Caudal regression syndrome versus sirenomelia: a case report.

We describe a newborn with clinical features of sirenomelia including fused lower limbs with medial position, absence of fibula, anal atresia, bilateral renal agenesis, and a single large umbilical artery. Recent literature describing the etiology of sirenomelia and relationship to caudal regression syndrome is reviewed.     

Sirenomelia: a review of embryogenic theories and discussion of the differences from caudal regression syndrome

Objective: To discuss the pathological features of sirenomelia in the light of our 10 cases and review the current theories.

Methods: We identified 10 patients with sirenomelia from our hospital database. All clinical details and the autopsy features of 10 cases were noted.

Results: Of the 10 children with sirenomelia seven had bilateral renal agenesis, three had bladder agenesis and one had a renal hypoplasia. Single umbilical artery was found in 60% of children with sirenomelia. External genitalia was ambiguous in seven of 10 patients.

Conclusions: Even though the etiology of caudal regression syndrome (CRS) and sirenomelia remains unknown we tend to believe that sirenomelia and CRS might be different entities.     

Sirenomelia--a rare cause of an oligoanhydramnion in the second trimester--a case report

Sirenomelia is a rare, but complex and lethal malformation. It is caused by a primary defect of the caudal axial skeleton and damage to the primary streak, which appears due to a vascular steal phenomenon. Sirenomelia appears sporadic with an incidence of 1-64,000 births. A risk for sirenomelia can be also found in patients with poorly controlled diabetes mellitus and in monocygotic twins. Leading ultrasound findings are fusioned lower extremities, bilateral renal agenesis, single umbilical artery and a distinct oligohydramnios. 3D ultrasound and color Doppler sonography can additionally be used for diagnostic, as well as amnioninfusion. There are 3 forms of sirenomelia, depending on missing or presence of the feet it is distinguished as sympus apus, monopus or dipus. We are presenting a case of sirenomelia with sympus dipus, which was transferred for further diagnostic of severe oligohydramnios in 21 weeks of gestation by the gynecologist.     

First trimester diagnosis of sirenomelia: a case report and review of the literature

Sirenomelia sequence is a rare lethal pattern of congenital anomalies characterized by a number of hallmark skeletal anomalies, including fusion of the lower extremities or a single lower limb, bilateral renal agenesis or dysgenesis with absent or hypoplastic renal arteries, oligohydramnios, and the presence of aberrant vasculature. The etiology is still controversial. Prognosis is very poor, with the babies being stillborn or succumbing soon after birth. In the second trimester, oligohydramnios due to renal agenesis makes the diagnosis of sirenomelia difficult. Conversely, in the first trimester, the amniotic fluid volume is usually normal, unrelated to the fetal urine production. Therefore, a first-trimester or early second trimester anatomic survey of the fetus is proposed as preferable and more accurate for the diagnosis of this rare anomaly. In this article, we report a case of sirenomelia detected by two- and three-dimensional ultrasound in the 11th week of gestation and the associated literature is discussed.     

The association of single umbilical artery with cytogenetically abnormal pregnancies

The clinical significance of the absence of one of the two umbilical arteries (single umbilical artery) lies in its association with congenital malformations. Whether this association includes cytogenetic abnormalities is less clear. A retrospective review of all detected chromosomally abnormal pregnancies at the University of Maryland was carried out. Of 109 cytogenetically abnormal pregnancies, the number of umbilical cord vessels could be documented in 53 cases. Six (11.3%) had a single umbilical artery. A single umbilical artery was noted in two of nine fetuses (22.2%) with trisomy 18 and in two of six fetuses (33.3%) with trisomy 13. Two other unusual chromosomal constitutions were noted in cases of a single umbilical artery. None of the 11 fetuses with sex chromosome abnormalities (including eight with monosomy X) had a single umbilical artery. Of 18 fetuses with trisomy 21, none had a single umbilical artery. This study suggests that a single umbilical artery is preferentially associated with certain karyotypic abnormalities and that trisomy 21 does not appear to be associated with a single umbilical artery.     

Prenatal diagnosis of sirenomelia

OBJECTIVE: What kind of diagnostical methods are usual to detect fetal sirenomelia? MATERIAL AND METHODS: The prenatal diagnosis of fetal sirenomelia combined with bilateral renal agenesis, oligohydramnios and single umbilical artery in a 24-year-old woman, gravida 2, para 1, at a gestational age of 18 + 3 weeks is described in this case report. RESULTS: This fetal malformation was an accidental sonographic found, and caused after confirming diagnosis by amnoinfusion and amniocentesis, the termination of pregnancy. Genetic examination revealed tetrasomia 13. CONCLUSIONS: The sonographic finding of oligohydramnios should cause an exactly sonographical examination with amnioinfusion. In case of sirenomelia genetical examination is necessary.     

Uterine and fetal umbilical artery flow velocity waveforms in normal first trimester pregnancies

In 85 normal singleton pregnancies between 8 and 13 weeks gestation, Doppler flow velocity waveform recordings were attempted from the left and right uterine artery and fetal umbilical artery. Acceptable waveforms were obtained from the uterine arteries in 83 and from the fetal umbilical artery in 61 of the 85 pregnancies. There was virtually no difference between the left and right uterine artery on average. The marked decrease in pulsatility (PI) and resistance (RI) indices from both uterine arteries reflects the ongoing process of secondary trophoblast invasion into the muscular part of the spiral arteries. Absent end-diastolic velocities were observed in 59 of 61 fetal umbilical artery flow velocity waveform recordings. PI values from the fetal umbilical artery suggest unaltered umbilical placental vascular resistance during the first trimester of pregnancy.     

Doppler velocimetry in the fetus with a single umbilical artery.

OBJECTIVE: To study Doppler velocimetry in fetuses with a single umbilical artery (SUA) as compared to normal. STUDY DESIGN: Private and clinic patients were referred to a perinatal center: 45 with SUA and 124 randomly selected fetuses with a three-vessel cord were studied from 18 to 41 weeks' gestation. Color Doppler flow and energy were utilized to evaluate the umbilical arteries at the fetal abdominal wall as well as the course around the bladder. In addition to Doppler velocimetry, an anatomic survey, estimated fetal weight (EFW) and amniotic fluid index (AFI) were assessed at each examination. RESULTS: Doppler velocimetry in SUA demonstrated indices in the normal range but lower than in normal cords from 26 weeks until near term. Anatomic anomalies were found in 8.9% of SUA as compared to 4.8% for three-vessel cords. Intrauterine growth restriction (IUGR) was seen in four cases of SUA and none in the control group. EFW and AFI for both groups were virtually identical. CONCLUSION: SUA cords theoretically carry a normal blood volume, and the decreased resistance to flow and larger arterial diameter allow this to occur. Anomalies and IUGR are elevated in infants with SUA. Overall, EFW and AFI were the same in both groups of patients.     

A comparison of fetal abdominal circumference measurements and Doppler ultrasound in the prediction of small-for-dates babies and fetal compromise

A total of 145 pregnancies clinically suspected of being small-for-dates was studied at presentation with a single measurement of the fetal abdominal circumference and Doppler studies of the umbilical and arcuate arteries. The abdominal circumference measurement gave the best prediction of the small-for-gestational-age (SGA) baby (sensitivity 73%, umbilical artery sensitivity 47%, arcuate artery sensitivity 29%). The umbilical artery measurement gave the best prediction of antenatal fetal compromise; the performance of the tests was compared for a fixed sensitivity of 100% (i.e. all cases of antenatal compromise would be detected), the specificity of the umbilical artery measurement was 77%, abdominal circumference measurement 12% and arcuate artery measurement 2%. In our data, umbilical artery studies were not a sensitive predictor of the SGA baby but they did give an accurate prediction of the potentially compromised SGA fetus.     

Hyrtl's anastomosis, the only connection between the two umbilical arteries. A study in full term placentas from AGA infants with normal umbilical artery blood flow

BACKGROUND: The aim of this study was to describe the variable anatomy in the anastomosis between the umbilical arteries for better understanding of the physical characteristics of the umbilical flow velocity waveform (FVW). METHODS: The arterial system of 67 placentas from pregnancies with normal umbilical FVW and resulting in a full-term AGA infant was visualized by angiography. The method allowed study of the anatomy of the anastomosis between the umbilical arteries and calculation of the relative placental area supplied by each umbilical artery. RESULTS: In 60 cases there was one anastomosis between the umbilical arteries, in one case there were two, in four the anastomosis was absent, and another two cases had a single umbilical artery. The anastomosis was represented by a vessel, a fenestration or coalescence of the umbilical arteries. In case the anastomosis diameter was of at least that of the umbilical arteries, they supplied in mean 26% and 74% (+/- 8.2%) of the placental area respectively. When the anastomosis diameter was smaller than that of the umbilical arteries their supply areas were in mean 41% and 59% (+/- 6.0%) respectively. In placentas lacking anastomosis the two umbilical arteries supplied 45% and 55% (+/- 2.6%) respectively, indicating a higher degree of symmetry. CONCLUSIONS: By using angiography we were able to demonstrate the variable anatomy of the anastomosis of Hyrtl. We found the occurrence and width of the anastomosis was correlated to the symmetry in size between the supply areas of each umbilical artery.     

A comparison of fetal abdominal circumference measurements and Doppler ultrasound in the prediction of small-for-dates babies and fetal compromise

Summary. A total of 145 pregnancies clinically suspected of being small-for-dates was studied at presentation with a single measurement of the fetal abdominal circumference and Doppler studies of the umbilical and arcuate arteries. The abdominal circumference measurement gave the best prediction of the small-for-gestational-age (SGA) baby (sensitivity 73%, umbilical artery sensitivity 47%, arcuate artery sensitivity 29%). The umbilical artery measurement gave the best prediction of antenatal fetal compromise; the performance of the tests was compared for a fixed sensitivity of 100% (i. e. all cases of antenatal compromise would be detected), the specificity of the umbilical artery measurement was 77%, abdominal circumference measurement 12% and arcuate artery measurement 2%. In our data, umbilical artery studies were not a sensitive predictor of the SGA baby but they did give an accurate prediction of the potentially compromised SGA fetus.     

Uterine and umbilical artery Doppler are comparable in predicting perinatal outcome of growth-restricted fetuses

Objective  To compare umbilical and uterine artery Doppler in predicting outcome of pregnancies suspected of fetal growth restriction (FGR).
Design  A prospective study included 353 singleton pregnancies complicated by an FGR fetus.
Setting  University Hospital setting.
Sample  Pregnancies suspected of FGR diagnosed by ultrasound fetal biometry during a 5-year period.
Main outcome measure  Perinatal outcome in relation to uterine and umbilical artery Doppler.
Methods  The women underwent Doppler examination of the umbilical and uterine arteries. Results from the uterine, but not the umbilical artery, were blind to the woman and managing obstetrician. The Doppler results were related to perinatal outcomes including small for gestational age newborns, caesarean delivery, premature delivery (<37 weeks of gestation) and admission of the newborn to a neonatal intensive care unit.
Results  Abnormal uterine artery Doppler velocimetry was seen in 120 (33.4%) pregnancies and abnormal umbilical artery Doppler in 102 (28.4%). There was a statistically significant correlation between abnormal Doppler of both the umbilical and uterine arteries and adverse outcome of pregnancy. The two vessels were comparable in predicting adverse outcome. Women with normal umbilical artery Doppler (251) were analysed separately. Abnormal uterine artery Doppler, seen in 61 (24.3%) of those women, showed a statistically significant correlation for adverse outcome of pregnancy.
Conclusions  Doppler examinations of the uterine and/or the umbilical arteries seem to be comparable as predictors of outcome in pregnancies complicated by FGR. Including uterine artery Doppler in the surveillance of growth-restricted fetuses might detect a group of pregnancies at high risk, even though the umbilical artery Doppler was normal.     

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

Objective 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.     

Uterine and fetal umbilical artery flow velocity waveforms in normal first trimester pregnancies

Summary. In 85 normal singleton pregnancies between 8 and 13 weeks gestation, Doppler flow velocity waveform recordings were attempted from the left and right uterine artery and fetal umbilical artery. Acceptable waveforms were obtained from the uterine arteries in 83 and from the fetal umbilical artery in 61 of the 85 pregnancies. There was virtually no difference between the left and right uterine artery on average. The marked decrease in pulsatility (PI) and resistance (RI) indices from both uterine arteries reflects the ongoing process of secondary trophoblast invasion into the muscular part of the spiral arteries. Absent enddiastolic velocities were observed in 59 of 61 fetal umbilical artery flow velocity waveform recordings. PI values from the fetal umbilical artery suggest unaltered umbilical placental vascular resistance during the first trimester of pregnancy.     

Umbilical and uterine artery flow velocity waveforms in pregnancy associated with major fetal abnormality

Flow velocity waveforms from the umbilical artery and branches of the uterine artery in the placental bed were recorded using continuous wave Doppler ultrasound. The records of 26 patients with pregnancy complicated by major fetal abnormality were reviewed to determine the changes of a primary fetal disturbance. The systolic/diastolic (A/B) ratio was used as an index of blood flow resistance. In 13 of the 26 patients the umbilical artery waveform systolic/diastolic ratio was high. It is postulated that in these patients there is a process of obliteration of small arteries in the placenta that is triggered by the abnormal fetus. In all patients the uterine artery waveform was normal. In seven of these 13 patients the infant had a birthweight greater than 10th centile. Placental weights were examined. A small placenta expressed as either low weight for gestational age or low placental/fetal weight ratio was associated with a normal umbilical artery waveform. It is suggested that fetuses in these groups have a low growth potential. In contrast a high placental/fetal weight ratio was associated with an abnormal umbilical artery waveform pattern.     

Prenatal diagnosis of sirenomelia

Sirenomelia sequence associates a fusion of inferior legs with renal anomalies until bilateral agenesis. It is a rare and lethal polymalformation. The purpose of the ultrasonographic study is to identify the sirenomelia as early as possible during pregnancy and to differentiate it from caudal regression syndrome. A case of sirenomelia diagnosed early is reported together with a review of the literature. The ultrasonographic diagnosis, associated defects, the interest of color Doppler study of abdominal vasculature are discussed. Antenatal ultrasonographic diagnosis should be obtained as early as possible, before 20th gestational week at the latest. Color Doppler is helpful to confirm the diagnosis in case of bilateral renal agenesis. The main differences between sirenomelia and caudal regression syndrome (which requires a very different genetic counselling) are summarized in a table.     

Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation

Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time waveforms as an index of blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially 'at risk' pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries (less than 90 micron diameter) in the tertiary stem villi in a standard microscopic field (mean 18.5 fields/placenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1-2 arteries/field) than in both the normal and control groups (7-8 arteries/field). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi.     

Sirenomelia in uneventful pregnancy

A rare case of sirenomelia at 38 weeks of gestation is reported. Fusion of the lower extremities and incomplete development of the bony pelvis was associated with agenesis of the urinary and genital systems, anorectal atresia and a single large umbilical artery. There was complete situs inversus of the single lower limb. This was composed of two partially fused femurs, a common tibia without fibula, and a rudimentary foot having three metatarsal bones and their corresponding toes. The present case was also interesting for its association with hypoplasia of the lungs. The pathogenesis of sirenomelia is discussed.     

Umbilical and uterine artery flow velocity waveforms in pregnancy associated with major fetal abnormality

Summary. Flow velocity waveforms from the umbilical artery and branches of the uterine artery in the placental bed were recorded using continuous wave Doppler ultrasound. The records of 26 patients with pregnancy complicated by major fetal abnormality were reviewed to determine the changes of a primary fetal disturbance. The systolic/diastolic (A/B) ratio was used as an index of blood flow resistance. In 13 of the 26 patients the umbilical artery waveform systolic/diastolic ratio was high. It is postulated that in these patients there is a process of obliteration of small arteries in the placenta that is triggered by the abnormal fetus. In all patients the uterine artery waveform was normal. In seven of these 13 patients the infant had a birthweight > 10th centile. Placental weights were examined. A small placenta expressed as either low weight for gestational age or low placental/feta1 weight ratio was associated with a normal umbilical artery waveform. It is suggested that fetuses in these groups have a low growth potential. In contrast a high placental/fetal weight ratio was associated with an abnormal umbilical artery waveform pattern.     

Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation

Summary. Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time wave-forms as an index of blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially 'at risk' pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries (<90 μm diameter) in the tertiary stem villi in a standard microscopic field (mean 18·5 fields/placenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1–2 arteries/field) than in both the normal and control groups (7–8 arteries/field). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi.