The sonographically thick placenta: a predictor of increased perinatal morbidity and mortality

Correlation Between Ultrasonographic Placental Thickness and Adverse Fetal and Neonatal Outcomes

Introduction The placenta is often overlooked in the routine evaluation of normal gestations, receiving attention only when abnormalities are detected. Placental thickness can serve as a good predictor of fetal growth and birth weight, especially in the second trimester.In this prospective study, we measured placental thickness in the second and third trimesters of singleton pregnancies and identified an association between placental thickness and adverse outcomes such as congenital anomalies, fetal growth restriction (FGR), prematurity, low birth weight, stillbirth, and hydrops fetalis. Methodology A total of 298 patients aged 20 to 33 years with a singleton pregnancy and regular cycles, who were sure of the date of their last menstrual period, were observed. Placental thickness was measured by ultrasound at 18-20 and 30-32 weeks, and patients were divided into three groups. Group A consisted of patients with normal placental thickness. Group B included patients with a thin placenta (below the 10th percentile). Group C consisted of patients with a thick placenta (above the 95th percentile). The correlation between placental thickness and the fetal and neonatal outcome was observed. Results Out of 298 patients, 82 (27.5%) were primigravida and 216 (72.4%) were multigravida. At 18-20 weeks, premature birth was observed in one patient (7.69%) in Group C and six patients (20%) in Group B, compared with eight patients (3.14%) in Group A. At 30-32 weeks, premature birth was seen in two patients (16.67%) in Group C and 11 patients (36.67%) in Group B, compared with two patients (0.78%) in Group A. At 18-20 weeks of gestation, low birth weight was observed for three patients (23.08%) in Group C and 16 patients (53.33%) in Group B, compared with 15 patients (5.88%) in Group A. At 30-32 weeks, low birth weight was observed for four patients (33.33%) in Group C and 19 patients (63.33%) in Group B compared with 11 patients (4.30%) in Group A. A significant association was found between a thin placenta and low birth weight and prematurity at both 18-20 and 30-32 weeks of gestation. Two patients (13.33%) had major congenital abnormalities and a thick placenta at 18-20 weeks. In Group C, hydrops were observed in two patients (15.38%) at 18-20 weeks and two patients (16.67%) at 30-32 weeks. A significant association was found between a thick placenta and hydrops. At 30-32 weeks, 13 patients (43.33%) in Group B had developed FGR compared with six patients (2.34%) with a normal placenta. A significant association was found between a thin placenta and FGR. One patient (7.69%) with a thick placenta had a stillbirth, indicating a nonsignificant association. Conclusions A positive correlation was observed between congenital anomalies and hydrops and a thick placenta, whereas FGR, preterm labor, prematurity, and low birth weight were associated with a thin placenta. Subnormal placental thickness for a particular gestational age may be the earliest sign of FGR. A sonographically identified abnormal placenta should alert clinicians to the possibility of a compromised perinatal outcome and the need for evaluation and close follow-up.

Contribution of Second Trimester Sonographic Placental Morphology to Uterine Artery Doppler in the Prediction of Placenta-Mediated Pregnancy Complications

Background: Second-trimester uterine artery Doppler is a well-established tool for the prediction of preeclampsia and fetal growth restriction. At delivery, placentas from affected pregnancies may have gross pathologic findings. Some of these features are detectable by ultrasound, but the relative importance of placental morphologic assessment and uterine artery Doppler in mid-pregnancy is presently unclear. Objective: To characterize the association of second-trimester sonographic placental morphology markers with placenta-mediated complications and determine whether these markers are predictive of placental dysfunction independent of uterine artery Doppler. Methods: This was a retrospective cohort study of patients with a singleton pregnancy at high risk of placental complications who underwent a sonographic placental study at mid-gestation (160/7−246/7 weeks’ gestation) in a single tertiary referral center between 2016−2019. The sonographic placental study included assessment of placental dimensions (length, width, and thickness), placental texture appearance, umbilical cord anatomy, and uterine artery Doppler (mean pulsatility index and early diastolic notching). Placental area and volume were calculated based on placental length, width, and thickness. Continuous placental markers were converted to multiples on medians (MoM). The primary outcome was a composite of early-onset preeclampsia and birthweight < 3rd centile. Results: A total of 429 eligible patients were identified during the study period, of whom 45 (10.5%) experienced the primary outcome. The rate of the primary outcome increased progressively with decreasing placental length, width, and area, and increased progressively with increasing mean uterine artery pulsatility index (PI). By contrast, placental thickness followed a U-shaped relationship with the primary outcome. Placental length, width, and area, mean uterine artery PI and bilateral uterine artery notching were all associated with the primary outcome. However, in the adjusted analysis, the association persisted only for placenta area (adjusted odds ratio [aOR] 0.21, 95%-confidence interval [CI] 0.06−0.73) and mean uterine artery PI (aOR 11.71, 95%-CI 3.84−35.72). The area under the ROC curve was highest for mean uterine artery PI (0.80, 95%-CI 0.71−0.89) and was significantly higher than that of placental area (0.67, 95%-CI 0.57−0.76, p = 0.44). A model that included both mean uterine artery PI and placental area did not significantly increase the area under the curve (0.82, 95%-CI 0.74−0.90, p = 0.255), and was associated with a relatively minor increase in specificity for the primary outcome compared with mean uterine artery PI alone (63% [95%-CI 58−68%] vs. 52% [95%-CI 47−57%]). Conclusion: Placental area is independently associated with the risk of placenta-mediated complications yet, when combined with uterine artery Doppler, did not further improve the prediction of such complications compared with uterine artery Doppler alone.

Thick Placenta in Pregnancy: A Review

Importance

A thickened placenta is easily identified on ultrasound and provides insight into maternal and fetal wellbeing as well as underlying structural and physiologic anomalies.

Objectives

The aim of this study was to review the literature to clarify what classifies a placenta as "thickened" and to review the associated incidence, maternal and fetal comorbidities, and management during pregnancy.

Evidence Acquisition

Electronic databases (PubMed and Web of Science) were searched from 2000 to 2020 in the English language. Studies were selected that examined associations between placental thickness, potential etiologies, and obstetric outcomes.

Results

There were 140 abstracts identified. After reviewing the articles, 60 were used in this review. Routine assessment of the placenta in the prenatal period is an easy and inexpensive way to assess the maternal and fetal patients. The criteria for a "thickened placenta" vary between studies based on gestational age, placental location, measurement technique, and maternal or fetal factors. Whereas most suggest thickness exceeding 4 cm is pathologic, a review had a threshold of 6 cm in the third trimester to classify placentomegaly. Several maternal and fetal conditions have been associated with a thickened placenta, such as obesity, parity, anemia, diabetes, preeclampsia, cardiac dysfunction, infection, assisted reproductive technology, multiple pregnancy, sacrococcygeal teratomas, and Beckwith-Wiedemann syndrome. A thickened placenta in pregnancy is associated with a higher incidence of adverse pregnancy outcomes and neonatal morbidity and mortality.

Conclusions

The literature is clear that early evaluation of the placenta using ultrasound should be a standard practice. A thickened placenta found on routine imaging should prompt a more thorough investigation to determine the etiology of the placentomegaly. At the time of this literature review, there are no recommendations regarding modality or frequency of antenatal surveillance in pregnancies complicated by a thickened placenta. However, serial ultrasounds and weekly antenatal testing in the third trimester should be considered.

Relevance

A thickened placenta has been associated with a variety of maternal and fetal conditions and increases the risk of adverse pregnancy outcomes and neonatal morbidity and mortality.

Insights into the role of placenta thickness as a predictive marker of perinatal outcome

The placenta is a transitory organ indispensable for normal fetal maturation and growth. Recognition of abnormal placental variants is important in clinical practice, and a broader understanding of the significance of placental variants would help clinicians better manage affected pregnancies. Increased thickness of the placenta is reported to be a nonspecific finding but it is associated with many maternal and fetal abnormalities, including preeclampsia and abnormal fetal growth. In this review, we address the questions regarding the characteristics of placenta thickness and the relationship between thickened placenta and poor pregnancy outcomes.

Placental infection by Zika virus in French Guiana

OBJECTIVES

To describe placental findings on prenatal ultrasound and anatomopathological examination in women with Zika virus (ZIKV) infection, and to assess their association with congenital ZIKV infection and severe adverse outcome, defined as fetal loss or congenital Zika syndrome (CZS).

METHODS

This was a prospective study of pregnancies undergoing testing for maternal ZIKV infection at a center in French Guiana during the ZIKV epidemic. In ZIKV-positive women, congenital infection was defined as either a positive reverse transcription polymerase chain reaction result or identification of ZIKV-specific immunoglobulin-M in at least one placental, fetal or neonatal sample. Placental ZIKV-infection status was classified as non-exposed (placentae from non-infected women), exposed (placentae from ZIKV-infected women without congenital infection) or infected (placentae from ZIKV-infected women with proven congenital infection). Placentae were assessed by monthly prenatal ultrasound examinations, measuring placental thickness and umbilical artery Doppler parameters, and by anatomopathological examination after live birth or intrauterine death in women with ZIKV infection. The association of placental thickness during pregnancy and anatomopathological findings with the ZIKV status of the placenta was assessed. The association between placental findings and severe adverse outcome (CZS or fetal loss) in the infected group was also assessed.

RESULTS

Among 291 fetuses/neonates/placentae from women with proven ZIKV infection, congenital infection was confirmed in 76 cases, of which 16 resulted in CZS and 11 resulted in fetal loss. The 215 remaining placentae from ZIKV-positive women without evidence of congenital ZIKV infection represented the exposed group. A total of 334 placentae from ZIKV-negative pregnant women represented the non-exposed control group. Placentomegaly (placental thickness > 40 mm) was observed more frequently in infected placentae (39.5%) than in exposed placentae (17.2%) or controls (7.2%), even when adjusting for gestational age at diagnosis and comorbidities (adjusted hazard ratio (aHR), 2.02 (95% CI, 1.22-3.36) and aHR, 3.23 (95% CI, 1.86-5.61), respectively), and appeared earlier in infected placentae. In the infected group, placentomegaly was observed more frequently in cases of CZS (62.5%) or fetal loss (45.5%) than in those with asymptomatic congenital infection (30.6%) (aHR, 5.43 (95% CI, 2.17-13.56) and aHR, 4.95 (95% CI, 1.65-14.83), respectively). Abnormal umbilical artery Doppler was observed more frequently in cases of congenital infection resulting in fetal loss than in those with asymptomatic congenital infection (30.0% vs 6.1%; adjusted relative risk (aRR), 4.83 (95% CI, 1.09-20.64)). Infected placentae also exhibited a higher risk for any pathological anomaly than did exposed placentae (62.8% vs 21.6%; aRR, 2.60 (95% CI, 1.40-4.83)).

CONCLUSIONS

Early placentomegaly may represent the first sign of congenital infection in ZIKV-infected women, and should prompt enhanced follow-up of these pregnancies. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

The predictive value of sonographic placental markers for adverse pregnancy outcome in women with chronic kidney disease

OBJECTIVE

To determine the rate of sonographic placental markers and their predictive value for preeclampsia and fetal growth restriction in women with chronic kidney disease (CKD).

STUDY DESIGN

A retrospective cohort study of women with CKD followed at a tertiary referral center between 2016 and 2019 (n = 86). All women underwent 2nd trimester sonographic placental examinations that included assessment of placental morphology, umbilical cord, and uterine artery Doppler. Continuous placental markers were converted to multiples on medians (MoM).

MAIN OUTCOME MEASURES

Predictive value of sonographic markers for preeclampsia and birthweight < 10th percentile.

RESULTS

Women in the cohort had a high rate of preeclampsia (24.4%), birthweight < 10th% (26.7%), and preterm birth (30.2%). The most important markers were placental volume and uterine artery Doppler: the risk of preeclampsia was elevated in women with low placental volume (51.7% vs. 10.9%; OR = 8.79 [2.70-28.59] for preeclampsia; and 40.0% vs. 9.1%; OR = 6.67 [1.85-24.04] for preterm preeclampsia), and in women with bilateral uterine artery notching (62.5% vs. 20.8%; OR = 6.35 [1.37-29.45] for preeclampsia; and 62.5% vs. 10.4%; OR = 14.38 [1.29-71.75] for preterm preeclampsia). The combination of both markers had the strongest predictive value for preeclampsia (positive likelihood ratio = 8.25 [6.84-9.95]). Low placental volume and bilateral uterine notching were also associated with birthweight < 10th percentile.

CONCLUSION

A 2nd-trimester sonographic placental study can identify a subgroup of women with CKD who are at most risk of preeclampsia and fetal growth restriction. Such data may inform their subsequent perinatal care and assist care providers in the often challenging distinction between preeclampsia flare of underlying CKD.

Biochemical tests of placental function versus ultrasound assessment of fetal size for stillbirth and small-for-gestational-age infants

BACKGROUND

Stillbirth affects 2.6 million pregnancies worldwide each year. Whilst the majority of cases occur in low- and middle-income countries, stillbirth remains an important clinical issue for high-income countries (HICs) - with both the UK and the USA reporting rates above the mean for HICs. In HICs, the most frequently reported association with stillbirth is placental dysfunction. Placental dysfunction may be evident clinically as fetal growth restriction (FGR) and small-for-dates infants. It can be caused by placental abruption or hypertensive disorders of pregnancy and many other disorders and factorsPlacental abnormalities are noted in 11% to 65% of stillbirths. Identification of FGA is difficult in utero. Small-for-gestational age (SGA), as assessed after birth, is the most commonly used surrogate measure for this outcome. The degree of SGA is associated with the likelihood of FGR; 30% of infants with a birthweight < 10th centile are thought to be FGR, while 70% of infants with a birthweight < 3rd centile are thought to be FGR. Critically, SGA is the most significant antenatal risk factor for a stillborn infant. Correct identification of SGA infants is associated with a reduction in the perinatal mortality rate. However, currently used tests, such as measurement of symphysis-fundal height, have a low reported sensitivity and specificity for the identification of SGA infants.

OBJECTIVES

The primary objective was to assess and compare the diagnostic accuracy of ultrasound assessment of fetal growth by estimated fetal weight (EFW) and placental biomarkers alone and in any combination used after 24 weeks of pregnancy in the identification of placental dysfunction as evidenced by either stillbirth, or birth of a SGA infant. Secondary objectives were to investigate the effect of clinical and methodological factors on test performance.

SEARCH METHODS

We developed full search strategies with no language or date restrictions. The following sources were searched: MEDLINE, MEDLINE In Process and Embase via Ovid, Cochrane (Wiley) CENTRAL, Science Citation Index (Web of Science), CINAHL (EBSCO) with search strategies adapted for each database as required; ISRCTN Registry, UK Clinical Trials Gateway, WHO International Clinical Trials Portal and ClinicalTrials.gov for ongoing studies; specialist abstract and conference proceeding resources (British Library's ZETOC and Web of Science Conference Proceedings Citation Index). Search last conducted in Ocober 2016.

SELECTION CRITERIA

We included studies of pregnant women of any age with a gestation of at least 24 weeks if relevant outcomes of pregnancy (live birth/stillbirth; SGA infant) were assessed. Studies were included irrespective of whether pregnant women were deemed to be low or high risk for complications or were of mixed populations (low and high risk). Pregnancies complicated by fetal abnormalities and multi-fetal pregnancies were excluded as they have a higher risk of stillbirth from non-placental causes. With regard to biochemical tests, we included assays performed using any technique and at any threshold used to determine test positivity.

DATA COLLECTION AND ANALYSIS

We extracted the numbers of true positive, false positive, false negative, and true negative test results from each study. We assessed risk of bias and applicability using the QUADAS-2 tool. Meta-analyses were performed using the hierarchical summary ROC model to estimate and compare test accuracy.

MAIN RESULTS

We included 91 studies that evaluated seven tests - blood tests for human placental lactogen (hPL), oestriol, placental growth factor (PlGF) and uric acid, ultrasound EFW and placental grading and urinary oestriol - in a total of 175,426 pregnant women, in which 15,471 pregnancies ended in the birth of a small baby and 740 pregnancies which ended in stillbirth. The quality of included studies was variable with most domains at low risk of bias although 59% of studies were deemed to be of unclear risk of bias for the reference standard domain. Fifty-three per cent of studies were of high concern for applicability due to inclusion of only high- or low-risk women.Using all available data for SGA (86 studies; 159,490 pregnancies involving 15,471 SGA infants), there was evidence of a difference in accuracy (P < 0.0001) between the seven tests for detecting pregnancies that are SGA at birth. Ultrasound EFW was the most accurate test for detecting SGA at birth with a diagnostic odds ratio (DOR) of 21.3 (95% CI 13.1 to 34.6); hPL was the most accurate biochemical test with a DOR of 4.78 (95% CI 3.21 to 7.13). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.88 and median prevalence of 19%, EFW, hPL, oestriol, urinary oestriol, uric acid, PlGF and placental grading will miss 50 (95% CI 32 to 68), 116 (97 to 133), 124 (108 to 137), 127 (95 to 152), 139 (118 to 154), 144 (118 to 161), and 144 (122 to 161) SGA infants, respectively. For the detection of pregnancies ending in stillbirth (21 studies; 100,687 pregnancies involving 740 stillbirths), in an indirect comparison of the four biochemical tests, PlGF was the most accurate test with a DOR of 49.2 (95% CI 12.7 to 191). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.78 and median prevalence of 1.7%, PlGF, hPL, urinary oestriol and uric acid will miss 2 (95% CI 0 to 4), 4 (2 to 8), 6 (6 to 7) and 8 (3 to 13) stillbirths, respectively. No studies assessed the accuracy of ultrasound EFW for detection of pregnancy ending in stillbirth.

AUTHORS' CONCLUSIONS

Biochemical markers of placental dysfunction used alone have insufficient accuracy to identify pregnancies ending in SGA or stillbirth. Studies combining U and placental biomarkers are needed to determine whether this approach improves diagnostic accuracy over the use of ultrasound estimation of fetal size or biochemical markers of placental dysfunction used alone. Many of the studies included in this review were carried out between 1974 and 2016. Studies of placental substances were mostly carried out before 1991 and after 2013; earlier studies may not reflect developments in test technology.

A thick placenta: a predictor of adverse pregnancy outcomes

Purpose

The aim of this study is to evaluate the efficacy of an ultrasonographic measurement of placental thickness and the correlation of a thick placenta with adverse perinatal outcome.

Methods

Placental thickness was measured in single gravidas, 16 to 40 weeks of gestation, between 2005 and 2009. Placentas were considered to be thick if their measured thickness were above the 95th percentile for gestational age.

Results

The incidence of thick placentas was 4.3% (138/3,183). Perinatal morbidity and neonatal conditions were worse in cases with thick placenta rather than without thick placenta.

Conclusions

Ultrasonographic measurement of placental thickness is a simple method to estimate placental size. Thick placenta may be a useful predictor of adverse pregnancy outcomes.

Novel placental ultrasound assessment: potential role in pre-gestational diabetic pregnancy

OBJECTIVES

Management of women with pre-gestational diabetes continues to be challenging for clinicians. This study aims to determine if 3D power Doppler (3DPD) analysis of placental volume and flow, and calculation of placental calcification using a novel software method, differ between pregnancies with type 1 or type 2 diabetes and normal controls, and if there is a relationship between these ultrasound placental parameters and clinical measures in diabetics.

METHODS

This was a prospective cohort study of 50 women with diabetes and 250 controls (12-40 weeks gestation). 3DPD ultrasound was used to evaluate placental volume, vascularisation index (VI), flow index (FI) and vascularisation-flow index (VFI). Placental calcification was calculated by computer analysis. Results in diabetics were compared with control values, and correlated with early pregnancy HbA1c, Doppler results and placental histology.

RESULTS

Placental calcification and volume increased with advancing gestation in pre-gestational diabetic placentae. Volume was also found to be significantly higher than in normal placentae. VI and VFI were significantly lower in diabetic pregnancies between 35 and 40 weeks gestation. A strong relationship was seen between a larger placental volume and both increasing umbilical artery pulsatility index and decreasing middle cerebral artery pulsatility index. FI was significantly lower in cases which had a booking HbA1c level ≥6.5%. Ultrasound assessed placental calcification was reduced with a histology finding of delayed villous maturation. No other correlation with placental histology was found.

CONCLUSIONS

This study shows a potential role for 3D placental evaluation, and computer analysis of calcification, in monitoring pre-gestational diabetic pregnancies.

Placental thickness in the second trimester: a pilot study to determine the normal range

OBJECTIVES

We sought to determine the normal sonographically measured placental thickness in millimeters at the second-trimester scan (18 weeks to 22 weeks 6 days) and determine whether the measurement should be adjusted for gestational age and the placental site.

METHODS

We conducted a cross-sectional observational pilot study involving 114 consecutive patients with singleton pregnancies presenting for routine second-trimester sonography between 18 weeks and 22 weeks 6 days.

RESULTS

The unadjusted overall mean placental thickness was 24.6 (SD, 7.29) mm. The placental thickness was normally distributed. On multivariable analysis, the predicted mean thickness was 6.6 mm (95% confidence interval, 4.4 to 8.8 mm; P < .001) less in anterior compared to posterior or fundal placentas and increased by 0.6 mm (95% confidence interval, -0.5 to 1.7 mm; P = .27) for each week increase in gestation after 18 weeks

CONCLUSIONS

The placental position and possibly gestational age need to be considered when determining placental thickness. Anterior placentas are approximately 7 mm thinner than posterior or fundal placentas. Anterior placentas of greater than 33 mm and posterior placentas of greater than 40 mm should be considered abnormally thick.

Antithrombotic therapy for improving maternal or infant health outcomes in women considered at risk of placental dysfunction

BACKGROUND

Pregnancy complications such as pre-eclampsia and eclampsia, intrauterine growth restriction and placental abruption are thought to have a common origin related to abnormalities in the development and function of the placenta.

OBJECTIVES

To compare, using the best available evidence, the benefits and harms of antenatal antithrombotic therapy to improve maternal or infant health outcomes in women considered at risk of placental dysfunction, when compared with other treatments, placebo or no treatment.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (March 2010).

SELECTION CRITERIA

Randomised controlled trials comparing antenatal antithrombotic therapy (either alone or in combination with other agents) with placebo or no treatment, or any other treatment in the antenatal period to improve maternal or infant health outcomes in women considered at risk of placental dysfunction.

DATA COLLECTION AND ANALYSIS

Two review authors evaluated trials under consideration for appropriateness for inclusion and methodological quality without consideration of their results according to the prestated eligibility criteria. We used a fixed-effect meta-analysis for combining study data if the trials were judged to be sufficiently similar. We investigated heterogeneity by calculating I(2) statistic, and if this indicated a high level of heterogeneity among the trials included we used a random-effects model.

MAIN RESULTS

Our search strategy identified 14 reports of 10 studies for consideration, of which five met the inclusion criteria, involving 484 women. Four studies compared heparin (alone or in combination with dipyridamole) with no treatment; and one compared trapidil (triazolopyrimidine). While there were no statistically significant differences identified for the primary outcomes following heparin treatment, it was associated with a reduction in the risk of pre-eclampsia, eclampsia, and infant birthweight less than the 10th centile for gestational age.

AUTHORS' CONCLUSIONS

The review identified no significant differences for the primary outcomes perinatal mortality, preterm birth less than 34 weeks' gestation, and childhood neurodevelopmental handicap, although the number of studies and participants was small. While treatment with heparin appears promising with a reduction in pre-eclampsia, eclampsia, and infant birthweight less than the 10th centile for gestational age, the number of studies and participants included was small, and to date important information about serious adverse infant and long-term childhood outcomes is unavailable. Further research is required.

In utero imaging of the placenta: importance for diseases of pregnancy

Maurice Panigel demonstrated by X-rays, almost 40 years ago, placental maternal blood jets in non-human primates. Although to researchers the importance of the placenta is evident, in clinical obstetrical imaging, the fetus takes precedence. The placenta is imaged almost as an after thought and mostly to determine its location in the uterus. In animal species, the placenta was imaged with techniques which would be considered too invasive (or too costly for routine use) in humans, many pioneered by Panigel: radioangiography, radioisotopes scintigraphy, thermography, magnetic resonance imaging (MRI) and spectroscopy, positive emission tomography (PET) and single photon emission computed tomography (SPECT). Ultrasound allows for detailed, and, as far as is known, safe analyses of not only placental structure in the human but also its function. Earlier, only 2-dimensional grey-scale was available and more than 20 years ago, placental grading was popular. Later, colour imaging and spectral Doppler analysis of blood velocity both in the umbilical artery and within the placenta as well as the uterus and fetal vessels became essential and, more recently, the use of ultrasound contrast agents has been described, albeit not yet in a clinical setting. Three-dimensional ultrasound permits evaluation of the placenta in several planes, more precise depiction of internal vasculature as well as more accurate volume assessment. Several medical disorders of the pregnant woman or her fetus begin or end in the placenta, and ultrasound is the optimal investigation method. Obvious examples include pre-eclampsia and other forms of hypertension in pregnancy, less than optimal fetal growth (i.e. intrauterine growth restriction), triploidy (and its placental manifestation: partial mole), non-immune hydrops as well as several infectious processes. Ultrasound is also particularly suited to evaluate specific placental conditions, such as abnormal placentation (placenta previa and accrete for instance), gestational trophoblastic disease and placental tumors (e.g. chorioangioma).

Ultrasound detection of placental insufficiency in women with 'unexplained' abnormal maternal serum screening results

Serious placental insufficiency results in perinatal death or preterm birth from ischemic-thrombotic pathology, a process which has its origins in placental maldevelopment in the first trimester. A proportion of at-risk pregnancies may be identified from abnormalities in first or second trimester serum screening data, uterine artery Doppler waveforms or placental shape and texture at the time of the 18-20-week anatomical examination. In combination, these tests may be capable of recognizing a subset of at-risk pregnancies with 50% positive predictive values. Early recognition before fetal viability affords opportunities to direct women to regional perinatal care centres for enhanced maternal-fetal surveillance, corticosteroids to enhance fetal lung maturation, prophylactic measures to prevent pre-eclampsia and optimal decision making around the time of delivery. The creation of regional screening programs to use screening data with a placental focus is likely to be cost-effective, because existing patterns of care are utilized. More importantly, this strategy can direct women to participate in clinical research programs designed to reduce morbidity and mortality from this common group of conditions.

Are placental lakes of any clinical significance?

The aim of this study was to determine prospectively whether an association exists between the finding of placental lakes at the 20 week scan and an increased risk of uteroplacental complications or a poor pregnancy outcome. We studied the placental appearances in 1,198 consecutive second trimester ultrasound scans performed for routine foetal abnormality screening at our institution. The placental thickness was measured at its widest diameter in the sagittal plane and the presence or absence of placental lakes was recorded. The birth weight in each case was plotted against the centile charts in use at the hospital and recorded. Specific outcome measures included foetal growth restriction (IUGR) with a birth weight below the 5th centile, pre-eclampsia, placental abruption, and perinatal deaths. Placental lakes were seen in 17.8 per cent of the scans. There was no significant association with either maternal socio-demographic factors or perinatal mortality (OR 0.94, 95 per cent CI 0.35-2.51). No association was seen with maternal cigarette smoking (OR 1.07, 95 per cent CI 0.75-1.52), a birth weight below the 5th centile (OR 0.68, 95 per cent CI 0.39-1.18), the development of pregnancy induced hypertension (OR 0.68, 95 per cent CI 0.35-1.32), severe pre-eclampsia (OR 0.72, 95 per cent CI 0.21-2.50), or placental abruption (OR 1.79, 95 per cent CI 0.46-6.99). A finding of placental lakes was six times more likely with a thick placenta >3 cm at 20 weeks gestation (OR 6.30, 95 per cent CI 4.39 to 9.05). A finding of placental lakes during the second trimester ultrasound scan does not appear to be associated with uteroplacental complications or an adverse pregnancy outcome. The lesions are more prevalent with increasing placental thickness.

Sonographically thick placenta: a marker for increased perinatal risk--a prospective cross-sectional study

The aim of this study was to determine placental thickness by ultrasound examination throughout pregnancy and establish the correlation of sonographically thick placenta with perinatal mortality and morbidity. Placental thickness was determined by routine sonographic examination throughout pregnancy in 561 normal singleton pregnancies. Thick placenta was determined as placenta that was above the 90th percentile. Gravidae between 20-22 weeks' gestation (n=193) and 32-34 weeks (n=73) were then divided into two groups according to placental thickness. The study group consisted of 44 gravidae with thick placenta. The control group included 151 gravidae with placental thickness between the 10th and 90th percentile. A comparison of perinatal mortality and morbidity rates as well as the incidence of small and large for gestational age neonates was conducted.A linear increase of placental thickness was found to correlate with gestational age throughout pregnancy. No statistical differences were observed between the two groups with regard to obstetrical variables such as maternal age, parity and gestational age at delivery. No correlation was found between placental thickness and maternal age or parity. The incidence of perinatal mortality was significantly higher among gravidae with thick placentae (6.82% versus 0.66 per cent, P=0.037, 95 per cent confidence interval 1.71-70.29). Birthweight at term was found to be above 4000 g in 20.45 per cent of the thick-placenta group as compared to 5.3 per cent in the control group (P=0.001, 95 per cent CI 2.08-13.85), and birthweight of less than 2500 g was found in 15. 9 per cent of the thick-placenta group as compared to 7.3 per cent in the control group (P=0.03, 95 per cent CI 1.11-8.14). The incidence of fetal anomalies was 9.1 per cent in the thick-placenta group and 3.97 per cent in the control group (not significant). Sonographically thick placenta is associated with increased perinatal risk with increased mortality related to fetal anomalies and higher rates of both small for gestational age and large for gestational age infants at term.

Ultrasonographic investigation of placental morphologic characteristics and size during the second trimester of pregnancy

OBJECTIVE

The aim of the study was to establish the incidence of abnormal placental ultrasonographic findings in an unselected obstetric population and determine the usefulness of simple measurements of placental size. In addition, the relationship between these findings, uterine artery Doppler measurements, maternal serum alpha-fetoprotein levels, and subsequent pregnancy outcome was explored.

STUDY DESIGN

A prospective, cross-sectional study of 210 women recruited at the time of routine ultrasonographic scan between 16 and 28 weeks' gestation was performed. Placental ultrasonographic investigations included measurements of thickness, circumference, and volume and morphologic studies. Uterine Doppler and maternal serum alpha-fetoprotein measurements were performed at the same time.

RESULTS

At delivery 25 fetuses were small for gestational age, in association with hypertension in 11; 14 were delivered prematurely but were appropriately grown, and three were macrosomic. Significant correlations were found in uncomplicated pregnancies (n = 168) between gestational age and placental thickness, circumference, and volume and also between fetal abdominal and placental circumferences. Large sonolucent lakes were found with a similar incidence in both complicated and uncomplicated pregnancies. Jelly-like placental appearance was seen in 12 of the 17 cases complicated by hypertension, 11 of which also had abnormal uterine Doppler features and elevated maternal serum alpha-fetoprotein levels.

CONCLUSIONS

This study shows an association between abnormal placental development, ultrasonographic appearances, and subsequent abnormal fetal growth or hypertensive disorders of pregnancy. The interrelationships demonstrated between the different techniques suggest that a combination of placental thickness and morphologic characteristics, uterine Doppler analysis, and evaluation of maternal serum alpha-fetoprotein level may allow more efficient screening for these complications than is currently possible using any single method.