Ultrasound evaluation of polyhydramnios and twin pregnancy

A systematic review of amniotic fluid assessments in twin pregnancies

The objectives of this systematic review were to examine the reproducibility of sonographic estimates of amniotic fluid volume (AFV) in twin pregnancies, compare the association of sonographic estimates of AFV with dye-determined AFV, and correlate AFV with antepartum, intrapartum, and perinatal outcomes in twin pregnancies. Studies were included if they were adequately powered and investigated antepartum, intrapartum, and/or perinatal adverse outcome parameters in twin gestations. Studies with comparable populations and exclusion criteria were merged into forest plots. Data comparing the accuracy of AFV assessment, correlation of AFV with gestational age, and adverse outcomes were tabulated. Five of the 6 studies investigating AFV by the amniotic fluid index as a function of gestational age reported data fitting a quadratic equation, with fluid volumes peaking at mid gestation and then declining. This trend was less pronounced when AFV was assessed by the single deepest pocket (2 of 4 studies reporting a quadratic fit). Polyhydramnios was associated with prematurity in 2 of 4 studies (1 amniotic fluid index and 1 single deepest pocket), and oligohydramnios was associated with prematurity in 1 single deepest pocket study. Stillbirth was the only intrapartum outcome reported in more than 1 study. Perinatal outcomes associated with polyhydramnios included neonatal death (P < .05 in 1 of 2 studies), low Apgar scores (1 of 2 studies), neonatal intensive care unit admission (1 of 2 studies), and low birth weight (2 of 3 studies).

Management of Multiple Pregnancy: Prenatal Care???Part I

Over the past 20 years, the number and rate of multiple births have dramatically increased in the United States. The rise in multiple births is mainly attributable to the increased use of ovulation-inducing drugs and the newly developed assisted reproductive technologies such as in vitro fertilization. Multifetal gestation is associated with an increased risk of perinatal morbidity and mortality. Multiple births account for an increasing percentage of low-birth-weight infants, preterm births, and infant mortality. In this section, we address the management of the multifetal pregnancy, focusing on the maternal physiology, the diagnosis, the pregnancy outcomes, and the antenatal management of multiple gestation.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader should be able to describe the effects of the rising rate of multiple pregnancies on perinatal morbidity and mortality, to recall the complications of diagnosing and treating abnormalities of multiple pregnancies, and to list the many changes that occur in both the mother and the fetuses in multiple pregnancies.

Characteristics of monochorionic-diamniotic growth-retarded twins during the third trimester

The goal of this study was to assess the characteristics of monochorionic-diamniotic (MD) growth-retarded twin infants with twin-twin transfusion syndrome (TTTS) compared with those without TTTS during the third trimester. Retrospective analyses of the growth patterns and amniotic fluid volumes were performed on 5 MD twin pregnancies in which one or both twins showed growth retardation with TTTS, and the results weve compared with those without TTTS. Eighty-three percent of growth-retarded twin infants without TTTS in MD twin gestation showed an asymmetric growth pattern, while all TTTS cases showed a symmetric pattern (p < 0.05). Polyhydramnios of the co-twin was found in 80% of TTTS cases, while no polyhydramnios was found in patients without TTTS (p < 0.05). Assessment of growth patterns and amniotic fluid volume may be useful to exclude the possibility of TTTS in MD growth-retarded twin pregnancies during the third trimester.

Prevalence of polyhydramnios in the third trimester in a population screened by first and second trimester ultrasonography

AIMS

To determine the prevalence of polyhydramnios in a routine antenatal population, in which first and second trimester ultrasound screening for fetal abnormality had been performed and to examine the outcome in these pregnancies.

METHODS

A retrospective analytical survey of all obstetric ultrasound examinations performed in a university teaching hospital over a thirty-six month period. Polyhydramnios was defined as either the measurement of a single deepest pool of liquor > 8 cm (AFV) or according to the amniotic fluid index, the sum of a four quadrant measurement > 24 cm (AFI). Using the stated definitions, polyhydramnios was diagnosed in 37 women, 16 of whom had a raised AFI. The main outcomes of interest included the mode of onset of labour and mode of delivery (rates of spontaneous and induced labour, cesarean section deliveries), birth weight, presence or absence of fetal anomalies, and the perinatal outcome.

RESULTS

The prevalence of polyhydramnios in this study is lower (0.15% AFI > 24 cm and 0.36% AFV > 8 cm) than in previous studies. The association between polyhydramnios, maternal diabetes mellitus (10.8%), fetal abnormalities (5.4%) and fetal macrosomia (10.8%) was also lower than in past reports. There was a better overall fetal outcome compared with previous studies and no perinatal deaths were seen.

CONCLUSIONS

In this study, the prevalence of polyhydramnios in the third trimester was lower than in previous studies, as well as being associated with a better prognosis. This may have been the result of a combination of several factors. These include the introduction of multi-level ultrasound screening for fetal abnormality, and the improved care of diabetic women, and mothers with rhesus iso-immunisation.

Fetal biometry and outcome in monochorionic vs. dichorionic twin pregnancies; a retrospective cross-sectional matched-control study

Fetal biometry, amniotic fluid volume distribution and perinatal outcome were determined in a retrospective, cross-sectional matched-control study design, including 20 monochorionic (MC) twin pregnancies and 20 dichorionic (DC) twin pregnancies (historic controls). Intertwin differences for fetal abdominal circumference were larger in the MC subset than in the DC subset. Fetofetal transfusion syndrome, based upon a combination of oligohydramnios in one sac and polyhydramnios in the other sac, existed in 40% (8 of 20) of the MC twin pregnancies, but in none of the DC twin pregnancies. Mean gestational age at delivery was significantly shorter in the MC subset (30.9 weeks) than in the DC subset (34.3 weeks). The perinatal death rate was significantly higher in MC twin pregnancies (50%) than in DC twin pregnancies (15%). No differences were established for intertwin weight estimates by ultrasound and birth weight between both subsets. The poor perinatal outcome in monochorionicity is mainly a result of the degree of premature delivery.

Neonatal neurologic characteristics of preterm twin infants <1,250 gm birth weight

The study objectives were to determine the incidence, time of onset, and clinical characteristics of neonatal neurologic injury in preterm twin infants <1,250 gm birth weight. Forty-one twin infants of birth weight 929 gm +/- 160 and 27.3 +/- 1.96 weeks gestation were evaluated and compared to 225 singleton infants <1,250 gm. Seventeen infants were monozygotic and 24 dizygotic. Six of the 9 monozygotic pregnancies were complicated by the polyhydramnios/oligohydramnios syndrome; a weight discordancy of >20% was observed in 8 of the monozygotic twin sets and polycythemia (hematocrit >65%) in 3 infants. Nine (22%) of the 41 infants died. Periventricular-intraventricular hemorrhage (PV-IVH) developed in 11 (27%) of 41 infants and was severe in 9 (22%) infants. IVH was noted on day 1 (n = 2), day 2 (n = 3), and day 3 (n = 6). IVH developed in 69 (30%) of the 225 singletons and was severe in 28 (12%) infants. Twin infants were more likely to have been delivered via cesarean section, to have required intubation in the delivery room, and to have been administered surfactant as compared with singletons (P < .01). It was concluded that preterm twin infants <1,250 gm are at high risk for developing severe IVH, and that the onset of IVH was within the first 3 postnatal days in all cases.

Ultrasonographic measurement of amniotic fluid volume in normal diamniotic twin pregnancies

OBJECTIVE

Our purpose was to determine the amniotic fluid volume in normal diamniotic twins.

STUDY DESIGN

The single amniotic fluid index for both twin members, the maximum depth and width of each twin's largest pocket, were measured every 4 to 6 weeks between 15 and 40 weeks in 91 normal diamniotic twin gestations. The two-diameter pocket in each twin was determined as its largest pocket's depth multiplied by its width. Normal twin gestations were defined as those with <20% birth weight discordance, appropriate for gestational age, no fetal anomalies, delivery at > or = 37 weeks, and normal newborns. Amniotic fluid index values, depths, and two-diameter pockets were stratified into 2-week intervals and transformed into base 10 logarithms because of their nongaussian distributions. The correlations of these measurement with gestational age were evaluated. Their means and 90%, 95%, and 98% confidence intervals were determined.

RESULTS

The amniotic fluid index changed significantly with gestational age. However, depths and two-diameter pockets did not. The amniotic fluid index rose from 15 to 24 weeks, plateaued until 36 weeks, and then declined. The 90%, 95%, and 98% confidence intervals for each twin's depth were 2.4 to 7.9, 2.1 to 8.8, and 1.9 to 10 cm, respectively (mean 4.3 cm). These respective confidence intervals for each twin's two-diameter pocket were 8 to 44, 7 to 52, and 5 to 63 cm2 (mean 19 cm2). The amniotic fluid index confidence interval curves were plotted from the log (amniotic fluid index)=0.8276 + 0.01675x-0.0000001900x4, R2=0.78, p=0.002 (where x is gestational age).

CONCLUSION

The amniotic fluid volume in normal diamniotic twin pregnancies was established ultrasonographically. Only the amniotic fluid index changed significantly with gestational age. These findings may have significance in the clinical management of twin gestation.

Twin transfusion: pathological studies of the monochorionic placenta in liveborn twins and of the perinatal autopsy in monochorionic twin pairs

Vascular injections of 21 monochorionic placentas from liveborn twins were scored for chorionic surface vessel anastomoses and for venous return areas. The results were correlated with neonatal birth weight and first hematocrit. Weight and hematocrit differences did not correlate with each other or with placental anastomoses. There was a relationship between weight and placental area to the individual twin. In some cases, weight differences between monochorionic twins may be the result of placental differences rather than chronic transfusion. Seventeen perinatal autopsies of monochorionic twin pairs were reviewed for plethora/pallor and for organ and body weights. Cardiac hypertrophy was present in three autopsies. Cardiac hypertrophy may be a measure of chronic twin transfusion in the recipient. The lighter twin was as likely to be plethoric as the heavier. Plethora postmortem is a poor measure of chronic transfusion because of confounding factors, particularly acute twin transfusion. As a result of these studies, placental anatomy is speculated to be complexly rather than directly related to clinical outcome.

Twin growth problems: causes and sonographic analysis

Understanding the significant increased risks associated with twin pregnancies requires knowledge of the embryogenesis of twins and the unique placental characteristics seen only in twin gestations. Dizygotic "fraternal" twins, 70% of all twins, are at relatively low risk when compared with monozygotic twins, largely due to abnormalities seen in association with monochorionic placentation. The sonographic determination of chorionicity and amnionicity allows better estimation of pregnancy risk--up to 50% mortality in monochorionic-monoamniotic twins. Careful evaluation of intrauterine twin growth assists in the early identification of fetal abnormalities because normal twin growth should parallel that of singleton pregnancies until late in the third trimester. A number of the unique complications affecting growth in twin pregnancies are discussed, including twin transfusion syndrome, the "stuck twin" phenomenon, twin embolization syndrome, and development of acardiac twins.

Amniotic fluid volume: fluid dynamics and measurement technique

Evaluation of amniotic fluid volume is an important aspect of obstetrical ultrasound. Several methods are currently used to describe amniotic fluid volumes. The most common are the subjective assessment of fluid and the semiquantitative methods. The reproducibility of these methods is excellent in experienced hands. Because of the multiple methods used to assess fluid, both oligohydramnios and polyhydramnios have numerous definitions. Regardless of which definition is used, it is clear that both of these entities are associated with a variety of fetal and maternal conditions. Abnormal amniotic fluid volume may be the only or earliest sonographic sign of an obstetrical problem. Therefore, it is important that sonologists are familiar with amniotic fluid volume assessment. Although subjective and semiquantitative techniques may produce similar results, a numerical scale is no substitute for experience and training. One should be able to recognize lesser degrees of fluid abnormality and be able to assess the trend of amniotic fluid volume in serial examinations.

Diagnosis of polyhydramnios in early gestation: indication for prenatal diagnosis?

Previously published reports have indicated that idiopathic polyhydramnios may be associated with trisomies 18 and 21 and that chromosomal analysis is indicated. Furthermore, the natural history and fetal outcome of polyhydramnios diagnosed in early gestation have not been well delineated. We identified 138 pregnancies with polyhydramnios prior to 26 weeks' gestation. Of 131 complete cases, 21 were diagnosed as severe, 18 as moderate, and 92 as mild polyhydramnios. Congenital abnormalities were noted in 18 of 21 severe cases (86 per cent). Two of the remaining three cases were twin-to-twin transfusion. Thirteen of 18 cases with moderate polyhydramnios (72 per cent) were associated with anomalies; six of the remaining cases were twin-to-twin transfusion. Sixteen of 92 cases of mild polyhydramnios (17 per cent) were associated with congenital abnormalities. In 69 of 76 cases of mild hydramnios not associated with anomalies (91 per cent), the hydramnios resolved prior to delivery. Only 2 of 16 (13 per cent) associated with anomalies resolved. In 4 of 5 cases (80 per cent) with moderate hydramnios and no anomalies, the amniotic fluid volume was normal on subsequent ultrasound. No case of moderate polyhydramnios associated with anomalies or maternal conditions nor any case of severe polyhydramnios resolved. There were seven cases of chromosomal abnormalities in this series; all were associated with sonographic findings in addition to the presence of polyhydramnios. On the basis of these data, we doubt the benefit of amniocentesis following the early diagnosis of idiopathic polyhydramnios in the absence of other ultrasound findings.

Twin-twin transfusion syndrome

Twin-twin transfusion syndrome associated with acute polyhydramnios in one sac and severe oligohydramnios in the other, which characteristically is diagnosed between 18 and 28 weeks, is associated with a high mortality rate for the involved twins. Patients who are managed without intervention have essentially 100% perinatal mortality. Nineteen patients with this diagnosis were treated at Good Samaritan Medical Center over a 5-year period. Because of the known perinatal mortality and because of early experiences with the twin-twin transfusion syndrome, we began to actively intervene in such patients with various modes of therapy. As experience was gained, it was found that repeated therapeutic amniocenteses, if performed before severe maternal abdominal distention or labor, appears to be beneficial.

The "stuck twin" phenomenon: ultrasonographic findings, pregnancy outcome, and management with serial amniocenteses

Thirteen consecutive twin pregnancies affected by the "stuck twin" phenomenon were reviewed to determine the potential benefit of serial amniocenteses. The fetal survival rate for the eight pregnancies that underwent serial amniocenteses was 69% (11 of 16 fetuses). This is significantly improved compared with a fetal survival rate of 20% among the five preceding pregnancies managed without serial amniocenteses at the same institution (p = 0.01). It is also markedly improved compared with a combined fetal survival rate of 16% among 48 previously reported pregnancies with the stuck twin phenomenon managed without serial amniocenteses (p less than 0.0001). Survival correlated with the absence of concomitant pregnancy complications (i.e., maternal hypertension or intractable labor) and with the absence of severe fetal structural abnormalities. Procedural complications occurred in three of eight pregnancies (37.5%) managed with serial amniocenteses and was attributed as a cause of fetal death in one case. Two of 11 survivors (18%) had complications after serial amniocenteses including brain infarction and renal tubular necrosis. Serial amniocenteses may significantly improve the survival rate of twin gestations affected by the stuck twin phenomenon but may be associated with complications among survivors.