-19 gestational weeks; 0.80 +/- 0.05 at 38-39 gestational weeks beneath the diaphragm). CONCLUSIONS: In measuring the fetal circulatory status, these data demonstrate that the sampling point should be considered when evaluating the maximum systolic velocity and the resistance index of the fetal descending aorta.