Colour Doppler energy insonation of placental vasculature in monochorionic twins: absent arterio-arterial anastomoses in association with twin-to-twin transfusion syndrome

OBJECTIVE

To determine in vivo whether monochorionic pregnancies complicated by twin-to-twin transfusion syndrome are associated with absence of haemodynamically-compensatory arterio-arterial anastomoses.

DESIGN

Forty monochorionic pregnancies were prospectively recruited for an ultrasonographic survey of the chorionic plate using colour Doppler energy. Arterio-arterial anastomoses were identified by their characteristic bidirectional interference pattern on spectral Doppler. Angioarchitecture was confirmed by postnatal injection study.

SETTING

Fetal medicine tertiary referral centre in London.

MAIN OUTCOME MEASURES

Presence of arterio-arterial anastomoses, development of twin-to-twin transfusion syndrome, survival.

RESULTS

Arterio-arterial anastomoses were detected by colour Doppler energy in 21 pregnancies (53%), and there were no false positives. An arterio-arterial anastomosis was more commonly found in unaffected (n=28) compared to pregnancies affected by twin-to-twin transfusion syndrome (n=12), both by colour Doppler energy [20/28 (71%) is 1/12 (8%); delta=63%, 95% CI 40%-86%] and by postnatal injection study [25/28 (89%) vs 3/12 (25%); delta=64%, 95% CI 37%-91%]. In pregnancies in which no arterio-arterial anastomoses were detected, a diagnosis of twin-to-twin transfusion syndrome was made in 58%, and the perinatal loss rate was 40%, compared with one case of twin-to-twin transfusion syndrome (5%) (P < 0.001) and a loss rate of 12% (P=0.005) in pregnancies in which an arterio-arterial anastomosis was detected. CONCLUSION Twin-to-twin transfusion syndrome is associated with an absence of functional arterio-arterial anastomoses in vivo in monochorionic twin pregnancies. This contributes to our understanding of the pathophysiology of twin-to-twin transfusion syndrome and confirms ex vivo studies demonstrating that twin-to-twin transfusion syndrome is associated with a paucity of superficial anastomoses. Prospective studies are indicated to determine the utility of colour Doppler energy for arterio-arterial anastomoses in predicting risk in monochorionic pregnancies.

The effect of transmission bandwidth on diagnostic accuracy in remote fetal ultrasound scanning

Six subspecialists with considerable experience in fetal ultrasound viewed a selection of pre-recorded ultrasound scans. Scans from 18 patients recorded on VHS video-tape were supplied from five centres in the UK and Ireland, each made on a high-resolution ultrasound machine by an experienced sonologist at a referral centre. Each observer viewed the scans on a large display monitor in an individual viewing booth. The scans were viewed in random order, at randomly selected bandwidths. Observers, who were blinded to both recording and bandwidth, assessed the technical quality on a five-point Likert scale. They also recorded their diagnosis. The six observers each carried out 32 viewing sessions, which gave a total of 192 viewings. There was no significant difference in the perceived technical quality of the scans between the two bandwidths used (P = 0.09). Of the 84 recordings transmitted at 1920 kbit/s, 71 (85%) were diagnosed correctly or 'half correctly' and 13 (15%) were misdiagnosed. Of the 95 recordings transmitted at 384 kbit/s, 66 (69%) were diagnosed correctly or 'half correctly' and 29 (31%) were misdiagnosed. This difference was significant (P = 0.03). The results indicate that although there were no perceived differences in technical quality between recordings transmitted at 384 or 1920 kbit/s, diagnostic accuracy was marginally worse at the lower bandwidth. This suggests that the higher bandwidth conveys more detail and information to the observer, which in turn enables more accurate diagnosis. However, further work is required before a definitive choice can be made about the optimum transmission bandwidth for remote fetal ultrasound studies.

Permeability of human placenta and fetal membranes to thyrotropin-stimulating hormone in vitro

We determined the placental transfer of TSH in an in vitro model of dually perfused isolated lobule in 28 human term placentas by adding varying concentrations (5-60 microIU mL(-1)) of TSH as a single bolus dose to the closed maternal circulation. Transmembrane transfer of TSH was also studied by adding 45 microIU mL(-1) to the maternal or fetal compartment of a dual chamber of fetal membranes in culture. Passage of freely diffusible markers creatinine and antipyrine were also studied in this model. TSH concentration was measured by third generation chemiluminescence assay with a sensitivity of 10 mIU mL(-1). In the perfusion experiments, at physiologic concentrations the slow decline of TSH in the maternal circulation was associated with a small linear increase in fetal levels to 0.11 +/- 0.04% of initial dose at 2 h. The placental transfer rate was 0.08 microIU min(-1). Increasing maternal concentrations of TSH were associated with proportional increases in transfer rate (y = 0.002x; R2 = 0.99) and placental uptake (y = 0.01x; R2 = 0.97). The placental permeability of TSH was 2.4 x 10(-4) mL min(-1) g(-1) and was proportional to its coefficients of diffusion in water and molecular size. The transmembrane transfer and permeability of TSH was comparable to those of the placenta. We conclude that TSH crosses the human term placenta and fetal membranes sparingly.

Neonatal cranial ultrasonographic findings in preterm twins complicated by severe fetofetal transfusion syndrome

OBJECTIVE

To investigate cranial ultrasonographic findings in survivors of monochorionic pregnancies complicated by fetofetal transfusion syndrome.

STUDY DESIGN

Case details of all monochorionic twin pregnancies complicated by fetofetal transfusion syndrome were obtained from the Centre for Fetal Care database for a 3-year period. Fetofetal transfusion syndrome was diagnosed according to ultrasonographic criteria. Eligible for entry were twin pregnancies resulting in live-born preterm infants and complicated by fetofetal transfusion syndrome severe enough to require amnioreduction. Cranial ultrasonographic scans performed within 48 hours of birth were reviewed for evidence of abnormality.

RESULTS

Seventeen pregnancies were eligible for inclusion in the study. Median gestational age was 25 weeks (between 17 and 29 weeks) at diagnosis and 30 weeks (between 25 and 35 weeks) at delivery. Three infants died before ultrasonography could be performed. The remaining 31 twin infants received an early cranial ultrasonographic scan. One of the 31 had a major cerebral infarct; 10 others had evidence of other, more minor, antenatally acquired lesions.

CONCLUSIONS

Both donor and recipient survivors from pregnancies complicated by fetofetal transfusion syndrome are at significant risk for antenatally acquired cerebral lesions. Long-term neurologic follow-up studies are indicated to determine the clinical significance of these lesions.

Effects of antenatal thyrotropin-releasing hormone on fetal heart rate and breathing movements

OBJECTIVE

To determine the effect of maternally administered thyrotropin-releasing hormone (TRH) on fetal heart rate (FHR) pattern and fetal breathing movements (FBM).

METHODS

Prospective observational study of 75 pregnant women between 26 and 34 weeks' gestation in whom pharmacological fetal lung maturation was clinically indicated. Forty-minute recordings were made of FBM or FHR patterns before and after drug administration. Twenty-five received TRH 400 microg as an intravenous bolus, 25 TRH 400 microg in 50 ml 0.9% saline as an intravenous infusion, and 25 acted as controls. Recordings were processed digitally to calculate the change in FHR (n = 45) and FBM parameters (n = 30). The main outcome measures for FHR were number of accelerations and decelerations, baseline rate, overall and short-term variation and duration of high and low variability, while for FBM they were rate, breath-to-breath interval and incidence. Results between groups were compared by analysis of variance.

RESULTS

There was no significant change in FHR, accelerations or variation in any of the groups. Similarly, there was no change in the incidence of FBM. TRH administered as a bolus produced a small statistically but not clinically significant increase in breathing rate (mean delta = 35 breaths/h, p = 0.004), which was not seen in the TRH infusion and control groups.

CONCLUSIONS

Maternally administered TRH as used to enhance fetal lung maturation has no clinically significant direct effect on FHR or FBM patterns.

The consequences of monochorionic placentation

Monochorionic (MC) placentation occurs in two-thirds of monozygous twins and approximately 0.3% of all spontaneous conceptions. Vascular anastomoses within the placenta allow intertwin transfusion to occur, which is in most cases a normal event. However, imbalance in this flow may lead to the clinical sequelae observed, with acute, chronic or reverse intertwin transfusion. Acute transfusion describes the events following the death of one of an MC twin pair in utero, with an approximately 1 in 4 chance of demise or neurological damage in the co-twin. Chronic intertwin transfusion, otherwise termed feto-fetal transfusion syndrome, arises following the gradual flux of blood from one twin (the donor) to its sibling fetus (the recipient). The ensuing polyhydramnios places the pregnancy at risk of preterm amniorrhexis and/or labour, notwithstanding the specific sequelae seen in these fetuses following chronic in utero insult. Reverse transfusion describes the most bizarre form of intertwin transfusion: acardiac twinning. Retrograde perfusion of one of the twins with deoxygenated blood leads to the formation of a non-viable acardiac parasite and a 'pump twin' struggling to maintain the cardiac output required to perfuse both twins.

Absence of expression of RhD by human trophoblast cells

OBJECTIVE

Our purpose was to determine whether the RhD gene is expressed in trophoblast at any stage of gestation.

STUDY DESIGN

Trophoblast and fetal tissue were obtained from 18 pregnancies at 8 to 40 weeks' gestation. Deoxyribonucleic acid and ribonucleic acid were extracted from trophoblast. Complementary deoxyribonucleic acid was synthesized from ribonucleic acid, and reverse transcriptase-polymerase chain reaction was performed using primers specific for the RhD gene. Deoxyribonucleic acid was extracted from fetal tissue to determine the fetal RhD status by means of polymerase chain reaction. Antigen expression was also sought by analytic cytometric analysis (flow cytometry and immunocytochemistry) using a monoclonal anti-D antibody.

RESULTS

Trophoblast was studied from various combinations of RhD-positive and RhD-negative fetuses (on deoxyribonucleic acid) from mothers to find no RhD gene expression in any sample. Flow cytometry and immunocytochemistry confirmed this by demonstrating no RhD antigen sites on trophoblast cells.

CONCLUSION

Contrary to a previous report, we conclude that the RhD gene is not expressed in human trophoblast in any trimester.

Maternal-to-fetal transfer of thyrotropin-releasing hormone in vivo

OBJECTIVE

Our purpose was to determine the transplacental transfer of thyrotropin-releasing hormone at the time of fetal blood sampling.

STUDY DESIGN

Four hundred micrograms of thyrotropin-releasing hormone was given intravenously to 13 pregnant women between 24 and 35 weeks' gestation and maternal-to-fetal transfer of thyrotropin-releasing hormone was determined at fetal blood sampling 1 to 93 minutes later. The fetal thyrotropic response to thyrotropin-releasing hormone was determined by measuring thyroid-stimulating hormone, thyroxine, and prolactin. For comparison, endogenous fetal and maternal levels of thyrotropin-releasing hormone, thyroid-stimulating hormone, thyroxine, and prolactin levels were determined in a further 20 patients undergoing fetal blood sampling between 19 and 35 weeks' gestation. The concentration of thyrotrophin-releasing hormone was measured by radioimmunoassay and thyroid-stimulating hormone, thyroxine, and prolactin by chemiluminescence assay.

RESULTS

Thyrotropin-releasing hormone was undetectable in the maternal circulation, whereas endogenous levels were detectable in the fetus from 19 weeks' gestation (median 150; range 50 to 276 pmol/L) and did not correlate with gestational age. After thyrotropin-releasing hormone injection as an intravenous bolus, peak levels in the mother were attained at 3 minutes (50,000 pmol/L). Maximal transplacental transfer of thyrotropin-releasing hormone occurred within 5 minutes of maternal administration but accounted in fetal blood for only 0.01% of initial dose administered (median 250; 30 to 550 pmol/L). Thyrotropin-releasing hormone-stimulated fetal peak thyroid-stimulating hormone levels occurred within 13 minutes and were higher than maternal values (p < 0.001). There was no change in fetal prolactin level with thyrotropin-releasing hormone therapy.

CONCLUSION

Although maternally administered thyrotropin-releasing hormone crosses the placenta sparingly, it still elicits a thyroid-stimulating hormone but not a prolactin response in the human fetus.

Fetal telemedicine: interactive transfer of realtime ultrasound and video via ISDN for remote consultation

Current referral practice for ultrasonically detected fetal abnormalities contributes to parental anxiety, inconvenience to patients, diagnostic inaccuracy, and general service inefficiency. To determine whether telemedicine would reduce these disadvantages, we established a 30-channel ISDN link between a district general hospital on an island and a subspecialty referral centre approximately 120 km away on mainland Britain. Live ultrasound images of the fetus were transmitted in realtime from a commercial scanner in the hospital using a total data transfer rate of 2 Mbit/s. After decompression at the receiving end, there was almost no perceptible loss of picture quality or frame rate. This report describes the technical aspects of the link and our preliminary experience with it. In the first two months of its operation, the link worked well and the consultants who used it found themselves confidently making diagnoses and carrying out counselling over it. If confirmed, the success of this technology has implications for future referral practice in fetal medicine.

Caesarean section: every woman's right to choose?

Until recently, doctors and patients have been united in wanting lower caesarean section rates. This is changing, and the concept of a more liberal patient-centred choice is gaining credence. Caesarean sections are no longer black and white decisions, but are becoming increasingly discretionary, based on maternal choice, their increasing safety for mother and baby, and recognition of the pelvic damage associated with vaginal birth.

The aetiology and management of twin-twin transfusion syndrome

Twin-to-twin transfusion syndrome presents in the mid-trimester with gross discordance in amniotic fluid volume, and complicates 10-15 per cent of monochorionic twins. Recent studies suggest a primary vascular basis in which a paucity of the bidirectional superficial anastomoses normally found in monochorionic twins is unable to compensate for haemodynamic imbalance resulting from unidirectional transfusion along deeper arterio-venous anastomoses. It is associated with high rates of perinatal mortality from ruptured membranes, hydrops and growth restriction, and a significant morbidity from cardiac and neurological sequelae in particular. Serial aggressive amnioreduction is the current treatment of choice, with survival in around two thirds of cases. In the remaining third, with features suggesting a poor outcome, selective fetocide may have a role. Current attempts at vascular ablative therapies have been associated with inferior survival rates, but the long term therapeutic goal remains the identification and ablation of the shared chorionic vasculature.

Transport and metabolism of thyrotrophin-releasing hormone across the fetal membrane

To determine the transfer and metabolism of TRH by human fetal membranes, the bidirectional transport and uptake of TRH was investigated by adding 125I-labeled TRH (100,000 cpm) or commercial TRH either to the maternal or the fetal compartment of an in vitro model of cultured human fetal membranes obtained from term and preterm placenta. Transmembrane transfer was also studied in the presence of 200 microM p-hydroxy-mercuriphenyl-sulphonic acid (p-HMSA), a dipeptidase enzyme inhibitor. Creatinine and heparin were used as an internal markers. Metabolites of TRH were separated from intact molecules by gel filtration on Sephadex G-10. The structural integrity of the membrane was confirmed by electron microscopy. The transmembrane transfer of radiolabeled and commercial TRH were comparable across both preterm and term placenta. When transport was studied from the maternal to fetal side, the maternal concentration of TRH declined rapidly from 100% at time 0 to 19.31 +/- 2.26% at 8 h with a concomitant increase in the fetal concentration from undetectable to a maximum of 2.56 +/- 0.38% with a fetomaternal ratio of 0.16 +/- 0.01. Transfer of TRH from the fetal to maternal compartment was similar to that of maternal to fetal. Chromatography of maternal and fetal media showed that TRH was metabolized by the membrane into small molecular weight fragments. Treatment of the membrane with p-HMSA increased TRH transport from the maternal to fetal compartment to 18.12 +/- 0.91 (P < 0.001) with an fetomaternal ratio of 0.35 +/- 0.02 (P < 0.001). Although transmembrane transfer of TRH from the fetal to maternal side was also increased by p-HMSA, levels achieved were less than that from maternal to fetal (12.26 +/- 1.50%; P < 0.05). These results suggest that the human fetal membrane acts as an enzymatic barrier to the bidirectional transfer of TRH from 24 weeks gestation.

Relationship between change in amniotic fluid index and volume of fluid removed at amnioreduction

OBJECTIVE

To determine the relationship between the change in amniotic fluid index (AFI) and the volume of fluid removed at amnioreduction.

METHODS

In a prospective study of 20 twin and 19 singleton pregnancies undergoing amnioreduction for severe polyhydramnios, AFI was measured immediately before and after the procedure and was correlated with the volume of fluid withdrawn.

RESULTS

A significant linear relationship was found between AFI change and the volume drained in all pregnancies (Y = -4.2X; R2 = 0.49; P = .002). This relationship was similar in singleton and twin pregnancies. However, there was a significant absolute difference in AFI change between singleton and twin pregnancies of 7.9 cm (95% confidence interval 0.41, 15.2; P = .04).

CONCLUSION

These findings support the use of the four-quadrant AFI as a semiquantitative index of amniotic fluid volume. This relationship can be used to predict the drainage volume required to achieve a target AFI with amnioreduction and thus avoid repeated AFI measurements during the procedure itself.

Liposomal thyroxine: a noninvasive model for transplacental fetal therapy

Drugs that cross the placenta sparingly are currently given directly to the fetus by invasive procedures. We investigated whether anionic small unilamellar (SUV) liposomes of different lipid compositions enhanced the transfer and uptake of T4 in an in vitro model of perfused human term placenta. T4-encapsulated anionic liposomes were prepared using lecithin (F-SUV) or distearoyl phosphatidylcholine (S-SUV) with cholesterol and dicetylcholine. The size distribution, encapsulation efficiency, and stability were determined in blood-based media. The transfer kinetics of free and liposomally encapsulated T4 were studied in a dually perfused isolated lobule of human term placenta, with creatinine and liposomal carboxyfluorescein as marker substances. Concentrations of T4 and rT3 were measured by RIA. T4 crossed the placenta sparingly (1.9 +/- 0.5%) because it was metabolized to rT3 (9.2 +/- 1.3%). Transplacental transfer of T4 was significantly increased by F-SUV (15.8 +/- 2.1%; P < 0.001) and S-SUV liposomes (7.1 +/- 1.2%; P < 0.001), with a concomitant decrease in fetal rT3 levels (P < 0.001). Placental uptake of F-SUV (13.5 +/- 2.0%; P < 0.001) was greater than that of S-SUV liposomes (6.7 +/- 0.8%; P < 0.001). Our data suggest that anionic liposomes increase transplacental transfer of T4. If confirmed in vivo, liposomes may provide an alternative noninvasive method of drug delivery to the fetus.

Effect of antenatal administration of thyrotrophin releasing hormone on fetal flow velocity waveforms

AIM

To determine whether antenatal administration of thyrotrophin releasing hormone (TRH), to promote lung maturation, alters blood flow through the fetal middle cerebral, umbilical artery, or ductus arteriosus and through the maternal uterine arteries.

METHODS

The effect of transplacentally administered TRH on the fetal circulation was prospectively evaluated in 30 patients between 24 and 34 weeks' gestation. TRH (400 micrograms) was given to the mother intravenously either as a bolus or an infusion. Fetal effects were determined by measuring the maximum velocity and pulsatility index (PI) in middle cerebral artery, ductus arteriosus, uterine artery and umbilical artery Doppler waveforms. Measurements were made immediately before, and 10 and 60 minutes after maternal TRH administration.

RESULTS

Intravenous injection of TRH had no significant effect on PI in the uterine, umbilical, or middle cerebral artery and the ductus arteriosus within 60 minutes of administration in either group.

CONCLUSION

The antenatal use of TRH in conjunction with steroids for fetal lung maturity does not affect utero-placental or fetal haemodynamic variables, as measured by Doppler. These findings, therefore, do not support the suggestion that antenatal intravenous administration of TRH either as bolus or infusion may have immediate adverse vascular effects in the fetus.

Pharmacokinetics and pharmacodynamics of TRH during pregnancy

OBJECTIVE

To determine the pharmacokinetics and pharmacodynamics of thyrotropin-releasing hormone (TRH) in pregnant women.

METHODS

Twenty-four pregnant and eight nonpregnant women were given 400 micrograms TRH as either intravenous infusion or bolus. Serial venous samples were collected for TRH, TSH, thyroxine, and prolactin assay.

RESULTS

When given as bolus, mean (+/- standard error of the mean) peak plasma concentration (50 +/- 5.2 and 73 +/- 5.1 ng/mL, P < .01), elimination half life (4.3 +/- 0.3 and 6.3 +/- 0.4 minutes, P < .001), and area under the curve (156.4 +/- 14.8 and 340.1 +/- 32.8 ng/mL/minute, P < .001) in pregnant subjects were reduced compared with controls, whereas plasma clearance (45.4 +/- 6.5 and 23.6 +/- 2.1 mL/kg/minute, P < .01) and volume of distribution (27.8 +/- 1.8 and 19.0 +/- 1.3% body weight, P < .01) were increased. When given by infusion, steady-state concentration (6.6 +/- 0.5 and 9.8 +/- 0.9 ng/mL, P < .01) and elimination half-life (4.6 +/- 0.5 and 6.3 +/- 0.3 minutes, P < .05) were lower in pregnant subjects than in controls. Thyrotropin-releasing hormone kinetics were independent of mode of administration. Although basal TSH and thyroid hormone concentrations were similar in patients and controls, the TSH response to TRH was blunted in pregnant subjects compared with controls (9.3 +/- 0.6 and 16.4 +/- 1.4 microIU/mL, P < .001). The basal (3187 +/- 488 and 147 +/- 16 mIU/L) and maximal prolactin response (6193 +/- 426 and 1316 +/- 106 mIU/L) were increased in pregnant subjects compared with controls (P < .001).

CONCLUSION

The peak plasma concentration and elimination half-life of TRH are reduced during pregnancy because of the increased volume of distribution and rapid clearance. Mode of administration does not affect TRH pharmacokinetics, but the maternal pharmacodynamic response differs in patients receiving bolus compared with infusion.

Prenatal sonographic diagnosis of cleidocranial dysostosis

Cleidocranial dysostosis is an autosomal dominant disorder characterized by absence or hypoplasia of the clavicles, skull abnormalities, and abnormal dentition. The prenatal diagnosis of this condition has been reported once previously in a known high-risk pregnancy. In this report we describe the prenatal findings of cleidocranial dysostosis at 19 weeks' gestation in a woman affected with this disorder but undiagnosed before the fetal scan. This report is unique in the sense that an autosomal dominant condition diagnosed in the fetus led to a similar diagnosis in the mother.

Survey of obstetricians' personal preference and discretionary practice

OBJECTIVE

To determine obstetricians personal choices in relation to Down syndrome screening and mode of delivery for themselves or their partners.

STUDY DESIGN

Structured anonymous postal survey. All 282 obstetric consultants, senior registrars and registrars in NHS obstetric units within London's M25 region were surveyed.

RESULTS

The response rate was 73% (206). Fifty one per cent (105) chose to have elective amniocentesis/CVS without a previous screening test when maternal age was > or = 35 years and 11% (23) when < 35 years. Of the remainder, the majority wanted both maternal serum screening and nuchal translucency rather than a single screening test. In relation to mode of delivery, 17% (33) of obstetricians chose elective caesarean section (CS) in the absence of any clinical indication. Of those who chose CS, 88% did so out of fear of perineal damage. However when faced with a mid-cavity instrumental delivery in the second stage, only 5% (8) wanted CS, the remainder choosing operative vaginal delivery. With an uncomplicated breech presentation, only 27% (55) opted for external cephalic version while 57% (114) chose elective CS.

CONCLUSION

This study demonstrates interventionist attitudes among a sizeable percentage of obstetricians in relation to antenatal screening and their own preferred mode of delivery. It suggests that obstetricians regard management options not normally available to pregnant women as valid choices for themselves or their partners.

Maternofetal transfer of thyrotrophin-releasing hormone: effect of concentration and mode of administration

We studied the effect of maternal concentration and mode of administration on transfer rate of TSH-releasing hormone (TRH) in an in vitro model of dually perfused isolated lobule of human term placenta. Varying concentrations (4-40 microg dL(-1)) of TRH were added either to the open maternal circulation to mimic an infusion or as a single bolus dose to the closed maternal circulation. TRH was measured by RIA. Perfusion efficiency in each experiment was determined by using antipyrine and creatinine as diffusable markers. At a concentration equivalent to the usual clinical dose of 400 microg, transplacental transfer of TRH was 0.4 +/- 0.1%, with an fetal/maternal ratio of 0.01 +/- 0.003. Placental clearance rate (y = 0.07x; R2 = 0.97; p < 0.001; n = 28) and uptake of TRH (y = 0.40x; R2 = 0.95; p < 0.001) in the closed experiments increased exponentially with increasing maternal concentration. Placental clearance (y = 0.05x; R2 = 0.99; p < 0.001; n = 30), and uptake of TRH (y = 0.35x; R2 = 0.98; p < 0.01) under steady state also correlated with maternal TRH concentration. For a given concentration, placental clearance and uptake of TRH was comparable whether given as a bolus or an infusion. We conclude that TRH is transferred sparingly across the human term placenta and its transfer rate is a function of the maternal concentration of TRH and not its mode of administration.

Fetal testing in twins

The incidence of twin pregnancies continues to rise with increasing use of assisted fertility techniques. The search for accurate methods of chorionicity determination and aneuploidy screening, and the outcome following multi-fetal pregnancy reduction dominate the recent literature. In addition, debate on the aetiology and management of the transfusional complications of monochorionicity continues.

Medical amnioreduction with sulindac to reduce cord complications in monoamniotic twins

OBJECTIVE

Cord entanglement is a common complication of monoamniotic twins and it is associated with high perinatal mortality. Apart from preterm delivery, no treatment has previously been used to reduce the risks of this complication. We postulated that reducing amniotic fluid volume would stabilize fetal lie and reduce the risk of cord compression.

STUDY DESIGN

Cord entanglement was documented in three cases of monoamniotic twins in the midtrimester. Sulindac was administered to the mother. Amniotic fluid index, fetal urine output, and umbilical artery and ductus arteriosus Doppler waveforms were investigated before and during treatment by use of real-time and pulsed Doppler techniques.

RESULTS

Sulindac was associated with a dose-related reduction in amniotic fluid index and fetal urine production without alteration in fetal flow velocity waveforms. Fetal lie stabilized after commencement of treatment. All six twins were delivered with no complications.

CONCLUSION

Medical amnioreduction with sulindac is a new management option in monoamniotic twins to reduce cord complications.

Fetal telemedicine: six month pilot of real-time ultrasound and video consultation between the Isle of Wight and London

DESIGN

Prospective audit of first six months.

SETTING

Referral from a district general hospital on the Isle of Wight to a comprehensive tertiary referral service, the Centre for Fetal Care at Queen Charlotte's Hospital 120 km away in London.

PARTICIPANTS

Women whose pregnancy was suspected, or at risk, of fetal abnormality.

INTERVENTIONS

Remote consultation by transmitting ultrasound and video in real-time over ISDN 30 telephone lines. Contemporaneous questionnaire to referring practitioner and patient.

MAIN OUTCOME MEASURES

Frequency, indication, technical success and duration of consultation. Qualitative and semi-quantitative image quality. Effect of teleconsultation on need for physical referral.

RESULTS

Twenty-nine women underwent 39 teleconsultations, and image quality was sufficient for diagnosis in all but one. Fetal abnormalities were present in 76%. Referral in person was required for only four women, significantly fewer than the 13 the referring hospital indicated would have been physically referred in the absence of this service (P < 0.001). Most mothers were counselled by the specialist "face-to-face' over the link, and 80% felt teleconsultation reduced their anxiety.

CONCLUSIONS

A fetal telemedicine service is technically and clinically feasible. This demonstration suggests that such a service reduces the need for physical referral while increasing the rate of consultation, allowing better selection of patients who might benefit from referral. Further evaluation in a variety of clinical settings is now indicated, along with cost-benefit analysis.

High failure rate of postmortem karyotyping after termination for fetal abnormality

OBJECTIVE

To determine the failure rate of karyotyping from samples taken after termination of pregnancy for fetal abnormality.

METHODS

Perinatal autopsy reports over a 12-month period were reviewed to identify those with cytogenetic studies performed after termination of pregnancy for fetal abnormality.

RESULTS

During the audit period, there were 104 terminations for fetal abnormality. In 89 fetuses, fetal skin (n = 85), placenta (n = 62), or other samples (n = 8) were obtained for postmortem cytogenetic analysis. In 24 (27%) fetuses, postmortem tissues did not yield a karyotype result. The failure rate of post-termination karyotyping was significantly influenced by delivery-sampling interval, but not by gestational age, type of tissue sampled, use of potassium chloride, or aneuploidy. Of the 24 cases for which no post-termination karyotype was obtained, 16 had had successful pre-termination karyotyping, resulting in only eight of 89 (9%) cases in the overall series not having a final karyotype.

CONCLUSION

The high failure rate for post-termination karyotyping suggests that a pre-termination procedure is necessary if parents wish to have almost 100% certainty that cytogenetic information will be available for later genetic counseling.

Transfer and metabolism of thyrotropin releasing hormone across the perfused human term placenta

The transport and uptake of TRH was investigated in the maternal-fetal-placental unit of perfused human term placenta. The degradation of TRH in biological fluid was first determined by incubating [125I]TRH with 100 microL 50% maternal or cord sera with or without pretreatment with 200 microM of p-hydroxymercuriphenyl sulfonic acid (p-HMSA), a proline dipeptidase inhibitor. Transplacental transfer of TRH was then studied by adding 10 microCi of [125I]- or [3H]TRH to the maternal circulation of dually perfused isolated lobule of human term placenta with or without 200 microM p-HMSA. Creatinine was used as an internal marker. The rate of degradation of TRH (P < 0.001) and inhibition by p-HMSA were significantly higher in maternal than cord sera (P < 0.05). In the maternal circulation, TRH concentration declined rapidly from 100% at time 0 to 33.5 +/- 1.2% at 120 min. The fetal concentration increased from undetectable levels to a maximum of 1.8 +/- 0.3% at 120 min with a low feto-maternal ratio (0.08 +/- 0.02). Perfusion in the presence of p-HMSA, however, did not significantly change fetal concentration, or the maternal and fetal concentration-time integral levels of TRH. Chromatography of maternal, fetal, and placental homogenates showed that TRH was metabolized by the placenta into small molecular weight fragments predominantly released in the maternal circulation. These results suggest that human placenta acts as an enzymatic barrier to the free passage of TRH.

Prenatal diagnosis by minimally invasive first-trimester transcervical sampling is unreliable

OBJECTIVE

We investigated whether reliable prenatal diagnosis is possible from fetal cells harvested transcervically in first-trimester pregnancies.

STUDY DESIGN

Fetal cells were obtained transcervically from 87 women undergoing pregnancy termination. Fetal gender was determined in 51 pregnancies with three different polymerase chain reaction techniques and in 36 pregnancies with fluorescent in situ hybridization. In known male pregnancies the number of male fetal cells present was also determined.

RESULTS

Polymerase chain reaction detected male deoxyribonucleic acid in up to 79% of cases in male pregnancies and up to 45% of cases in female pregnancies. Fetal gender was correctly predicted in up to 72% of cases with fluorescent in situ hybridization. However, fetal cells were identified in < 40% of informative male pregnancies and were present in low numbers-0.7% to 3.4% in swabs and 4.4% to 24.8% in flushes.

CONCLUSION

The use of fetal cells obtained by minimally invasive first-trimester transcervical sampling is unreliable for prenatal diagnosis.

Common iliac artery flow velocity waveforms in fetuses with a single umbilical artery: a longitudinal study

OBJECTIVES

In fetuses with a single umbilical artery the entire blood flow to the placenta is transported through the common and internal iliac arteries from the side of the single artery, whereas the pelvic vessels from the side of the missing artery do not participate in the fetoplacental circulation. The aim of this study was to investigate the effect of gestational age on pelvic arterial blood flow in fetuses with single umbilical artery.

DESIGN

In 15 fetuses with a single umbilical artery (SUA), common iliac artery flow velocity waveforms were studied longitudinally using high resolution colour Doppler ultrasonography at three gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 37 weeks. The pulsatility index was measured in each common iliac artery and mixed model analysis of variance was used to examine the effect of gestational age and side.

RESULTS

There was a highly significant difference in pulsatility index between common iliac arteries at all gestational ages, the values always being higher on the side that did not participate in the fetoplacental circulation (P < 0.001). For increasing gestation, the pulsatility index fell significantly in the SUA side but remained high in the non-SUA side (P < 0.001).

CONCLUSIONS

This study shows that the asymmetry in the pelvic arterial blood flow in fetuses with SUA increases as pregnancy progresses, consistent with decreasing vascular resistance in the placenta and increasing resistance in the lower extremities.

Molecular genetic etiology of twin reversed arterial perfusion sequence

OBJECTIVE

Our purpose was to determine whether the twin reversed arterial perfusion sequence (acardiac anomaly) results from fertilization of the first or second polar body.

STUDY DESIGN

Placental or fetal tissue was obtained from nine twin sets discordant for twin reversed arterial perfusion. After deoxyribonucleic acid extraction, the polymerase chain reaction was used to amplify five polymorphic microsatellite repeats. The products were differentiated by polyacrylamide gel electrophoresis, and patterns were compared within twin sets.

RESULTS

Deoxyribonucleic acid fingerprinting patterns were identical in all twin sets for all primer pairs. It is calculated that the chance that any of the acardiac twins resulted from fertilization of either the first or second polar body is <4% and the chance that they all resulted from polar body fertilization is <0.001%.

CONCLUSION

Twins discordant for the twin reversed arterial perfusion sequence anomaly are monozygous. Our results exclude polar body fertilization as a likely cause of this condition.

Second-trimester echogenic bowel and intraamniotic bleeding: association between fetal bowel echogenicity and amniotic fluid spectrophotometry at 410 nm

OBJECTIVE

Our purpose was to determine whether the presence of heme pigments in amniotic fluid is associated with the ultrasonographic findings of increased fetal bowel echogenicity in the second trimester.

STUDY DESIGN

Spectrophotometric analysis of amniotic fluid for optical density at 410 nm was prospectively performed to study the presence of heme pigments in (1) 104 pregnancies undergoing second-trimester amniocentesis for routine cytogenetic indications and (2) in 14 pregnancies undergoing amniocentesis for prenatal karyotyping because of fetal strongly echogenic bowel. In the routine amniocentesis group the fetal small bowel echogenicity was assessed immediately before amniocentesis and classified as nonechogenic (n = 64), mildly echogenic (n = 36), or hyperechogenic (n = 4) with the fetal iliac wing and liver used as references. Only amniotic fluid specimens that were obtained at the first attempt and that were not blood-stained were included in this study, with the first milliliter being discarded in all samples.

RESULTS

In the routine amniocentesis group abnormal amniotic fluid optical density readings were significantly more frequent in fetuses with increased bowel echogenicity compared with those with nonechogenic bowel (8/40 [20%] vs 3/64 [5%], respectively; p < 0.001). In the hyperchogenic bowel group abnormal amniotic fluid optical density readings were found in four samples (29%). Overall, 12 of 54 fetuses (22%) with increased bowel echogenicity had a detectable peak at 410 nm. Three of the 12 (25%) fetuses with echogenic bowel and positive readings for hemoglobin were chromosomally abnormal.

CONCLUSIONS

Fetal small bowel echogenicity is associated with the presence of heme pigments in amniotic fluid as determined by amniotic fluid optical density at 410 nm. Swallowing of amniotic fluid after intraamniotic bleeding seems implicated in the etiology of second-trimester echogenic bowel in both euploid and aneuploid fetuses.

Hydrostatic and osmotic pressure gradients produce manifestations of fetofetal transfusion syndrome in a computerized model of monochorial twin pregnancy

OBJECTIVE

In spite of recent advances in the assessment and treatment of fetofetal transfusion syndrome, its underlying mechanism remains controversial. We aimed to determine whether the clinical features of fetofetal transfusion syndrome could be explained by unidirectional or bidirectional intertwin transfusion along placental vascular anastomoses.

STUDY DESIGN

We constructed a dynamic computerized model of monochorial twin fetoplacental units on the basis of numerous interrelated hemodynamic, osmotic, and metabolic physiologic variables. The circulations were then linked by various combinations of direction and number of arteriovenous anastomoses.

RESULTS

With unidirectional anastomoses disease severity, characterized by disparity in blood solids, depended on donor arterial pressure but not on the number of anastomoses. In the chronic state water movement resulting from raised osmotic pressure in the recipient and reduction in the donor produced hydroosmotic pressure equilibrium, reducing anastomotic flow to near zero. Atrial natriuretic peptide-driven urine production was markedly increased in the recipient because of the raised vascular hydrostatic pressure component. With bidirectional anastomoses recirculation between twins reduced discordancy in colloids and hematocrit, and the clinical picture was determined by the degree of asymmetry in the number of connections.

CONCLUSIONS

Severe manifestations of fetofetal transfusion syndrome can be explained by unidirectional intertwin transfusion and lesser degrees by asymmetric bidirectional transfusion.

Is isolated second-trimester hyperechogenic bowel a predictor of suboptimal fetal growth?

Hyperechogenic bowel has been described as a normal variant in second-trimester fetuses, but also in association with cystic fibrosis, chromosomal abnormalities, congenital infection, intestinal obstruction and intra-amniotic bleeding. These fetuses are also at risk for poor perinatal outcome, mainly due to intrauterine growth retardation. In this report we examine the potential of ultrasonographic detection of isolated fetal hyperechogenic bowel in the second trimester as a marker of subsequent suboptimal fetal growth. Second-trimester fetuses with hyperechogenic bowel in comparison to controls had a greater incidence of birth weight below the 10th centile (6/48, 12.5% vs. 4/149, 2.7%, respectively; p = 0.01) and lower mean birth weight (3176 g (SD 741 vs. 3499 g (SD 493)), respectively; p = 0.001). There was no difference in the prevalence of preterm delivery in both groups (3/48, 6.3% vs. 8/149, 5.4%, respectively; p = 0.7). This study suggests that second-trimester fetuses normally-grown with isolated hyperechogenic bowel are at risk for suboptimal fetal growth.

Prevalence of cystic fibrosis mutations in pregnancies with fetal echogenic bowel

OBJECTIVE

To determine the prevalence of the most common cystic fibrosis mutations in pregnancies complicated by fetal echogenic bowel by using DNA testing.

METHODS

Forty-five pregnancies with fetal echogenic bowel were studied prospectively for cystic fibrosis mutations. Using polymerase chain reaction, DNA from fetal amniocytes (n = 21), fetal blood (n = 5), or parental blood (n = 19) was amplified and tested for delta F508, G551D, G542X, and 621 + 1G-->T cystic fibrosis mutations, which account for about 85% of the mutations in the British population. In selected cases, further mutations were tested according to the parental ethnic background.

RESULTS

Only one of the 26 fetuses screened was heterozygous for cystic fibrosis mutations. Among 38 parental samples screened from the remaining 19 pregnancies, cystic fibrosis mutations were detected in two cases, only one of the parents being a carrier in each case. The prevalence of cystic fibrosis carrier status in fetal and parental samples (1:26 and 1:19, respectively) is within the expected prevalence in the British population (1:25). No fetuses were affected by cystic fibrosis in this series, but five were found to have growth restriction, two trisomy 21, two congenital infection, and two bowel obstruction.

CONCLUSION

Our results suggest that ultrasonographic detection of fetal echogenic bowel is not associated with an increased prevalence of cystic fibrosis mutations in pregnancies at low risk for this disease.

Accuracy of prenatal diagnosis of renal agenesis with color flow imaging in severe second-trimester oligohydramnios

OBJECTIVE

Our purpose was to examine the potential of color flow imaging to assess the presence of renal arteries in second-trimester pregnancies complicated by severe oligohydramnios.

STUDY DESIGN

Thirty-three consecutive second-trimester pregnancies referred with severe oligohydramnios were prospectively studied with high-resolution color Doppler ultrasonography to establish the presence or absence of renal arteries. Prenatal findings were correlated with the presence or absence of fetal kidneys at postmortem or postnatal examination.

RESULTS

Neither renal artery was visualized in eight fetuses; postmortem examination confirmed bilateral renal agenesis in seven and unilateral renal agenesis with a contralateral atrophic multicystic kidney in the other. Only one renal artery was seen in three; postmortem examination demonstrated unilateral renal agenesis in two fetuses and bilateral multicystic dysplastic kidneys in the other. Postmortem or postnatal evaluation confirmed the presence of both kidneys in all 22 fetuses in which both renal arteries were identified prenatally.

CONCLUSIONS

Color Doppler ultrasonography is useful in the prenatal evaluation of fetuses with severe second-trimester oligohydramnios to demonstrate the presence or absence of renal arteries. This technique should be added to the armamentarium of prenatal tests to evaluate second-trimester fetuses with severe oligohydramnios.

Ultrasonographic measurement of the dividing membrane in twin pregnancy during the second and third trimesters: a reproducibility study

OBJECTIVE

Our purpose was to examine the reproducibility of intertwin membrane thickness measurements used to predict chorionicity in twin pregnancies.

STUDY DESIGN

Twenty-seven twin pregnancies were scanned with high-resolution ultrasonography on 52 occasions during the second and third trimesters. Two observers, blind to other criteria of chorionicity, measured the dividing membrane twice in five different sites (total measurements 1040). The data were log-transformed and the coefficient of repeatability calculated as a measure of intraobserver variability. Interobserver variability was estimated by the Bland and Altman 95% limits of agreement. Random variation was assessed with the restricted maximum likelihood procedure in Genstat.

RESULTS

The overall estimate of the coefficient of repeatability was 2.14, indicating that 95% of repeated measurements would be expected to be within 114% of each other. Measurements taken close to the placenta (up to 3 cm) were the most repeatable and displayed no bias when repeated. Coefficients of repeatability at this site ranged from 1.42 to 1.91, with no evidence of consistent differences between monochorionic and dichorionic twins. Gestational age was not significantly associated with membrane thickness for any of the models. The pregnancy type x subject x observer and pregnancy type x subject x site interactions were statistically significant (p < 0.001 and p < 0.005, respectively), implying that interobserver variability depends on the subject being measured, the site of sampling, and chorionicity.

CONCLUSION

Ultrasonographic measurement of membrane thickness has high intraobserver and interobserver variability in the second and third trimesters. Our findings provide an explanation for the suboptimal accuracy reported with this method in determining chorionicity in the second and third trimesters.

Discordant blood flow velocity waveforms in left and right brachial arteries in growth-retarded fetuses

OBJECTIVE

To determine if the increase in cerebral blood flow ("brain-sparing" effect) with fetal hypoxemia is associated with discordant hemodynamics in the upper extremities.

METHODS

We studied 12 fetuses with severe growth retardation, absent or reverse end-diastolic blood flow in the umbilical artery, and low pulsatility index (PI) in the middle cerebral artery, and 12 appropriately grown control fetuses with normal fetoplacental Doppler studies. The right and left brachial arteries were identified by high-resolution color Doppler ultrasonography, and the PI was measured in each brachial artery.

RESULTS

All growth-retarded fetuses had lower impedance indices in the right than in the left brachial artery (mean delta PI 1.0, 95% confidence interval [CI] 0.7-1.3, P < .001). No differences in the brachial artery impedance indices were found in control fetuses matched for gestational age (mean delta PI 0.0, 95% CI -0.2 to 0.2).

CONCLUSIONS

Left and right brachial artery blood flow velocity waveforms are discordant in fetuses with growth retardation and cerebral vasodilation. Because the right arm receives its blood supply from the same source as the brain (brachiocephalic artery) and given the proximity of the left subclavian artery to the ductus arteriosus, we speculate that this might be the result of increased blood flow into the brachiocephalic circulation and/or functional differences in the distribution of left and right ventricular output within the aortic arch in response to fetal hypoxemia.

Prenatal diagnosis of cerebral arteriovenous malformation using color Doppler ultrasonography: case report and review of the literature

Aneurysms of the vein of Galen are rare, representing less than 1% of all intracranial arteriovenous malformations. In the fetus, however, almost all cerebral arterial malformations involve the vein of Galen, usually presenting in the neonatal period with severe cardiac failure leading to neonatal death. In this report we present a case of arteriovenous malformation involving the vein of Galen detected prenatally at 35 weeks with the use of color Doppler ultrasonography. The literature is reviewed in an attempt to delineate the role of prenatal ultrasonography in the diagnosis and its impact on perinatal outcome.

Accuracy of prenatal determination of RhD type status by polymerase chain reaction with amniotic cells

OBJECTIVE

Our purpose was to determine the accuracy of RhD typing by use of amniocytes obtained at amniocentesis in RhD-negative women.

STUDY DESIGN

One hundred thirty-five RhD-negative women undergoing amniocentesis for management of suspected alloimmunization (n = 95) or routine second-trimester cytogenetic indications (n = 40) were studied. Amniocytes were then used as template to amplify specific portions of the Rh D and Rh CcEe genes by polymerase chain reaction. The fetal RhD type was confirmed by serologic techniques either after fetal blood sampling or cord blood samples at birth.

RESULTS

Thirty-six fetuses were serologically typed as RhD negative and all 36 were typed RhD negative by polymerase chain reaction. Ninety-eight fetuses were serologically typed as RhD positive; of these, 96 were correctly typed as RhD positive and two were incorrectly typed as RhD negative, with an overall error rate of 1.4%. Both of the errors occurred in a single batch of six samples tested at the same time. In one of these cases the fetus had mild Rh alloimmune disease and required exchange transfusion at birth. In the second case the fetus had severe hydrops fetalis and died in utero at 28 weeks. Deoxyribonucleic acid isolated from fetal blood was tested with the same polymerase chain reaction technique after delivery, and in both cases the fetus was correctly typed as RhD positive. Deoxyribonucleic acid amplification repeatedly failed in one case.

CONCLUSION

Prenatal fetal RhD typing by polymerase chain reaction with amniotic fluid cells is accurate and reliable. In sensitized pregnancies it allows early management of Rh disease and avoids invasive procedures in RhD-negative fetuses. In nonsensitized pregnancies it avoids the use of anti-RhD immunoglobulin after invasive procedures or during pregnancy. To eliminate the possibility of genetic and laboratory sources of errors, we suggest using different sets of primers at two different loci (e.g., exon 4 to 5 and exon 10).

Acute maternal hydration in third-trimester oligohydramnios: effects on amniotic fluid volume, uteroplacental perfusion, and fetal blood flow and urine output

OBJECTIVE

Our purpose was to determine whether acute maternal hydration in pregnancies with third-trimester oligohydramnios (1) increases amniotic fluid index and hourly fetal urine production rate and (2) alters uteroplacental perfusion and fetal blood flow.

STUDY DESIGN

Ten women with third-trimester oligohydramnios (amniotic fluid index < or = 5 cm) and 10 controls with normal amniotic fluid volume (amniotic fluid index > 7 cm) were prospectively recruited for this study. Maternal plasma and urine osmolality, amniotic fluid index, hourly fetal urine production rate, and Doppler flow velocimetry of maternal uterine artery and fetal umbilical, descending aorta, middle cerebral, and renal arteries were determined before and after oral hydration by having the patient drink 2 L of water over 2 hours.

RESULTS

There was a significant reduction in maternal plasma (p < 0.05) and urine osmolality (p < 0.0001) in both groups after short-term oral hydration. Hydration increased amniotic fluid volume in women with oligohydramnios (mean change in amniotic fluid index 3.2 cm, 95% confidence intervals 1.1 to 5.3; p < 0.02) but not in those with normal amniotic fluid volume (mean change in amniotic fluid index -2.0, 95% confidence intervals -4.1 to +0.2). The hourly fetal urine production rate, however, did not increase in either group (mean change in hourly fetal urine production rate 3.5 ml/hr, 95% confidence intervals -11.7 to +18.7 and -6.8 ml/hr, 95% confidence intervals -2.9 to -10.7, respectively). Hydration was associated with an increase in uterine artery mean velocity in the oligohydramnios group (mean change in mean velocity 16.7 cm/sec, 95% confidence intervals 8.0 to 25.3; p < 0.006) but not in controls (mean change in mean velocity 1.2 cm/sec, 95% confidence intervals -19.7 to +22.1). There was no change in pulsatility index or in velocity in any of the fetal vessels studied in either group.

CONCLUSIONS

Short-term maternal oral hydration increases the amniotic fluid index in women with third-trimester oligohydramnios. Although the mechanism for this effect remains unclear, it could not be accounted for by fetal urination in this study but instead was associated with improved uteroplacental perfusion.

Ablation of acardiac twin by alcohol injection into the intra-abdominal umbilical artery

BACKGROUND

Twin reversed arterial perfusion sequence is a rare complication of monochorionic twinning, in which the normal pump twin perfuses the abnormal acardiac twin in a reversed fashion via an artery-to-artery placental anastomosis. Mortality in the normal twin exceeds 50% as a result of preterm labor, polyhydramnios, and congestive heart failure.

CASE

A twin pregnancy complicated by the twin reversed arterial perfusion sequence developed early hemodynamic decompensation in the pump twin with increasing size of the acardiac twin. Ablation of the acardiac twin at 23 weeks' gestation was achieved successfully by injecting 1 mL of absolute alcohol into the intra-abdominal portion of the single umbilical artery.

CONCLUSION

Direct ultrasound-guided intravascular injection of absolute alcohol is an easy and straightforward technique to occlude circulation to the acardiac twin. This vessel can be identified easily by color Doppler ultrasonography away from the main venous trunk. Selection of this target, rather than occlusion at the level of the umbilical cord, could reduce the risks of cord accidents and inadvertent intravenous injection of the ablative material.

Uterine artery blood flow response to correction of amniotic fluid volume

OBJECTIVE

Our purpose was to investigate whether acute alterations of amniotic fluid volume affect uteroplacental perfusion.

STUDY DESIGN

Three groups of patients of comparable gestational age were studied in a fetal medicine referral unit: (1) eight pregnancies with severe polyhydramnios because of twin-twin transfusion syndrome undergoing therapeutic amnioreduction, (2) seven with severe oligohydramnios undergoing diagnostic amnioinfusion, and (3) six control women having invasive procedures of similar duration without manipulation of amniotic fluid volume. Color Doppler imaging was used to measure uterine artery impedance index values and quantitative blood flow before and within 15 minutes of the end of the procedure.

RESULTS

Quantitative flow measurements increased after amnioreduction (74% median increase of volume flow, range 22% to 329%, p < 0.01) and decreased after amnioinfusion (33% median decrease of volume flow, range 17% to 51%, p < 0.05). Impedance index values increased after amnioinfusion (25% median increase in pulsatility index, range 4% to 71%, p < 0.05) and did not alter with amnioreduction. There were no significant changes in the control group.

CONCLUSION

Acute changes in amniotic fluid volume alter uteroplacental perfusion. In twin-twin transfusion syndrome amelioration in uterine flow may improve fetal condition and explain in part the success of serial amnioreduction therapy.