Objective To characterize amniotic pressure (AP) in pregnancies with normal amniotic fluid volume. Design Observational study, mainly cross‐sectional. Setting Fetal medicine unit within a tertiary referral hospital. Subjects Patients undergoing transamniotic invasive procedures in whom amniotic fluid volume was subjectively assessed as normal on ultrasound. Those beyond 16 weeks with a deepest vertical pool on ultrasound <3.0 or >8.0 cm were excluded. Overall 194 pregnancies were studied on 232 occasions between 7 and 38 weeks gestation. Interventions Manometry readings referenced to the top of the maternal abdomen were obtained via a fluid‐filled line from the needle hub and either connected to a pressure transducer (n= 190) or held vertically against a ruler (n−42). Main outcome measures AP in mm Hg, AP corrected for gestational age (z scores), semi‐quantitative ultrasonic indices of amniotic fluid volume, clinical variables. Results AP in singleton pregnancies increased with advancing gestation (P<0.001), and the sigmoid‐shaped regression curve plateaued in the mid‐trimester. AP z scores were not influenced by volume‐related phenomena such as twin gestation, the deepest vertical pool, or amniotic fluid index, nor by maternal age, parity, gravidity, fetal sex, or subsequent spontaneous preterm delivery. Conclusions These findings suggest that AP is not principally determined by intrauterine volume. We speculate that AP, which reflects change in uterine tension as a function of radius, may instead be determined by gestation‐specific anatomical and hormonal influences on gravid uterine musculature. A reference range for AP has been constructed for use in amnioinfusion and amnioreduction procedures.
Amniotic band syndrome is a sporadic condition that may result in constriction bands, amputation and multiple craniofacial, visceral and body wall defects. It occurs in 1/1,200 to 1/15,000 live births. Most cases present with multiple congenital anomalies that are incompatible with life. A small group of fetuses shows isolated limb constrictions that may cause severe limb dysfunction or limb amputation if left untreated. Successful in utero surgical lyses of constriction rings have been reported. We report a case of constriction amniotic bands involving both legs and compromising blood flow to the distal extremity. The constriction ring was successfully released by a minimally invasive endoscopic surgical technique avoiding severe limb dysfunction or foot amputation.
Objective To determine the effect of neuromuscular blockade on fetal heart rate and its variation. Design Case control study. Setting Tertiary referral fetal medicine unit in a London teaching hospital. Subject Forty women with rhesus iso‐immunisation requiring an intravascular fetal blood transfusion between 28 and 34 weeks gestation. Intervention Intravascular injection of pancuronium to the fetus prior to fetal blood transfusion in 20 cases. Main outcome measures Comparison between the group receiving pancuronium and the control group with regard to differences in perceived fetal activity and computer derived numerical indices of fetal heart rate and fetal heart rate variation after fetal blood transfusion. Results After transfusion in the control group, there were fewer perceived fetal movements, a small reduction in fetal heart rate but no differences in number of fetal heart rate accelerations or measures of fetal heart rate variation. In the study group, pancuronium produced no change in fetal heart rate despite a virtual abolition of perceived fetal movements and fetal heart rate accelerations. Measures of fetal heart rate variation were reduced by 60%. Comparison of the pre‐ to post‐transfusion changes between the two groups showed significant differences for all fetal heart rate indices. Conclusion Fetal activity accounts for more than half the measured variation of the human fetal heart rate.
The suggestion that amnioinfusion improves umbilical artery Doppler indices of downstream resistance in oligohydramnios by relieving cord compression was investigated by obtaining waveforms before and immediately after amnioinfusion in 16 pregnancies with severe oligohydramnios. There was no significant difference in the change in umbilical artery pulsatility index (PI) between 11 pregnancies in which amniotic fluid volume was restored (mean ΔPI = ––0.07, 95% confidence interval ––0.17 to +0.07), and 5 pregnancies in which immediate vaginal leakage of infused fluid prevented restitution of amniotic fluid volume. Fetal heart rate did not change significantly in either group. End-diastolic frequencies did not return with restitution of amniotic fluid volume in the 2 pregnancies in which they were absent before infusion (absent in 1, reverse in 1). This study suggests that restitution of amniotic fluid volume in human pregnancies complicated by severe oligohydramnios does not acutely alter the umbilical artery PI.
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