Ultrasound evaluation of amniotic fluid volume. II. The relationship of increased amniotic fluid volume to perinatal outcome

Idiopathic polyhydramnios and pregnancy outcome: systematic review and meta-analysis

OBJECTIVE

To analyze outcomes of singleton pregnancies with idiopathic polyhydramnios through a systematic review and meta-analysis.

METHODS

Electronic databases, including MEDLINE, OVID, EBSCO, Cochrane collection and Science Citation Index, were searched from 1946 to 2019. Gray literature and tables of contents of relevant journals were also screened. Prospective and retrospective studies with a control group were included. Two authors independently reviewed the abstracts retrieved from the literature search. Inclusion criteria were: studies documented in English, singleton pregnancy and idiopathic polyhydramnios determined by amniotic fluid volume assessment on ultrasound. Exclusion criteria were: maternal diabetes, fetal structural or chromosomal anomaly, alloimmunization and intrauterine fetal infection.

RESULTS

Twelve studies met the inclusion criteria, giving a total of 2392 patients with idiopathic polyhydramnios and 160 135 patients with normal amniotic fluid volume. Pregnancies complicated by idiopathic polyhydramnios were at a higher risk of neonatal death (odds ratio (OR), 8.68 (95% CI, 2.91-25.87)), intrauterine fetal demise (OR, 7.64 (95% CI, 2.50-23.38)), neonatal intensive care unit admission (OR, 1.94 (95% CI, 1.45-2.59)), 5-min Apgar score < 7 (OR, 2.21 (95% CI, 1.34-3.62)), macrosomia (OR, 2.93 (95% CI, 2.39-3.59)), malpresentation (OR, 2.73 (95% CI, 2.06-3.61)) and Cesarean delivery (OR, 2.31 (95% CI, 1.79-2.99)).

CONCLUSIONS

This study suggests that pregnancies complicated by idiopathic polyhydramnios are at increased risk of adverse outcome. Future investigations should aim to determine an amniotic fluid volume threshold above which antenatal fetal surveillance is appropriate in the management of these pregnancies. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Title: Is Mild Idiopathic Polyhydramnios Associated with an Increased Risk for an Intrauterine Fetal Demise? A Retrospective Cohort Study

Objective

Antenatal fetal surveillance has been recommended for moderate/severe idiopathic polyhydramnios but not for mild idiopathic polyhydramnios. The purpose of this study is to determine if pregnancies with mild idiopathic polyhydramnios have an increased risk for an intrauterine fetal demise (IUFD).

Methods

Medical records and amniotic fluid volume ultrasound data from 2016 to 2021 at a university medical center were examined. Pregnancies with fetal anomalies, fetal infection, isoimmunization, multiple gestation, maternal diabetes and oligohydramnios were excluded. Normal amniotic fluid volume was defined as an amniotic fluid index (AFI) <24 cm which was compared to mild idiopathic polyhydramnios, AFI of ≥24.0 cm-29.9 cm, and moderate/severe polyhydramnios which is an AFI ≥30 cm.

Results

Of 12,725 patients meeting inclusion study criteria, there were 249 with idiopathic polyhydramnios (n = 249) which was associated with an increased odds of IUFD (aOR) of 3.27 (CI 1.50-7.15), NICU admission (aOR 1.28, CI 0.96-1.70), 5-minute APGAR score less than 7 (aOR 2.16, CI 1.52-3.07), and large for gestational age infant (LGA) (aOR 4.04, CI 2.83-5.78) compared to normal amniotic fluid volume (AFV). In the mild polyhydramnios group (n = 204, out of the 249 women with polyhydramnios) compared to the 12,476 pregnancies with normal AFV group, IUFD (aOR 3.38, CI 1.46-7.82), NICU admission (aOR 1.19, CI 0.87-1.64), 5-minute APGAR score less than 7 (aOR 1.68, CI 1.10-2.55) and LGA (aOR 3.87, CI 2.59-5.78). In moderate/severe polyhydramnios group (n = 45) compared to the normal AFV group, there was no increased odds of IUFD (aOR 2.78, CI 0.38-20.29) or NICU admission (aOR 1.74, CI 0.93-3.26) but an increased odds for a 5-minute APGAR score less than 7 (aOR 4.94, CI 2.57-9.53) and LGA fetus (aOR 4.80, CI 2.26-10.22).

Conclusion

There is an increased odds of IUFD in pregnancies complicated by mild idiopathic polyhydramnios. Patients should be counseled on an increased odds of adverse pregnancy outcomes associated with idiopathic polyhydramnios, and in those pregnancies with mild idiopathic polyhydramnios, antenatal fetal surveillance should be considered.

Window to the Womb: Amniotic Fluid and Postnatal Outcomes

Amniotic fluid volumes are tightly regulated, and amniotic fluid derangement can indicate maternal complications or fetal abnormalities. Ultrasound estimate of amniotic fluid provides a tool to evaluate the maternal-fetal-placental interface in real-time. Oligohydramnios and polyhydramnios are associated with adverse maternal and neonatal outcomes. Oligohydramnios is associated with adverse maternal and neonatal outcomes including cesarean delivery, operative vaginal delivery, induction of labor, postpartum hemorrhage, small for gestational age neonate, intrauterine demise, neonatal death, NICU admission, and APGAR less than 7 at. 5 minutes of life Polyhydramnios is associated with adverse outcomes including cesarean delivery, induction of labor, placental abruption, shoulder dystocia, cord prolapse, postpartum hemorrhage, intrauterine fetal demise, NICU admission, neonatal death, APGAR less than 7 at 5 minutes of life, large for gestational age neonate, and respiratory distress syndrome. Therefore, Amniotic fluid should be evaluated when maternal or fetal well-being is in question.

Moderate-to-Severe Polyhydramnios: Cutoffs for Deepest Vertical Pocket Corresponding to Amniotic Fluid Index

OBJECTIVE

Society for Maternal-fetal medicine Consult Series (#46) states "antenatal fetal surveillance is not required for mild idiopathic" polyhydramnios defined as amniotic fluid index (AFI) of 24 cm or a deepest vertical pocket (DVP) between 8 and 11 cm. The objective of this study was to determine the cutoff for DVP which correlates with AFI ≥ 30 cm.

METHODS

This retrospective study of singleton third trimester ultrasounds included a study group randomly divided into test and validation. In the test group, DVP cutoffs correlating with AFI ≥ 30 cm which was used to define moderate-severe polyhydramnios were calculated in two ways, rounded to the nearest whole number: 1) a receiver operating curve and Youden's J statistic (DVP-Youden) and 2) calculation of the DVP percentile that corresponded with AFI of 30 cm (DVP-Percentile). Using the validation group, diagnostic characteristics were DVP-Youden and DVP-Percentile for diagnosis of AFI ≥ 30 cm and were compared against SMFM cutoffs (DVP-SMFM).

RESULTS

Seventy one thousand eight hundred and ninety three ultrasound exams in the 3rd trimester had assessment of AFI and DVP. Moderate-severe polyhydramnios occurred in 286 (1.2%) in test group and 571 (1.2%) in validation group. AFI of 30 cm corresponded to the 98.9th percentile, which in turn correlated to a DVP of 10 cm (DVP-Percentile). The calculated cutoff for moderate-severe polyhydramnios was 8 cm for DVP-Youden.

CONCLUSION

Using 8.0 cm rather than 12.0 cm increased the detection of moderate-severe polyhydramnios to 100% with a false positive rate under 5%. For those utilizing DVP for amniotic fluid evaluation, identification of a DVP ≥ 8.0 cm should prompt further evaluation with complete AFI.

Association and Correlation Between Amniotic Fluid Index and Glucose Concentration

Purpose: To study the association and correlation between the amniotic fluid index, random glucose concentration, and serum glucose concentration after avoiding oral intake of sugar in a pregnant female with polyhydramnios.

Methods: The research was performed on pregnant women with polyhydramnios (n=104 ) after 28 weeks. USG was performed using a SAMSUNG HS 70A (Samsung Electronics Pvt. Ltd., Seoul, South Korea) and a GE Voluson P8 (GE Healthcare, Little Chalfont, UK). We measured amniotic fluid index and took a blood sample for hemoglobin (Hb)A1C, fasting blood glucose, post-prandial and random blood glucose, and also performed a glucose tolerance test in pregnant women.

Results: This is a prospective study, all 104 patients that were recruited in this study were pregnant females with polyhydramnios mainly from the urban and rural zone with different age groups (between 21 and 37 years). In our study, we observed that after avoiding oral intake of sugar in pregnant females with polyhydramnios, it was concluded that the amnionic fluid index lies towards the lower side. Polyhydramnios is more common in the urban zone and among older pregnant females. Out of 104 pregnant females with polyhydramnios, 82 were diagnosed with gestational diabetes after 28 weeks.

Conclusion: In this study, we have concluded that the earliest and most sensitive predictor for gestational diabetes is a rise in the amniotic fluid index which could have been prevented by avoiding oral intake of sugar. Early prediction of gestational diabetes can be made by amniotic fluid index even before glucose concentration. We observed that by reducing oral intake of sugar, the amniotic fluid index drops down in pregnant females

Prenatal diagnosis of fetal growth restriction with polyhydramnios, etiology and impact on postnatal outcome

To assess the spectrum of different etiologies, the intrauterine course, outcome and possible prognostic markers in prenatally detected fetal growth restriction (FGR) combined with polyhydramnios. Retrospective study of 153 cases with FGR combined with Polyhydramnios diagnosed by prenatal ultrasound over a period of 17 years. Charts were reviewed for ultrasound findings, prenatal and postnatal outcome. All cases were categorized into etiological groups and examined for differences. Five etiological groups were identified: chromosomal anomalies (n = 64, 41.8%), complex malformation syndromes (n = 37, 24.1%), isolated malformations (n = 24, 15.7%), musculoskeletal disorders (n = 14, 9.2%) and prenatal non-anomalous fetuses (n = 14, 9.2%). Subgroups showed significant disparities in initial diagnosis of combination of both pathologies, Ratio AFI/ gestational weeks and Doppler ultrasound examinations. Overall mortality rate was 64.7%. Fetuses prenatally assigned to be non-anomalous, showed further complications in 42.9% (n = 6). Fetuses prenatally diagnosed with FGR combined with polyhydramnios are affected by a high morbidity and mortality. Five etiologic groups can be differentiated, showing significant disparities in prenatal and postnatal outcome. Even without recognizable patterns prenatally, long-term-follow up is necessary, as neurodevelopmental or growth delay may occur.

Amniotic Aaquaporins (AQP) in Normal and Pathological Pregnancies: Interest in Polyhydramnios

Polyhydramnios is a common feature diagnosed by ultrasound in the second half of pregnancy. Biochemical analysis of amniotic fluid can be useful when suspecting Bartter syndrome or digestive atresia but in most of cases, no etiology of polyhydramnios is found because of the complex regulation of amniotic fluid. Aquaporins (AQP) are transmembrane channel proteins contributing to water transfers. Some of them are expressed in fetal membranes and placenta. Their expression has been shown to be disrupted in some pathological conditions such as maternal diabetes, often associated with polyhydramnios. AQP-1, 3 and 8 levels in amniotic fluid were retrospectively measured in patients suffering from polyhydramnios (n=21) from 23 weeks of gestation (WG). They were compared to the levels observed in control subjects (n=96) and their relationship with maternal factors and neonatal issues was analyzed. AQP-1, 3, 8 levels were physiologically fluctuating, AQP-1 levels always being the lowest and AQP-3 the highest, with a significant decrease at the end of pregnancy. AQPs/AFP ratios increased about 8 folds during pregnancy, their kinetic profiles reflecting physiological dynamic evolution of amniotic fluid volume. In polyhydramnios, AQP-3 level tended to be decreased whereas AQP-8 level was decreased from mid-gestation whatever the etiology of polyhydramnios. No significant relationship was found between AQPs levels and either the fetal prematurity degree or macrosomia. No specific pattern was observed in idiopathic polyhydramnios, limiting the interest of AQPs dosage in amniotic fluid in the management of those complicated pregnancies.

Fetal endoscopic tracheal occlusion reverses the natural history of right-sided congenital diaphragmatic hernia: European multicenter experience

OBJECTIVE

To evaluate the neonatal outcome of fetuses with isolated right-sided congenital diaphragmatic hernia (iRCDH) based on prenatal severity indicators and antenatal management.

METHODS

This was a retrospective review of prospectively collected data on consecutive cases diagnosed with iRCDH before 30 weeks' gestation in four fetal therapy centers, between January 2008 and December 2018. Data on prenatal severity assessment, antenatal management and perinatal outcome were retrieved. Univariate and multivariate logistic regression analysis were used to identify predictors of survival at discharge and early neonatal morbidity.

RESULTS

Of 265 patients assessed during the study period, we excluded 40 (15%) who underwent termination of pregnancy, two cases of unexplained fetal death, two that were lost to follow-up, one for which antenatal assessment of lung hypoplasia was not available and six cases which were found to have major associated anomalies or syndromes after birth. Of the 214 fetuses with iRCDH included in the neonatal outcome analysis, 86 were managed expectantly during pregnancy and 128 underwent fetal endoscopic tracheal occlusion (FETO) with a balloon. In the expectant-management group, lung size measured by ultrasound or by magnetic resonance imaging was the only independent predictor of survival (observed-to-expected lung-to-head ratio (o/e-LHR) odds ratio (OR), 1.06 (95% CI, 1.02-1.11); P = 0.003). Until now, stratification for severe lung hypoplasia has been based on an o/e-LHR cut-off of 45%. In cases managed expectantly, the survival rate was 15% (4/27) in those with o/e-LHR ≤ 45% and 61% (36/59) for o/e-LHR > 45% (P = 0.001). However, the best o/e-LHR cut-off for the prediction of survival at discharge was 50%, with a sensitivity of 78% and specificity of 72%. In the expectantly managed group, survivors with severe pulmonary hypoplasia stayed longer in the neonatal intensive care unit than did those with mildly hypoplastic lungs. In fetuses with an o/e-LHR ≤ 45% treated with FETO, survival rate was higher than in those with similar lung size managed expectantly (49/120 (41%) vs 4/27 (15%); P = 0.014), despite higher prematurity rates (gestational age at birth: 34.4 ± 2.7 weeks vs 36.8 ± 3.0 weeks; P < 0.0001). In fetuses treated with FETO, gestational age at birth was the only predictor of survival (OR, 1.25 (95% CI, 1.04-1.50); P = 0.02).

CONCLUSIONS

Antenatal measurement of lung size can predict survival in iRCDH. In fetuses with severe lung hypoplasia, FETO was associated with a significant increase in survival without an associated increase in neonatal morbidity. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Performance of diagnostic ultrasound to identify causes of hydramnios

INTRODUCTION

We aimed to assess the diagnostic yield of ultrasonography in the identification of the etiology of hydramnios, and the added value of MRI or amniocentesis.

METHODS

We conducted a single-center retrospective study including pregnancies with confirmed hydramnios (defined as deepest pocket ≥8 cm) between January 2013 and May 2017. Twin pregnancies, secondary hydramnios discovered after the diagnosis of a causal pathology, and pregnancies of unknown outcome were excluded. All pregnancies underwent a targeted scan, and selected cases underwent MRI or amniocentesis.

RESULTS

A total of 158 patients with confirmed hydramnios were included. Hydramnios was associated with a fetal pathology in 37 cases (23.4%), with diabetes in 39 (24.6%), isolated macrosomia in 16 (10.1%), and considered idiopathic in 66 (41.7%). Ultrasonography established a diagnosis of the underlying pathology in 73% of cases. Amniocentesis was done in 31 cases (20%) and it allowed diagnosis of chromosome anomalies, esophageal atresia, myotonic dystrophy congenital type, Prader-Willi syndrome, and Bartter syndrome. MRI was done in 15 cases (10%) and it allowed one additional diagnosis of esophageal atresia. The diagnostic yields of MRI and amniocentesis were 91.7% and 95.2%, respectively. There were five false positive diagnoses at ultrasonography, and one false positive diagnosis at MRI.

CONCLUSION

Hydramnios can be associated with a wide variety of underlying pathologies. Diagnostic ultrasound can attain a diagnosis in the majority of cases. Amniocentesis offers a valuable complementary assessment.

[Postnatal outcome from polyhydramnios without sonographic abnormalities]

OBJECTIVES

To assess adverse outcome of polyhydramnios without morphological abnormalities and to determine the factors associated with an adverse outcome.

METHODS

This is a retrospective observational cohort study conducted in a French tertiary care unit between 2008 and 2018 including all women with singleton pregnancy complicated by polyhydramnios. Presence of morphological abnormality was an exclusion criteria. The primary outcome was the rate of adverse outcome, defined by a composite criterion including death or postnatal discovery of malformation or chronic pathology. Maternal, obstetrical, paediatric and polyhydramnios characteristics were collected.

RESULTS

Ninety-one women with polyhydramnios were included. The rate of adverse outcome was 24.2% (22/91). This rate was 20,3% in case of idiopathic polyhydramnios and 33,3% in case of maternal diabetes associated. The postnatal mortality rate was 5.5%. The rate of malformations not diagnosed in antenatal was 11%. Obesity (50% vs. 18,8%; P=0,004), early diagnosis (72,7% before 32 WG vs. 44,9%; P=0,02), and severity of polyhydramnios (22,7% vs. 4,3% in severe polyhydramnios; P=0,01) were associated significantly with an adverse outcome. In these cases, the incidence of preterm delivery was higher.

CONCLUSION

Polyhydramnios must have second-line ultrasound, including isolated maternal diabetes. A systematic genetic assessment can be discussed.

SMFM Consult Series #46: Evaluation and management of polyhydramnios

Polyhydramnios, or hydramnios, is an abnormal increase in the volume of amniotic fluid. Identification of polyhydramnios should prompt a search for an underlying etiology. Although most cases of mild polyhydramnios are idiopathic, the 2 most common pathologic causes are maternal diabetes mellitus and fetal anomalies, some of which are associated with genetic syndromes. Other causes of polyhydramnios include congenital infection and alloimmunization. The purpose of this document is to provide guidance on the evaluation and management of polyhydramnios. The following are Society for Maternal-Fetal Medicine recommendations: (1) we suggest that polyhydramnios in singleton pregnancies be defined as either a deepest vertical pocket of ≥8 cm or an amniotic fluid index of ≥24 cm (GRADE 2C); (2) we recommend that amnioreduction be considered only for the indication of severe maternal discomfort, dyspnea, or both in the setting of severe polyhydramnios (GRADE 1C); (3) we recommend that indomethacin should not be used for the sole purpose of decreasing amniotic fluid in the setting of polyhydramnios (GRADE 1B); (4) we suggest that antenatal fetal surveillance is not required for the sole indication of mild idiopathic polyhydramnios (GRADE 2C); (5) we recommend that labor should be allowed to occur spontaneously at term for women with mild idiopathic polyhydramnios; that induction, if planned, should not occur at <39 weeks of gestation in the absence of other indications; and that mode of delivery should be determined based on usual obstetric indications (GRADE 1C); and (6) we recommend that women with severe polyhydramnios deliver at a tertiary center due to the significant possibility that fetal anomalies may be present (GRADE 1C).

Association between amniotic fluid evaluation and fetal biometry: a prospective French "Flash" study

We aimed to study the association between three different methods of assessing the amount of amniotic fluid (subjective method (SM), deepest vertical pocket (DVP) and amniotic fluid index (AFI)) and estimated fetal weight (EFW) (in percentile or Z-score) after adjustment on maternal-fetal parameters. We performed a nationwide cross-sectional study through the French network of obstetric sonographers using the "flash" study method and including low-risk singleton pregnancies from 18-40 weeks. Crude and adjusted odds ratio were computed after stratification upon 2nd and 3rd trimester of pregnancy. 1667 ultrasound scans performed by 65 operators were included. Only Z-score of EFW was significantly associated with SM in both trimesters. For DVP and AFI, Z-score of EFW and male fetal gender was significantly associated with them in 2nd trimester. In the 3rd trimester, both Z-score of EFW and large (LGA) or small for gestational age (SGA) fetus were significantly associated with AFI. and DVP. Overweight woman and class I obesity women were also significantly associated with DVP modification. In conclusion, all three methods of amniotic fluid evaluation are significantly associated to estimated fetal weight. DVP and AFI appeared equivalent except that maternal-fetal factors seemed to have a higher impact in DVP than AFI.

Polyhydramnios or Excessive Fetal Growth Are Markers for Abnormal Perinatal Outcome in Euglycemic Pregnancies

OBJECTIVE

 This study aims to investigate the perinatal outcome of fetuses with polyhydramnios and/or accelerated growth among women with a normal oral glucose challenge test (oGCT).

METHODS

 Singleton, nonanomalous pregnancies with an oGCT(< 130 mg/dL) at 24 to 28 weeks, who subsequently demonstrate polyhydramnios (amniotic fluid index > 24 cm or maximum vertical pocket > 8 cm) and/or accelerated growth (abdominal circumference > 95th percentile) on two-third trimester examinations were studied. Maternal demographics, delivery, and neonatal information were recorded. Cases were compared with a reference group (normal oGCT with neither abnormal third-trimester growth nor polyhydramnios).

RESULTS

 A total of 282 pregnancies were in the study group, and 663 were in the reference group. Deliveries in the study group were at a higher risk for birth weight (BW)% > 90%, standard deviation, and postpartum hemorrhage when compared with the reference group (adjusted odds ratio: 2.3-5.6). Pregnancies complicated by both polyhydramnios and accelerated fetal growth were significantly more likely to result in a BW% > 90% (odds ratio [OR]: 18.5; 95% confidence interval [CI]: 8.9-38.6) and PPH (OR: 4.2; 95% CI: 2.4-7.6).

CONCLUSION

 Pregnancies with normal oGCT that develop polyhydramnios and accelerated growth are at higher risk for maternal and neonatal complications. Isolated polyhydramnios without accelerated growth increases the risk for delivery complications but not neonatal morbidity.

Association between cord blood cystatin C levels and early mortality of neonates with congenital abnormalities of the kidney and urinary tract: a single-center, retrospective cohort study

BACKGROUND

Some fetuses with congenital abnormalities of the kidney and urinary tract (CAKUT) have severe renal dysfunction during the prenatal period that can result in oligohydramnios, pulmonary hypoplasia, and death following birth. We hypothesized that cord blood cystatin C (CysC) levels are elevated in neonates who have life-threatening pulmonary hypoplasia and oligohydramnios due to severe renal dysfunction. In this study we compared cord blood CysC levels between a non-survivor group with CAKUT and a survivor group.

METHODS

This was a single-center, retrospective cohort study conducted between January 2007 and December 2015. Eighty-seven neonates who were prenatally diagnosed with CAKUT were included in the study. Cord blood CysC and creatinine levels were compared between the survivor and non-survivor groups at discharge from hospital.

RESULTS

Of the 87 neonates enrolled in the study, 67 survived and 21 died before discharge. Median cord blood CysC levels were higher in the non-survivor group than in the survivor group (4.28 vs. 1.96 mg/L, respectively; p < 0.001). Cord blood creatinine levels were not significantly different between the two groups. In patients with oligohydramnios (n = 28), cord blood CysC levels were significantly higher in the non-survivor group than in the survivor group (4.28 vs. 2.23 mg/L, respectively; p = 0.002).

CONCLUSIONS

In this study population, cord blood CysC levels were significantly higher in the non-survivor group with CAKUT than in the survivor group. These results suggest that cord blood CysC levels may be a good marker of the severity of renal dysfunction at birth.

Outcome of pregnancy in women diagnosed with idiopathic polyhydramnios

INTRODUCTION

Polyhydramnios is present in approximately 2% of pregnancies and it has been associated with a variety of adverse pregnancy outcomes.

OBJECTIVES

The aim of our study was to evaluate the association between polyhydramnios and adverse pregnancy outcomes.

METHODS

This was a retrospective case control study of 288 singleton pregnancies delivered in the Rotunda Hospital, Dublin, between 2013 and 2014. Polyhydramnios was defined as: (i) amniotic fluid index (AFI) ≥ 25 cm; (ii) maximal vertical pocket (MVP) of ≥8 cm; and (iii) a gestational age-specific threshold for AFI. Demographic information, obstetric and neonatal outcomes were obtained by review of hospital databases. Exclusion criteria included gestational or pre-existing diabetes, multiple pregnancy, carrying a fetus with structural or chromosomal abnormalities, Rhesus factor isoimmunisation, and TORCH screen positive. Outcomes were compared with outcomes of those without polyhydramnios.

RESULTS

A total of 8798 deliveries occurred during the study period. The frequency of polyhydramnios was 1.6%. One hundred and forty-four women were selected in each group. There was no significant difference in preterm deliveries, low birth weight, low Apgar score at one minute and five minutes and perinatal mortality. However, increase in caesarean delivery rate (43.1% vs 21.5%), number of fetal distresses (17.4% vs 6.9%) and number of neonatal intensive care unit (NICU) admissions (17.4% vs 4.9%) were observed in our study.

CONCLUSION

In conclusion, idiopathic polyhydramnios is associated with specific adverse outcomes, such as higher rate of caesarean delivery, fetal distress and NICU admissions. Therefore, close surveillance of these pregnancies is required, especially near term.

Mode of delivery among women admitted with polyhydramnios

A retrospective matched case control study was conducted to examine the incidence of caesarean delivery (CD) among women admitted with polyhydramnios with and without a trial of labour compared to women with normal amniotic fluid index (AFI). Singleton pregnancies diagnosed with polyhydramnios upon admission to labour between 2003 and 2013 were included. A control group (normal AFI) matched at a ratio of 1:1 was randomly selected. Primary outcome was the incidence of CD. A total of 588 women were included. The overall incidence of CD was significantly higher among women with polyhydramnios (31.3%) compared to the controls (18.7%), (p < .001). The incidences of both non-labouring caesarean and intrapartum operative deliveries were significantly higher among women with polyhydramnios compared to the controls (p = .007 and p = .01, respectively). On a multiple logistic regression model, polyhydramnios was found to be an independent risk factor for delivery by a caesarean (p = .0015; OR 2.0; 95%CI 1.30-2.90).

Antenatal fetal surveillance "Assessment of the AFV"

The evaluation of amniotic fluid volume (AFV) is an established part of the antenatal surveillance of pregnancies at risk for an adverse pregnancy outcome. The two most commonly used ultrasound techniques to estimate AFV are the amniotic fluid index (AFI) and the single deepest pocket (SDP). Four studies have defined normal AFVs, and although their normal volumes have similarities, there are also differences primarily due to the statistical methodology used in each study. Dye-determined AFV correlates with ultrasound estimates for normal fluid volumes but correlates poorly for oligohydramnios and polyhydramnios. The addition of color Doppler in estimating AFV leads to the overdiagnosis of oligohydramnios. Neither the AFI nor the SDP is superior in identifying oligohydramnios, but the SDP is a better measurement choice as the use of AFI increases the diagnosis rate of oligohydramnios and labor inductions without an improvement in pregnancy outcomes.

Severe antenatally diagnosed renal disorders: background, prognosis and practical approach

Nowadays most renal disorders, especially urinary tract malformations and renal cystic disease, are diagnosed antenatally. In cases of severe bilateral disease, intrauterine renal dysfunction may lead to renal oligohydramnios (ROH), resulting in pulmonary hypoplasia which affects perinatal mortality and morbidity as well as the long-term outcome. However, some infants may only have mild pulmonary and renal disease, and advances in postnatal and dialysis treatment have resulted in improved short- and long-term outcome even in those infants with severe ROH. Here, we review the current state of knowledge and clinical experience of patients presenting antenatally with severe bilateral renal disorders and ROH. By addressing underlying mechanisms, intrauterine tools of diagnosis and treatment as well as published outcome data, we hope to improve antenatal counselling and postnatal care. KEY SUMMARY POINTS: 1. Nowadays most renal disorders are diagnosed antenatally, especially urinary tract malformations and renal cystic disease. 2. Severe kidney dysfunction may lead to renal oligohydramnios, which can cause pulmonary hypoplasia and is a risk factor of perinatal mortality and postnatal renal outcome. However, as considerable clinical heterogeneity is present, outcome predictions need to be treated with caution. 3. Advances in postnatal and dialysis treatment have resulted in improved short- and long-term outcomes even in infants with severe renal oligohydramnios. 4. A multidisciplinary approach with specialist input is required when counselling a family with an ROH-affected fetus as the decision-making process is very challenging.

Amniotic fluid as a vital sign for fetal wellbeing

Introduction: Amniotic fluid, once thought to merely provide protection and room for necessary movement and growth for the fetus, is now understood to be a highly complex and dynamic system that is studied as a data point to interpret fetal wellbeing.

Methods: Assessment of amniotic fluid volume is now routine when performing a sonographic evaluation of fetal status and is an important consideration in the assessment and management of perinatal morbidity and mortality.^1,2 In this review, we will cover the dynamics that affect amniotic fluid volume, review methods for measurement and quantification of volume, review definitions for normative data as related to neonatal outcomes, and provide evidence based guidance on the workup and management options for oligoydramnios and polyhydramnios in singleton and twin pregnancies. Conclusions: When abnormalities of fluid exist, appropriate workup to uncover the underlying etiology should be initiated as adverse fetal outcomes are sometimes associated with these variations from normalcy.

Association of isolated polyhydramnios at or beyond 34 weeks of gestation and pregnancy outcome. Obstet Gynecol. 2015;125:825-832. [PMID: 25751210 DOI: 10.1097/aog.0000000000000740]

OBJECTIVE

To evaluate pregnancy outcome among women with isolated polyhydramnios at admission for labor at or beyond 34 weeks of gestation.

METHODS

Retrospective cohort study at a tertiary medical center between 2007 and 2012. Isolated polyhydramnios was defined as amniotic fluid index (AFI) greater than 25 cm at admission in the absence of gestational or pregestational diabetes mellitus or fetal structural or chromosomal anomalies. Women with isolated polyhydramnios were compared with women with a normal AFI (5-25 cm).

RESULTS

Overall, 31,376 women were eligible for analysis, of whom 215 (0.7%) had isolated polyhydramnios and 31,161 normal AFI. Women with isolated polyhydramnios had higher rates of labor induction (7.9% compared with 4.8%, P=.04) and cesarean delivery (12.1% compared with 5.1%, P<.001). They also had higher rates of placental abruption (0.9% compared with 0.2%, P=.02), abnormal or intermediate fetal heart rate (FHR) tracings (7.0% compared with 3.2%, P=.002), and prolonged first stage of delivery (6.0% compared with 1.4%, P<.001). Isolated polyhydramnios was also associated with higher rates of shoulder dystocia (1.9% compared with 0.3%, P<.001) and respiratory distress syndrome (0.5% compared with 0.03%, P=.001). On a multiple logistic regression model, isolated polyhydramnios was an independent risk factor for labor induction (adjusted odds ratio [OR] 1.7, 95% confidence interval [CI] 1.01-2.8), cesarean delivery (adjusted OR 2.6, 95% CI 1.7-4.0), prolonged first stage of delivery (adjusted OR 3.6, 95% CI 1.97-6.7), abnormal or intermediate FHR tracings (adjusted OR 2.6, 95% CI 1.6-4.5), placental abruption (adjusted OR 8.4, 95% CI 2.00-35.4), shoulder dystocia (adjusted OR 3.4, 95% CI 1.2-9.7), and respiratory distress syndrome (adjusted OR 38.9, 95% CI 4.6-332.6). Mild isolated polyhydramnios (AFI 25.1-30.0) was independently associated with cesarean delivery, prolonged first stage of delivery, placental abruption, abnormal or intermediate FHR tracings, and shoulder dystocia.

CONCLUSION

Isolated polyhydramnios at admission for labor at or beyond 34 weeks of gestation is associated with adverse obstetric and neonatal outcomes.

Does the level of amniotic fluid have an effect on the accuracy of sonographic estimated fetal weight at term?

OBJECTIVE

Controversy exists concerning the impact of amniotic fluid index (AFI) on the accuracy of sonographic estimation of fetal weight (EFW). Thus, we aimed to evaluate whether differences in AFI has an influence on the accuracy of sonographic EFW.

METHODS

All term, singleton pregnancies which underwent a sonographic EFW and measurement of AFI within a week from delivery were included. Cases were stratified into three categories according to AFI: (1) Normal AFI (51-249 mm), (2) Oligohydramnios (AFI ≤ 50 mm) and (3) Polyhydramnios (AFI ≥ 250 mm). Inaccurate EFW was defined if there was more than 15% difference between sonographic EFW and actual birthweight.

RESULTS

Overall, 1746 pregnancies were identified (1096 with normal AFI, 455 with oligohydramnios and 195 with polyhydramnios). Mean AFI was 115.8 ± 60 mm, 28.1 ± 13 mm and 293 ± 35 mm, p < 0.001, and mean sonographic EFW was 3182.5 ± 573 g, 3118.8 ± 517 g and 3713.2 ± 461 g, p < 0.001, respectively. Demographic data and gestational age at delivery were similar. Mean birthweight was 3221.7 ± 535 g, 3132.5 ± 505 g and 3654.1 ± 480 g, p < 0.001, respectively. The rate of inaccurate EFW was similar between the groups (8.4%, 8.7% and 9.7%, p = 0.19, respectively). On multivariate analysis, AFI was not associated with EFW inaccuracy (OR 1.01, 95% C.I 0.67-1.54, p = 0.93).

CONCLUSION

AFI has limited impact on the percentage of errors in sonographic fetal weight estimation a week prior delivery.

Diagnosis, evaluation, and management of the hypertensive disorders of pregnancy

OBJECTIVE

This guideline summarizes the quality of the evidence to date and provides a reasonable approach to the diagnosis, evaluation and treatment of the hypertensive disorders of pregnancy (HDP).

EVIDENCE

The literature reviewed included the previous Society of Obstetricians and Gynaecologists of Canada (SOGC) HDP guidelines from 2008 and their reference lists, and an update from 2006. Medline, Cochrane Database of Systematic Reviews (CDSR), Cochrane Central Registry of Controlled Trials (CCRCT) and Database of Abstracts and Reviews of Effects (DARE) were searched for literature published between January 2006 and March 2012. Articles were restricted to those published in French or English. Recommendations were evaluated using the criteria of the Canadian Task Force on Preventive Health Care and GRADE.

Dialysis for twins

A 32-year-old woman with known stage-4 chronic kidney disease due to lupus nephritis presented with twin pregnancy after in vitro fertilization at a gestational age of 24 weeks + 3 days because of imminent preterm labour. Repeated ultrasound evaluations confirmed intrauterine growth restriction in both twins and polyhydramnios as the cause of imminent preterm labour. After initiation of haemodialysis treatment, ultrasound evaluation showed a significant decrease in amniotic fluids, and also reduction in blood urea nitrogen and in clinical complaints could be observed. At a gestational age of 28 weeks + 4 days, delivery was performed by Caesarean section. This case study shows that effective treatment of elevated uraemic toxins significantly reduced the morbidity risks of the twins.

Toward consistent terminology: assessment and reporting of amniotic fluid volume

Amniotic fluid is typically measured by ultrasound using the amniotic fluid index (AFI) or the maximum vertical pocket (MVP). Although both parameters correlate poorly with the actual amniotic fluid volume measured with dye-dilution methods, cross-sectional studies have been used to establish gestational norms. The current acceptable definition of polyhydramnios in the late second and the third trimester in both singleton and multiple gestations is a MVP > 8 cm, while the definition of oligohydramnios is a MVP < 2 cm. The pocket to be measured should exclude the umbilical cord or fetal parts. Randomized clinical trials have indicated that defining oligohydramnios as a MVP < 2 cm will result in fewer obstetrical interventions and similar perinatal outcomes when compared to an AFI < 5 cm.

Polyhydramnios as a predictor of adverse pregnancy outcomes

OBJECTIVES

This study aimed to ascertain the frequency of polyhydramnios in singleton pregnancies, to determine the associated risk factors, and assess the adverse maternal and perinatal outcomes.

METHODS

A retrospective cohort study of all singleton pregnancies complicated with polyhydramnios after 28 weeks of gestation was carried out in Nizwa Hospital's Obstetrics & Gynecology Department, Oman, from January 2002 to December 2007. Of 25,979 pregnant women reviewed, 477 were found to have polyhydramnios. The control group consisted of 900 pregnant women. Cases of polyhydramnios were diagnosed as mild, moderate, or severe based on their highest amniotic fluid index. Cases were compared with controls in terms of demographic data; prevalence of diabetes, macrosomia, or Caesarean deliveries; frequency of fetal anomalies, and perinatal mortality rate.

RESULTS

Polyhydramnios was diagnosed in 1.8% of pregnancies. It was mild in 382 (80%), moderate in 84 (17.6%), and severe in 12 (2.4%). A total of 72 (15.3 %) cases of polyhydramnios were complicated by diabetes (gestational or established diabetes mellitus) as compared to 10% of the control group and 39 (8.1%) neonates had congenital anomalies. Polyhydramnios was associated with advanced maternal age; 58 (12.2%) of subjects were over 40 years old. The perinatal mortality rate with polyhydramnios was 42 per 1,000 births compared to 14 per 1000 births in the control group.

CONCLUSION

These data demonstrate that polyhydramnios is associated with an increased risk of adverse perinatal outcomes, and there is a significant positive relation with maternal age, diabetes, fetal anomalies, and fetal macrosomia.

Polyhydramnios: a warning sign in the prenatal ultrasound diagnosis of foetal malformation? Diagn Interv Imaging. 2013;94:433-437. [PMID: 23403339 DOI: 10.1016/j.diii.2013.01.002]

PURPOSE

To propose polyhydramnios seen during prenatal diagnosis as a warning sign of foetal malformation.

PATIENTS AND METHODS

A retrospective multicentre study over a three-year period carried out in Ivory Coast and Burkina Faso. We reviewed 3903 obstetric ultrasound reports. All cases of foetal malformation and polyhydramnios were counted. The instances of foetal malformation associated with polyhydramnios were compared to those of foetal malformation without polyhydramnios and to polyhydramnios only.

RESULTS

A list of 72 cases of polyhydramnios was made (equating to 1.8%). In 55 cases (76.4%), polyhydramnios was combined with foetal malformation. These were lethal abnormalities in 33 cases and non-lethal in 22 cases. In 17 cases, polyhydramnios was not associated with any foetal malformations and in eight cases, foetal malformation was discovered in the absence of polyhydramnios. Polyhydramnios had a positive predictive value of 76.4% for the presence of foetal malformation. The negative predictive value was 99.8%. Sensitivity was 87.3% and specificity was 99.5%.

CONCLUSION

Polyhydramnios is a highly sensitive and specific sign for prenatal diagnosis of foetal malformation. If it is identified, then this should lead to a very careful search for foetal malformation.

Prognosis and outcome of pregnancies exposed to renin-angiotensin system blockers

OBJECTIVE

To study pregnancy outcomes and fetal renal prognosis markers in cases of exposure to renin-angiotensin system blockers.

METHODS

We conducted a retrospective study of a series of 21 patients exposed to blockers of the renin-angiotensin system during pregnancy. Two markers were prenatally studied, fetal serum β2-microglobulin and amniotic fluid volume. Poor renal prognosis evaluation was based on postnatal glomerular filtration rate or on the presence of renal histologic lesions.

RESULTS

Of the 21 fetuses, only one had a normal postnatal renal function at birth (oligohydramnios regression and normal β2-microglobulin). All fetuses with persistent oligohydramnios or β2-microglobulin ≥ 5 mg/L presented an adverse renal outcome.

CONCLUSION

Exposure to renin-angiotensin system blockers complicated by oligohydramnios is associated with a very poor outcome. We propose a prenatal management based on amniotic fluid volume monitoring and fetal serum β2-microglobulin. However, our preliminary results have to be confirmed by a larger study.

Maximal amniotic fluid index as a prognostic factor in pregnancies complicated by polyhydramnios

OBJECTIVES

Polyhydramnios is present in approximately 2% of pregnancies and has been associated with a variety of adverse pregnancy outcomes. Our aim was to evaluate the association between the maximal amniotic fluid index (AFI) and the frequency of specific adverse outcomes.

METHODS

This was a retrospective chart review of 524 singleton pregnancies diagnosed with polyhydramnios and delivered in a single tertiary referral center between 2003 and 2008. Polyhydramnios was defined as either AFI ≥ 25 cm or a maximum vertical pocket (MVP) ≥ 8 cm even in the presence of AFI < 25 cm. The cohort was stratified into four groups based on the maximal AFI noted during the pregnancy: < 25 cm but with MVP ≥ 8 cm; 25-29.9 cm; 30-34.9 cm; and ≥ 35 cm. Data were collected to determine the frequency of the following adverse pregnancy outcomes: prenatally diagnosed congenital anomalies, fetal aneuploidy, preterm delivery, Cesarean delivery, low birth weight, 5-min Apgar score < 7 and perinatal mortality.

RESULTS

Higher AFI was associated with a statistically significant increase in the frequency of adverse pregnancy outcomes. The most severe form of polyhydramnios, as based on the maximal AFI (≥ 35 cm; n = 67), was associated with the highest rates of prenatally diagnosed congenital anomalies (79%), preterm delivery (46%), small-for-gestational-age neonate (16%), aneuploidy (13%) and perinatal mortality (27%). No significant association between degree of polyhydramnios and adverse outcome was demonstrated in cases of idiopathic polyhydramnios (n = 253).

CONCLUSIONS

There is an association between the frequencies of a variety of adverse pregnancy outcomes and the severity of polyhydramnios as reflected by the maximal AFI.

Amniotic fluid and the clinical relevance of the sonographically estimated amniotic fluid volume: oligohydramnios

The amniotic fluid volume (AFV) is regulated by several systems, including the in-tramembranous pathway, fetal production (fetal urine and lung fluid) and uptake (fetal swallowing), and the balance of fluid movement via osmotic gradients. The normal AFV across gestation has not been clearly defined; consequently, abnormal volumes are also poorly defined. Actual AFVs can be measured by dye dilution techniques and directly measured at cesarean delivery; however, these techniques are time-consuming, are invasive, and require laboratory support, and direct measurement can only be done at cesarean delivery. As a result of these limitations, the AFV is estimated by the amniotic fluid index (AFI), the single deepest pocket, and subjective assessment of the AFV. Unfortunately, sonographic estimates of the AFV correlate poorly with dye-determined or directly measured amniotic fluid. The recent use of color Doppler sonography has not improved the diagnostic accuracy of sonographic estimates of the AFV but instead has led to overdiagnosis of oligohydramnios. The relationship between the fixed cutoffs of an AFI of 5 cm or less and a single deepest pocket of 2 cm or less for identifying adverse pregnancy outcomes is uncertain. The use of the single deepest pocket compared to the AFI to identify oligohydramnios in at-risk pregnancies seems to be a better choice because the use of the AFI leads to an increase in the diagnosis of oligohydramnios, resulting in more labor inductions and cesarean deliveries without any improvement in peripartum outcomes.

The role of amniotic fluid assessment in indicated preterm delivery

Measuring amniotic fluid pockets with ultrasound is an efficient and reasonably reliable method of evaluating amniotic fluid volume and categorizing relative risk of perinatal morbidity. The most commonly used ultrasound criteria for oligohydramnios, SDP <2 cm and AFI <5 cm, assign approximately 2%-3% and 4%-5% of late preterm pregnancies into the "low amniotic fluid" category. The AFI offers somewhat greater sensitivity and greater precision but has less specificity for predicting perinatal morbidity than does the SDP. Thus, before 34 weeks, use of the AFI <5 cm as a criterion for intensive fetal monitoring, but not as sole criteria for delivery, is recommended. In pregnancies beyond 34 weeks, use of either AFI or SDP to diagnose oligohydramnios can be expected to reliably identify fetuses at risk for compromised perinatal outcome especially if replicate measurements are confirmatory. In such cases, care must be taken to identify comorbid conditions that, together with oligohydramnios, may place the fetus at significant risk. In such cases, delivery is the recommended intervention.

The role of amniotic fluid assessment in evaluating fetal well-being

Owing to the frequent use of bedside ultrasound, much is known about the regulation of and normative values for amniotic fluid volume and the mechanisms by which this fluid is regulated. The management protocols for conditions with extremes of amniotic fluid volume have become more exact, resulting in interventions more likely to improve outcome. Much is still unclear; there are no tools to measure amniotic fluid volume with precision, and measurement of fetal urinary output is cumbersome and error-prone.

Ultrasound predictors of mortality in monochorionic twins with selective intrauterine growth restriction

OBJECTIVES

The aim of this study was to evaluate the use of ultrasound assessment to predict risk of mortality in expectantly managed monochorionic twin fetuses with selective intrauterine growth restriction (sIUGR).

METHODS

This was a retrospective study of 101 monochorionic twin pregnancies diagnosed with sIUGR before 26 weeks of gestation. All patients were under expectant management during the observation period. At the initial evaluation, the presence or absence of each of the following abnormalities was documented: oligohydramnios; stuck twin phenomenon; severe IUGR < 3(rd) centile of estimated fetal weight; abnormal Doppler in the umbilical artery; and polyhydramnios in the larger twin. The relationships between these ultrasound findings and mortality of sIUGR fetuses were evaluated using multiple logistic regression analysis.

RESULTS

Of 101 sIUGR twins, 22 (21.8%) fetuses suffered intrauterine demise and nine (8.9%) suffered neonatal death; 70 (69.3%) survived the neonatal period. Multiple logistic regression analysis revealed that the stuck twin phenomenon (odds ratio (OR): 14.5; 95% CI: 2.2-93.2; P = 0.006) and constantly absent diastolic flow in the umbilical artery (OR: 29.4; 95% CI: 3.3-264.0; P = 0.003) were significant risk factors for mortality.

CONCLUSIONS

Not only abnormal Doppler flow in the umbilical artery but also severe oligohydramnios should be recognized as important indicators for mortality in monochorionic twins with sIUGR.

Differences in amniotic fluid patterns and fetal biometric parameters in third trimester pregnancies with and without diabetes

OBJECTIVE

The amniotic fluid index (AFI) has been increasingly used in the assessment of fetal well-being. We conducted the study to evaluate and compare the amniotic fluid index in third trimester normal and diabetic human pregnancy and to assess the correlation between the AFI and the fetal biometric parameters.

METHODS

Real-time ultrasound was performed to evaluate the AFI (four-quadrant technique), and to measure the biparietal diameter, head circumference, abdominal circumference, and femur length in 225 normal and 120 diabetic pregnant women from 27 to 42 weeks of gestation. Each patient was studied only once.

RESULTS

AFI in normal pregnancies was less than that in diabetic pregnancies throughout the gestational ages studied (27-42 weeks). In normal pregnancy, the mean AFI was 14.0 cm at 27 weeks and decreased to 11.4 cm at 42 weeks (r = 0.25, p = 0.0005), whereas in diabetic pregnancies, the values remained stable throughout the gestational ages studied. There exist significant differences in AFI, estimated fetal weight, estimated fetal weight %, abdominal circumference, abdominal circumference %, and head circumference to abdominal circumference ratio between the two groups. In both normal and diabetic pregnancies, there is a positive correlation between the AFI and the percentile of abdominal circumference (p < 0.0001), and between the AFI and the percentile of estimated fetal weight (p < 0.0001).

CONCLUSION

This study provides gestational age-specific values of the AFI in normal and diabetic pregnancies. Diabetic pregnancy has greater AFI values than normal pregnancy between 27 and 42 weeks. The AFI correlates to the percentile of the estimated fetal weight and the abdominal circumference in both groups, suggesting that there may be a relationship between increased AFI and large for gestational age fetus independent of diabetes.

Responses of amniotic fluid volume and its four major flows to lung liquid diversion and amniotic infusion in the ovine fetus

We designed experiments to allow direct measurement of amniotic fluid volume and continuous measurement of lung liquid production, swallowing, and urine production in fetal sheep. From these values, the rate of intramembranous absorption was calculated. Using this experimental design, the contribution of lung liquid to the control of amniotic fluid volume was examined. Fetuses were assigned to 1 of 4 protocols, each protocol lasting 3 days: control, isovolemic replacement of lung liquid, supplementation of amniotic fluid inflow by 4 L/day, and supplementation of amniotic inflow during isovolemic replacement of lung liquid. We found no effect of lung liquid replacement on any of the known flows into and out of the amniotic fluid. Although intramembranous absorption increased greatly during supplementation, the amniochorionic function curves were not altered by isovolemic lung liquid replacement. We conclude that lung liquid does not appear to contain a significant regulatory substance for amniotic fluid volume control.

Antenatal testing-a reevaluation: executive summary of a Eunice Kennedy Shriver National Institute of Child Health and Human Development workshop

In August 2007, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institutes of Health Office of Rare Diseases, the American College of Obstetricians and Gynecologists, and the American Academy of Pediatrics cosponsored a 2-day workshop to reassess the body of evidence supporting antepartum assessment of fetal well-being, identify key gaps in the evidence, and formulate recommendations for further research. Participants included experts in obstetrics and fetal physiology and representatives from relevant stakeholder groups and organizations. This article is a summary of the discussions at the workshop, including synopses of oral presentations on the epidemiology of stillbirth and fetal neurological injury, fetal physiology, techniques for antenatal monitoring, and maternal and fetal indications for monitoring. Finally, a synthesis of recommendations for further research compiled from three breakout workgroups is presented.

Oligohydramnios and associated fetal complications

During intrauterine life the fetus is bathed in amniotic fluid which provides a low resistance space for free movement and a buffer against external trauma. This fluid is produced in early pregnancy largely as a maternal dialysate, then as a fetal transudate. Fetal urine is the most important source of amniotic fluid after 16 weeks gestation. The control of amniotic fluid is complex and poorly understood; it arises from secondary partitioning of water within the fetoplacental extracellular space and reflects fetal fluid balance.

Amniotic fluid volume dynamics

From the moment of implantation until delivery some 37 weeks later, the human embryo or fetus is surrounded by fluid. Initially this fluid is a transudate from maternal and embryonic tissues which provides nutrients for the growing embryo. Starting in early pregnancy, the fetal kidneys begin to contribute substantial quantities of urine to the amniotic fluid volume. At mid pregnancy, when the skin becomes keratinized, the kidneys become the main source of amniotic fluid. Fetal swallowing is the main route of amniotic fluid removal. Although fetal urine production and swallowing have been studied in both human pregnancy and animal models, the knowledge from these investigations is not sufficiently extensive to explain overall amniotic fluid volume regulation. None the less, it is clear that the amniotic fluid is in a dynamic, ever-changing state. The production rate of the fetal urine in the human fetus at term (800–1200ml/day) is sufficient to replace completely the entire amniotic volume every 12–24 hours1. While the fetus is producing large volumes of urine, the volume of amniotic fluid is normally maintained within a very narrow range. Deviations from the normal range are often associated with significant perinatal morbidity and mortality.

Amniotic fluid abnormalities

The complex nature of amniotic fluid reflects contributions from many fetal systems, many functional roles, and multiple interactions with fetal maturation, obstetric, and maternal factors. Simple ultrasound measurement, probably done best with the maximum vertical pocket method, has a clinical role in fetal surveillance, substantiated by extensive level II and some level I evidence. Interventions (amnioinfusion for oligohydramnios, amnioreduction for polyhydramnios) have not been studied effectively in controlled fashion, with the exception of intrapartum applications, where effective reduction of cesarean delivery for fetal distress and perinatal impacts of meconium aspiration may follow amnioinfusion. A wealth of research opportunities exists into regulation of amniotic fluid constituents and their relation to preterm delivery.