The yolk sac in early pregnancy failure

Sonographic markers of aneuploidies at 6-10 weeks of gestation

OBJECTIVES

To determine if sonographic features of live embryos at 6-10 weeks' gestation are altered in aneuploidies.

METHODS

Embryonic crown rump length (CRL), embryonic heart rate, gestational sac diameter (GSD) and yolk sac diameter (YSD) were measured by transvaginal sonography in 5603 live embryos from singleton pregnancies at 6-10 weeks' gestation. The measurements were expressed as differences from the expected normal mean for CRL (delta values) and median delta values in the aneuploid cases were compared to the euploid group.

RESULTS

5393 pregnancies resulted in the live birth of phenotypically normal neonates and these cases constituted the euploid group. In 55 cases there was subsequent prenatal diagnosis of aneuploidies (trisomy 21, n=28; trisomy 18, n=10; trisomy 13, n=10; triploidy, n=4; Turner syndrome, n=3). The median and interquartile range (IQR) of delta embryonic heart rate in trisomy 18 was -19.44 (-23.77 to -7.20)bpm and in trisomy 13 it was 11.12 (7.25 to 20.39)bpm, which were significantly lower and higher, respectively, than in euploid embryos (median -0.05, IQR -6.18 to 6.21bpm). The median delta YSD in trisomy 21 was higher than in euploid fetuses (median 0.56, IQR 0.23 to 0.79 and median -0.17, IQR -3.11 to 2.82 mm). There were no other significant differences in measurements between the groups.

CONCLUSION

At 6-10 weeks' gestation there are sonographically detectable differences between euploid and trisomic embryos.

Ultrasonographic prediction of early miscarriage

BACKGROUND

The aim of this retrospective study was to assess the value of maternal history and ultrasound scan findings at 6-10 weeks for predicting early miscarriage.

METHODS

Embryonic crown-rump length (CRL), heart rate (HR), gestational sac diameter (GSD) and yolk sac diameter (YSD) were compared in two groups of women with singleton pregnancies attending an early pregnancy unit. In the first group the initial scan demonstrated a live embryo but in a subsequent visit the scan showed a dead embryo, complete or incomplete miscarriage. In the second group with a live embryo there was subsequent live birth of a normal neonate.

RESULTS

There were 729 pregnancies with miscarriage and 4698 with normal outcome. Logistic regression analysis demonstrated that in the prediction of miscarriage the risk was higher in women of African racial origin [odds ratio (OR) 1.62], cigarette smokers (OR 1.91) and those with vaginal bleeding (OR 2.03) and increased with maternal age (OR 1.05) and YSD (OR 1.88) and was inversely related to CRL (OR 0.79), HR (OR 0.96) and GSD (OR 0.84). At false-positive rate of 30%, the detection rate of miscarriage in screening by vaginal bleeding was 45%, 53% by the addition of maternal history factors and 85.7% by the addition of ultrasound findings.

CONCLUSIONS

In early pregnancy a prediction of miscarriage can be provided by a combination of maternal characteristics and ultrasound findings and the estimated risk can be used to rationalize follow-up. Our multivariate model requires prospective evaluation in a new sample population.

Is the yolk sac a new marker for chromosomal abnormalities in early pregnancy?

INTRODUCTION

Abnormal yolk sac size is associated with fetal miscarriage. This is a case report of two pregnancies with abnormal yolk sacs.

MATERIALS AND METHODS

In one case, a twofold sac was found; in the other case, the yolk sac was not of spherical form.

CONCLUSION

Currently available publications demonstrate a correlation between abnormal yolk sac size and miscarriage. However, in both cases a trisomy was confirmed. It should therefore be discussed whether form and size of the yolk sac could be a marker for chromosomal abnormalities of the fetus.

Ultrasonic morphological characteristics of yolk sac in pregnancy complicated with type-1 diabetes mellitus

BACKGROUND/AIMS

In pregnancy complicated with type-1 diabetes mellitus (DM), information on the predictive value of yolk sac (YS) measurement and YS morphology on outcome has been scant. The aim of this study was to compare the size and shape of the YS using transvaginal sonography (TVS) in normal pregnancies and those complicated with well-regulated type-1 DM.

METHODS

Sixty healthy pregnant women and 60 pregnant women with type-1 DM underwent TVS. The correlation coefficients between YS and gestational age (GA), YS and crown-rump length (CRL), and YS and human chorionic gonadotropin (HCG) were calculated. Statistical analysis showed that the difference between the YS diameters for each gestational week among the groups studied was highly statistically significant. Statistical analysis of the results was performed with SPSS 10 software.

RESULTS

A highly statistically positive correlation was found between YS diameter and GA, CRL and HCG levels for both groups studied. The YS diameter in type-1 DM pregnancies was statistically significantly larger for GA than that of healthy pregnant women. The YS diameter in type-1 DM women was statistically significantly larger after 6 weeks of gestation and the HbA1c levels were >6% when compared to the YS dimensions in the group with HbA1c concentrations of <6%.

CONCLUSION

A gross change in YS size may indicate or reflect significant dysfunction of the maternofetal transport system in early pregnancy which is complicated with type-1 DM.

Ultrasound evaluation of first trimester pregnancy complications

OBJECTIVE

To review the biological effects and safety of obstetric ultrasound.

OUTCOME

Outline the circumstances in which safety may be a concern with obstetric ultrasound.

EVIDENCE

Medline was searched, and a review of a document on this subject published by Health Canada and of bibliographies from identified articles was conducted.

VALUES

Review by principal authors and the Diagnostic Imaging Committee of the SOGC. The level of evidence was judged as outlined by the Canadian Task Force on the Periodic Health Examination.

BENEFITS, HARMS AND COSTS

Obstetric ultrasound should only be done for medical reasons, and exposure should be kept as low as reasonably achievable (ALARA) because of the potential for tissue heating. Higher energy is of particular concern for pulsed Doppler, colour flow, first trimester ultrasound with a long transvesical path (> 5 cm), second or third trimester exams when bone is in the focal zone, as well as when scanning tissue with minimal perfusion (embryonic) or in patients who are febrile. Operators can minimize risk by limiting dwell time, limiting exposure to critical structures, and following equipment generated exposure information. Recommendations 1. Obstetric ultrasound should only be used when the potential medical benefit outweighs any theoretical or potential risk (II-2A). 2. Obstetric ultrasound should not be used for nonmedical reasons, such as sex determination, producing nonmedical photos or videos, or for commercial purposes ( III-B). 3. Ultrasound exposure should be as low as reasonably achievable (ALARA) because of the potential for tissue heating when the thermal index exceeds 1. Exposure can be reduced through the use of output control and (or) by reducing the amount of time the beam is focused on one place (dwell time) (II-1A). 4. All diagnostic ultrasound devices should comply with the output display standards (MI and TI) (III-B). 5. When ultrasound is done for research or teaching purposes, exposed individuals should be informed if either the MI or TI are greater than 1 and how this exposure compares to that found in normal diagnostic practice (III-B). 6. While imaging the fetus in the first trimester, Doppler and colour Doppler should be avoided (III-B).

Sonographic evaluation of first-trimester bleeding

Vaginal bleeding is a leading cause of presentation for emergency care during the first trimester of the pregnancy. Clinical assessment of the pregnancy outcome at this stage is less reliable. US examination is crucial in establishing IUP and early pregnancy failure and to exclude other causes of bleeding, such as ectopic pregnancy and molar pregnancy. Diagnosis of a normal IUP at this stage not only assists the physician in an expectant management, but also gives a psychologic boost to the patient. With recent advances in US technology and the availability of high-frequency transvaginal transducers, reliable diagnosis of early pregnancy failure can be made even before the embryo is visible.

Ectopic pregnancy

Ectopic pregnancy is a high-risk diagnosis that is increasing in frequency and is still commonly missed in the emergency department. The emergency physician needs a high index of suspicion and must understand that the history, physical examination, and a single quantitative beta-hCG level cannot reliably rule out an ectopic pregnancy. Most pregnant patients who present to the emergency department during the first trimester with abdominal or pelvic pain, regardless of the presence of vaginal bleeding, should undergo further evaluation with ultrasonography. Ultrasound findings in conjunction with quantitative beta-hCG levels guide the management of the patient.

Yolk sacs in twin pregnancy

OBJECTIVE

The purpose of this study was to evaluate the relationship between the yolk sacs separated or not separated by septum and chorionicity twin pregnancies scanned early in the first trimester, and the relation between size and morphologic features of the yolk sac and the outcome of twin pregnancies.

RESULTS

In all 38 sets of twins two yolk sacs were identified. During the first trimester of a dichorionic twin pregnancy, the yolk sacs were always separated by a septum and not separated ("Eight" sign) in monochorionic twin pregnancy. In five cases, one of yolk sac was abnormally large (> 8 mm) and had thin wall. Four of the five mothers spontaneously aborted during the next 2-3 weeks. In one case of monochorionic twin ectopic pregnancy two yolk sacs were seen normally.

CONCLUSION

The sonographic identification of yolk sacs in multiple pregnancies allows an early and efficient recognition of presence and chorionicity of twin pregnancy, both in intra- and extrauterine. Identification of abnormal yolk sac or yolk sacs suggests death of one or all embryos.

Yolk sac size and shape as predictors of poor pregnancy outcome

Two hundred and fifty women, underwent endovaginal sonography in the first trimester to establish the normal size and shape of the secondary yolk sac and to assess the value of yolk sac evaluation in predicting poor pregnancy outcome. We calculated the correlation coefficients between yolk sac and menstrual age, yolk sac and crown-rump length and between yolk sac and mean gestational yolk sac diameter as r: 0.9581 (p < 0.001), r: 0.9427 (p < 0.0001) and r: 0.8855 (p < 0.0001), respectively. Of 250 cases, 219 had a normal pregnancy course through the end of the first trimester (Group I) while 31 had a poor prognosis such as abortion or embryonic demise (Group II). Eight of 219 in Group I and 20 of 31 in Group II had an abnormal yolk sac size. A yolk sac diameter out of two standard deviations of the mean for the menstrual age allowed prediction of an abnormal pregnancy outcome with a sensitivity of 65%, a specificity of 97%, a positive predictive value of 71%, and a negative predictive value of 95%. Ten of 219 and 9 of 31 had abnormal yolk sac shape. An abnormal yolk sac shape allowed prediction of an abnormal pregnancy outcome with a sensitivity of 29%, a specificity of 95%, a positive predictive value of 47% and a negative predictive value of 90.5%. We concluded that secondary yolk sac evaluation is a valuable tool to predict pregnancy outcome.

Role of pelvic ultrasonography in evaluation of symptomatic first-trimester pregnancy

Early identification of an abnormal pregnancy is important. The diagnosis of ectopic pregnancy before tubal rupture can prevent life-threatening hemorrhage. This article provides a review of the normal development in early pregnancy and correlates this with ultrasound findings, followed by a structured approach to the ultrasound examination. The specific findings in early pregnancy are reviewed, and the predictive value of these findings in identifying either a normal or abnormal intrauterine pregnancy or an ectopic pregnancy are discussed.

Transvaginal sonography of the yolk sac in normal and abnormal pregnancy

A cross-sectional study comprising 117 consecutive first trimester singleton pregnancies was performed using transvaginal sonography (TVS) to evaluate size abnormalities of the secondary yolk sac (YS) vis-à-vis pregnancy outcome. In normal pregnancy outcome (NPO) the YS diameter showed an increase from the 5th to the 11th week, menstrual age, followed by a decrease and its disappearance after 12 weeks. A YS of abnormal size was statistically significant (p < 0.001) in spontaneous abortion (SA) versus NPO, with a sensitivity of 68.7%, a specificity of 99%, a positive predictive value of 91.6% and a negative predictive value of 95.2%. These preliminary results indicate that a measurement of the YS very early in gestation may be a useful marker of pregnancy outcome.

Yolk sac concentration of prostaglandin E2 in diabetic pregnancy: further clues to the etiology of diabetic embryopathy

Fetal malformation associated with maternal diabetes occurs before the seventh week of pregnancy. Current hypotheses suggest that the diabetic milieu causes a reduction in phosphatidylinositol turnover, leading to a disruption in the arachidonic acid cascade and resulting in a deficiency of prostaglandins, particularly prostaglandin E2. This in turn results in a wide variety of congenital anomalies. This hypothesis has not been tested experimentally in humans. The yolk sac is thought to be the most important source of nutrition in early pregnancy. We sought to compare yolk sac prostaglandin levels in normal and diabetic women. Under ultrasonographic guidance, yolk sacs were aspirated form 8 normal and 12 diabetic women ranging from 8 to 10 weeks gestational age prior to elective abortion. Prostaglandin E2 levels were determined using RIA. The mean prostaglandin E2 level in normal controls was 3605 pg/mL, and was undetected in all of the yolk sacs aspirated from diabetic women (P < 0.001). Yolk sac diameter in diabetic pregnancies was 1.2 mm larger than that of normal pregnancies. The functional and morphological changes demonstrated in this study may increase our understanding of the pathophysiology of diabetic embryopathy.

Early human nutrition

The Human yolk sac has long been considered a vestigial organ, an evolutionary remnant. In the last decade, however, it has been discovered that the human yolk sac plays an active and crucial role during organogenesis. Due to an absent maternal intervillous circulation during the first 12 weeks of pregnancy, the concept of transport of nutrients and oxygen to the embryo must be thoroughly reconsidered. Here the yolk sac plays an essential role by its active and passive transport to the embryo, and by its production of necessary substances. Animal experiments have demonstrated that hyperglycaemia has an initial deleterious effect on yolk sac structure, which then results in embryopathy. Study of the yolk sac by means of ultrasound has not become an important diagnostic method yet. On the basis of clinical studies and animal experiments, however, it may be expected that this organ plays a crucial role in the development of spontaneous abortion and structural congenital defects.

Vascularization of yolk sac and vitelline duct in normal pregnancies studied by transvaginal color and pulsed Doppler

The yolk sac is an organ of increasingly recognized importance in the initial mechanisms of pregnancy maintenance and the early growth and welfare of the embryo. Having a complex protein secretion and an equally intricate ultrastructure, it is the primary source of blood and germ cells. This small and to date largely ignored structure may have a vital and interesting part to play in human embryonic development, which may be comparable to its proven evolutionary importance in other animals. The aim of our study was to assess the vascularity of the yolk sac and vitelline duct in 105 patients between the 6th and 10th weeks of gestation who were scheduled for termination of pregnancy for psychosocial reasons. The patients were divided in five subgroups depending on the duration of gestation. All of them had a normal developing pregnancy with no clinical symptoms of pathology (e.g. bleeding in early pregnancy). Gestational age was calculated from the first day of the last menstrual period and substantiated by crown-rump (CRL) measurements. After exploration of the gestational sac and embryo by transvaginal sonography, color Doppler was used to image the yolk sac and vitelline duct vascularity. The visualized vessels were analyzed with pulsed Doppler using the sample volume unit set of 1 mm. The assessment of obtained waveform signals was made by means of peak systolic Doppler shift (PSV) and pulsatility index (PI). The pulsatility index was calculated as a difference between peak systolic and end diastolic Doppler shift divided by the mean maximum velocity. At least 5 separate cardiac cycles were measured, and the mean value was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental manipulation of the rodent visceral yolk sac

The visceral yolk sac (VYS) is an especially important placental organ in the rodent because it is the primary source of exchange between the embryo and mother during early organogenesis before the chorioallantoic placenta circulation is established. The VYS is involved with nutritional, endocrine, metabolic, immunologic, secretory, excretory, and hematopoietic functions. The VYS also plays a role in steroid metabolism and interacts with a variety of blood-borne factors: parathyroid hormone, glucocorticoids, insulin, and vitamin D metabolites. The importance of the VYS during development is emphasized by the embryotoxicity resulting from exposure to agents which cause VYS dysfunction when administered to the pregnant animal during organogenesis. Several experimental procedures have provided useful information concerning a variety of VYS functions from early organogenesis to term: Culture of the Embryo, Fetal Incubation, Culture of the Fetus, Giant Yolk Sac, Short- and Long-Term Culture of the Yolk Sac, Modified Ussing's Chamber, Single or Double Diffusion Chamber, and the use of Heterologous Rodent Visceral Yolk Sac Antibodies. Since human yolk sac pathology has been associated with developmental toxicity and spontaneous abortion, it is important to discover whether there are some common functional roles among different mammalian species and to determine if other experimental animal models can be used to study the possible contribution of human yolk sac dysfunction to some human reproductive problems.