Correlation between Diameter of Yolk Sac on Transvaginal Ultrasonography at 6-12 Weeks of Gestation and Adverse Pregnancy Outcomes.

OBJECTIVE: To evaluate the correlation between yolk sac diameter at 6 to 12 weeks of gestation measured via transvaginal ultrasound and adverse pregnancy outcomes. METHODS: This prospective cohort study was conducted at the Ain Shams University Maternity Hospital from July 1, 2019 to January 30, 2020. It included 120 pregnant women attending the outpatient clinic at 6 to 12 weeks of gestation. Transvaginal ultrasound was performed to measure inner yolk sac diameter. Normal diameter was considered to be 2-5 mm. Cases were followed up in routine antenatal care until the 16th week of gestation. RESULTS: Significant associations were found between maternal age and yolk sac diameter; yolk sac diameter and early miscarriage; a high percentage of cases of positive fetal life occurred when a normal yolk sac diameter (2-5 mm) was present (p<0.001); in yolk sac diameters <2mm positive fetal life was 0.0% and negative fetal life was 42.9%; in yolk sac diameters of 2-5mm positive fetal life was 81.1% and the negative fetal life was 7.1%; and in yolk sac diameters >5mm positive fetal life was 18.9% and negative fetal life was 50.0% (p<0.001), x2 60.094; and the best cutoff value for yolk sac diameter was >0.56, with a sensitivity of 78.6%, a specificity of 84.3%. CONCLUSIONS: We found a highly significant correlation between yolk sac diameter and early pregnancy loss.

Ultrasonographic features of the regressing yolk sac of normal captive Brown kiwi chicks (Apteryx mantelli) vary with age.

Brown kiwi (Apteryx mantelli) are a culturally significant ratite species endemic to New Zealand. Chicks can develop diseases of the yolk sac which can be fatal if not promptly recognized and treated. Ultrasound examination of the yolk sac is an important component in the evaluation of chicks with suspected yolk sac disease. However, there are currently no reports of the normal ultrasonographic appearance of the regressing yolk sac in this species. The objective of this prospective reference interval study was to describe the normal ultrasonographic appearance of the yolk sac in brown kiwi chicks. Focused coelomic sonographic examinations were performed on 29 healthy chicks from >1 day of age until the yolk sac was completely absorbed or was <1 mL in volume. 41.6% (57/137) of yolks were round/ovoid in shape and 58.6% (80/137) had lobulated margins with invaginations. All yolks (137/137) were hyperechoic relative to adjacent coelomic structures. The heterogeneity of the echogenicity of the yolk was significantly associated with age (increased heterogeneity in younger birds) and was homogeneous, mildly heterogeneous, and moderately heterogeneous in 33% (46/138), 46% (63/138), and 21% (29/138) of all examinations respectively. Intrasac anechoic pockets were seen in 14% (20/139) of yolk sacs. The rate of yolk sac resorption slowed with age. In all examinations identifying a completely absorbed yolk sac or a yolk sac <1 mL in volume, chicks were less than 21 days old. The results of this study provide a reference of normal for the sonographic appearance of the yolk sac in captive brown kiwi chicks.

Morphological characteristics of zebrafish's yolk sac for malformation based on orthogonal-polarization-gating optical coherence tomography.

In this study, an automatic algorithm combining an ellipsoid approximation and U-net has been presented for the characterization of a zebrafish's yolk sac. The polarization-difference-balanced-detection image of zebrafish was obtained based on orthogonal-polarization-gating optical coherence tomography and used to segment the yolk sac region. And ellipsoid can approximate the shape of the three-dimensional yolk sac, and the multiple parameters of volume and the three principal axes (k, l and m) can be used to quantify the yolk sac. In addition, the multiple parameters of two principal axes (l and m) and volume can distinguish the malformation from the normal controlled group. Finally, the volume malformation of the yolk sac calculated by the proposed algorithm ranges from 16.55% to 46.05%. Thus, the degree of malformation can be applied for toxicity analysis. And this method provides a potential application for an accurate judgment index for biotoxicological testing.

The migratory pathways of the cells that form the endocardium, dorsal aortae, and head vasculature in the mouse embryo.

BACKGROUND: Vasculogenesis in amniotes is often viewed as two spatially and temporally distinct processes, occurring in the yolk sac and in the embryo. However, the spatial origins of the cells that form the primary intra-embryonic vasculature remain uncertain. In particular, do they obtain their haemato-endothelial cell fate in situ, or do they migrate from elsewhere? Recently developed imaging techniques, together with new Tal1 and existing Flk1 reporter mouse lines, have allowed us to investigate this question directly, by visualising cell trajectories live and in three dimensions. RESULTS: We describe the pathways that cells follow to form the primary embryonic circulatory system in the mouse embryo. In particular, we show that Tal1-positive cells migrate from within the yolk sac, at its distal border, to contribute to the endocardium, dorsal aortae and head vasculature. Other Tal1 positive cells, similarly activated within the yolk sac, contribute to the yolk sac vasculature. Using single-cell transcriptomics and our imaging, we identify VEGF and Apela as potential chemo-attractants that may regulate the migration into the embryo. The dorsal aortae and head vasculature are known sites of secondary haematopoiesis; given the common origins that we observe, we investigate whether this is also the case for the endocardium. We discover cells budding from the wall of the endocardium with high Tal1 expression and diminished Flk1 expression, indicative of an endothelial to haematopoietic transition. CONCLUSIONS: In contrast to the view that the yolk sac and embryonic circulatory systems form by two separate processes, our results indicate that Tal1-positive cells from the yolk sac contribute to both vascular systems. It may be that initial Tal1 activation in these cells is through a common mechanism.

Evaluating the Transvaginal Ultrasound Diagnostic Criteria for Abnormal First-Trimester Pregnancy With Follow-Up Into the Third Trimester and Validation of Results.

OBJECTIVE: To evaluate the current ultrasound diagnostic criteria for non-viable pregnancy in the first trimester. METHODS: We conducted a retrospective chart review involving 3 tertiary care institutions. Consecutive first-trimester ultrasound reports between January 2013 and June 2016 were reviewed. All first-trimester ultrasound examinations performed to assess pregnancy viability with adequate imaging or clinical follow-up were included. Inclusion criteria based on follow-up were adequate imaging to document ongoing intrauterine pregnancy or clinical follow-up demonstrating viability or non-viability. Data on mean sac diameter (MSD), yolk sac presence/diameter, embryo presence/length, presence of a heartbeat, and heart rate were collected. This was followed by a retrospective validation review of another consecutive cohort. RESULTS: Two hundred and forty-five examinations with a viable-pregnancy outcome and 301 examinations with a non-viable pregnancy outcome were reviewed. The main predictor of non-viable pregnancy was an MSD of ≥20 mm in the absence of a yolk sac (positive predictive value [PPV] 100%; 95% CI 93%-100%), embryo (PPV 100%; 95% CI 90%-100%), or heartbeat (PPV 100%; 95% CI 96%-100%]). Other predictors of non-viability were a measurable embryo without a yolk sac (PPV 100%; 95% CI 91%-100%), yolk sac diameter ≥8 mm (PPV 100%; 95% CI 91%-100%), and absence of heartbeat with an embryo ≥3 mm (PPV 100%; 95% CI 97%-100%). These findings were confirmed in a validation cohort of 45 viable and 53 non-viable pregnancies, with the exception of 1 case of viable pregnancy with no heartbeat and an embryo length 3.3 mm. Based on the median daily growth of 1.2 mm in the viable cohort, 21% of follow-up ultrasound examinations were performed too early for an MSD threshold of 20 mm and 55%, for an MSD threshold of 25 mm. CONCLUSION: In our cohort, MSD ≥20 mm in the absence of yolk sac or an embryo with heartbeat always predicted a non-viable pregnancy.

The Yolk Sac of the Equine Placenta. Its Remnant and Potential Problems.

This review details the current state of knowledge about the equine yolk sac and its remnant (YSR) in the pregnant mare, which, incidentally, is the only animal species known to exhibit large and/or ossified YSR. It also describes the clinical significance of the YSR and details a case of a strangulating YSR that caused fetal death and abortion.

Fetal sex prediction measuring yolk sac size and yolk sac-fetal pole distance in the first trimester via ultrasound screening.

PURPOSE: The aim of the study was to determine the accuracy of fetal sex definition by measuring the yolk sac size and the yolk sac-fetal pole distance in the first trimester via ultrasound (US) screening. METHODS: We enrolled 92 gestational women in this prospective study. In the first trimester of US examination, the gestational sac, the gestational sac-fetal pole distance, and the yolk sac size were measured. When the fetal pole was in the longitudinal position, the distance between the fetal pole and the yolk sac was measured in millimeters (mm). The crown-rump length (CRL) was measured in the same position. US examination at 22 weeks was performed to determine whether the fetal gender was male or female. The genders of the fetuses were recorded. The sexes were also confirmed and recorded after birth. RESULTS: Fifty-five (59.8%) of the newborns were found to be male, while 37 (40.2%) of them were found to be female. We compared the yolk sac size and the yolk sac-fetal pole distance in both the female and male groups. We found that the genders showed a significant difference in terms of yolk sac-fetal pole distance, whereas the yolk sac size showed no significant difference between the genders. The optimal cutoff value of the yolk sac-fetal pole distance was 1.80 mm, with 70% sensitivity and 67% specificity for female gender prediction. The distance also showed an independent association with gender prediction in the first trimester. CONCLUSION: Yolk sac-fetal pole distance may have the potential to predict gender in the first trimester of pregnancy.

Successful treatment of non-midline primary malignant germ cell tumors with yolk sac components in neonates: report of 2 cases.

Here, the authors present 2 cases of nongerminomatous germ cell tumor (NGGCT): a neonate with a mixed malignant germ cell tumor, 5% yolk sac tumor (YST) and 95% immature teratoma components, originating from the right mesial temporal lobe; and a 2-month-old infant with a pure YST originating from the left middle cranial fossa. These tumors with yolk sac components, which are thought to have a poor prognosis, were successfully treated with complete tumor resection alone and subtotal tumor resection with chemotherapy, respectively. Event-free survival exceeds 5 years for each patient even though neither received radiotherapy. The authors highlight the role of radical surgery and the successful treatment of neonatal YST with aggressive resection (and chemotherapy in 1 case) while avoiding radiation therapy. They also report the very rare non-midline location of these neonatal NGGCTs and emphasize the importance of considering YSTs and mixed NGGCTs with YST components in the differential diagnosis of non-midline hemispheric or skull base tumors in newborns.

Prediction of pregnancy loss by early first trimester ultrasound characteristics.

BACKGROUND: Pregnancy loss prediction based on routinely measured ultrasound characteristics is generally aimed toward distinguishing nonviability. Physicians also use ultrasound indicators for patient counseling, and in some cases to decide upon the frequency of follow-up sonograms. To improve clinical utility, allocation of cut-points should be based on clinical data for multiple sonographic characteristics, be specific to gestational week, and be determined by methods that optimize prediction. OBJECTIVES: To identify routinely measured features of the early first trimester ultrasound and the gestational age-specific cut-points that are most predictive of pregnancy loss. MATERIALS AND METHODS: This was a secondary analysis of 617 pregnant women enrolled in the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial; all women had 1-2 previous pregnancy losses and no documented infertility. Each participant had a single ultrasound with a detectable fetal heartbeat between 6 weeks 0 days and 8 weeks 6 days. Cut-points for low fetal heart rate and small crown-rump length were separately defined for gestational weeks 6, 7, and 8 to optimize prediction. Identity and log-binomial regression models were used to estimate absolute and relative risks, respectively, and 95% confidence intervals between jointly categorized low fetal heart rate, small crown-rump length, and clinical pregnancy loss. Adjusted models accounted for gestational age at ultrasound in weeks. Missing data were addressed using multiple imputation. RESULTS: A total of 64 women experienced a clinical pregnancy loss following the first ultrasound (10.4%), 7 were lost to follow-up (1.1%), and 546 women (88.5%) had a live birth. Low fetal heart rate and small crown-rump length (≤122, 123, and 158 bpm; ≤6.0, 8.5, and 10.9 mm for gestational weeks 6, 7, and 8, respectively) were independent predictors of clinical pregnancy loss, with greatest risks observed for pregnancies having both characteristics (relative risk, 2.08; 95% confidence interval, 1.24-2.91). The combination of low fetal heart rate and small crown-rump length was linked to a 16% (95% confidence interval, 9.1-23%) adjusted absolute increase in risk of subsequent loss, from 5.0% (95% confidence interval, 1.5-8.5%) to 21% (95% confidence interval, 15-27%). Abnormal yolk sac diameter or the presence of a subchorionic hemmhorage did not improve prediction of clinical pregnancy loss. CONCLUSION: Identified cut-points can be used by physicians for patient counseling, and in some cases to decide upon the frequency of follow-up sonograms. The specified criteria should not be used to diagnose nonviability.

"Pseudogestational Sac" and Other 1980s-Era Concepts in Early First-Trimester Ultrasound: Are They Still Relevant Today?

OBJECTIVES: To determine whether an intrauterine round or oval fluid collection ("saclike structure") can prove to be either an intrauterine pregnancy or intrauterine fluid in conjunction with an ectopic pregnancy (sometimes termed "pseudogestational sac") and whether ultrasound features, including the presence or absence of an echogenic rim, "double sac sign" (DSS), or "intradecidual sign" (IDS), are helpful for establishing the diagnosis or predicting the prognosis. METHODS: We identified all sonograms obtained from women with positive serum human chorionic gonadotropin results at our institution between January 1, 2012, and June 30, 2018, meeting the following criteria: presence of an intrauterine saclike structure without a yolk sac or embryo; no extraovarian adnexal mass; and follow-up information identifying the location of the pregnancy as intrauterine or ectopic. Study authors reviewed sonograms in all cases and recorded the following information: presence or absence of each of an echogenic rim around the collection, a DSS, and an IDS, as well as the mean sac diameter. The indications for the initial ultrasound examinations were recorded. RESULTS: A total of 649 sonograms met the inclusion criteria. Of these, 598 fluid collections showed an echogenic rim, 182 a DSS, and 347 an IDS (findings not mutually exclusive). In all 649 cases, a subsequent sonogram or other clinical follow-up confirmed that the patient had an intrauterine pregnancy. That is, none of the fluid collections proved to be a pseudogestational sac. In total, 41.2% were live at the end of the first trimester, and 58.8% miscarried. The prognosis was better in cases with, compared to without, an IDS (P = .01, χ2 ), but no ultrasound feature was clinically useful for ruling in or excluding a good prognosis. CONCLUSIONS: In a woman with positive human chorionic gonadotropin results and no extraovarian adnexal mass, the ultrasound finding of an intrauterine saclike structure is virtually certain to be a gestational sac. Ultrasound features of the structure are of no diagnostic or clinically useful prognostic value. Concepts introduced 30 to 40 years ago when ultrasound equipment had far lower resolution than currently, including a DDS, an IDS, and a pseudogestational sac, have no role today in assessing early pregnancy.

Pilot study establishing a nomogram of yolk sac growth during the first trimester of pregnancy.

AIM: The yolk sac (YS) has been reported as a reliable predictor of adverse pregnancy outcomes, however, it has always been evaluated cross-sectionally with a single ultrasound per patient. We sought to validate the use of YS dimensions in serial ultrasounds throughout the first 10 weeks of singleton and multiple gestations. METHODS: This was a prospective cohort study where YS diameters were serially obtained with 2D ultrasound in singleton and multiple gestations from 5 to 11 weeks. Nonparametric test were used for comparisons with P < 0.05 indicating significance. RESULTS: One hundred ninety-three patients were included, 42 twins (3 monochorionic and 39 dichorionic), 2 triplets (monochorionic twins plus a singleton) and 148 singleton pregnancies (238 total fetuses). There was no difference in YS dimensions in singleton versus multiple pregnancies. Starting at 5 weeks' gestation, the YS increased 0.4 mm (95% CI 0.3-0.5 mm) per week until 10 weeks' gestation. Forty-five fetuses were lost in the first trimester. The risk of pregnancy loss was higher with a large YS until 8 weeks (P ≤ 0.001), while after 8 weeks it was higher with a small YS (P < 0.005). CONCLUSION: We established a nomogram of YS development during the first 10 weeks of pregnancy. The YS reliably detected pregnancies that ended in loss as early as 6 weeks' gestation. The YS was either smaller or larger than in ongoing pregnancies. While all pregnancies with large YS were lost within 10 weeks, those with smaller YS were lost beyond the first 10 weeks.

Progesterone's Serum Level and a New Ultrasonographic Parameter in the First Trimester Pregnancy - Prognostic Factors for Embryonic Demise.

OBJECTIVE: The etiology of embryonic demise is multifactorial, with chromosomal abnormalities being the most common (40%). The purpose of the present study is to evaluate the correlation between a serum biomarker, progesterone, and an ultrasonographic parameter, the distance between yolk sac and embryo (DYSE) in assessing the prognosis of pregnancy outcome in the 1st trimester. METHODS: The present study is a prospective case-control analysis that includes 2 groups of patients: 81 patients with first-trimester normal evolutive pregnancy and 89 patients with embryonic demise, all of the patients having between 6 and 11 weeks of amenorrhea. Endovaginal ultrasonographic exploration was performed to evaluate the distance between the lower pole of the embryo and the yolk sac. From each subject enrolled in the study, 20 ml of blood was collected for progesterone serum level measurement. RESULTS: Regarding the DYSE in the case group, lower values were observed compared with the control group, the difference being statistically significant. In the statistical analysis of serum progesterone values, statistically significant differences were observed between the 2 groups (p < 0.05). CONCLUSION: The DYSE has a high positive predictive value in identifying pregnancies with potentially reserved outcome, with the present study demonstrating that a DYSE < 3 mm causes an unfavorable evolution of the pregnancy. Low serum levels of progesterone are associated with an increased rate of nonviable embryos. The correlation between these two parameters increases the effectiveness of screening methods in prenatal monitoring and improves the diagnostic methods for the first-trimester pregnancies whose outcome potential can be reserved.

Progesterone's serum level and a new ultrasonographic parameter in the first trimester pregnancy - prognostic factors for embryonic demise

Abstract Objective The etiology of embryonic demise is multifactorial, with chromosomal abnormalities being the most common (40%). The purpose of the present study is to evaluate the correlation between a serum biomarker, progesterone, and an ultrasonographic parameter, the distance between yolk sac and embryo (DYSE) in assessing the prognosis of pregnancy outcome in the 1st trimester. Methods The present study is a prospective case-control analysis that includes 2 groups of patients: 81 patients with first-trimester normal evolutive pregnancy and 89 patients with embryonic demise, all of the patients having between 6 and 11 weeks of amenorrhea. Endovaginal ultrasonographic exploration was performed to evaluate the distance between the lower pole of the embryo and the yolk sac. From each subject enrolled in the study, 20ml of blood was collected for progesterone serum level measurement. Results Regarding the DYSE in the case group, lower values were observed compared with the control group, the difference being statistically significant. In the statistical analysis of serum progesterone values, statistically significant differences were observed between the 2 groups (p<0.05). Conclusion The DYSE has a high positive predictive value in identifying pregnancies with potentially reserved outcome, with the present study demonstrating that a DYSE<3mm causes an unfavorable evolution of the pregnancy. Low serum levels of progesterone are associated with an increased rate of nonviable embryos. The correlation between these two parameters increases the effectiveness of screening methods in prenatal monitoring and improves the diagnostic methods for the firsttrimester pregnancies whose outcome potential can be reserved.

The Significance of Yolk Sac Number in Monoamniotic Twins.

BACKGROUND: Detection of a single yolk sac on early first trimester ultrasound was previously thought to be a reliable diagnostic feature of monochorionic monoamniotic (MCMA) twin pregnancies. OBJECTIVES: To determine the frequency of two yolk sacs in MCMA twin pregnancies and the association of yolk sac number with pregnancy outcomes. METHODS: A retrospective cohort analysis of MCMA twins managed at a tertiary obstetric centre from January 2003 until February 2017. All MCMA twin pregnancies were diagnosed on tertiary centre ultrasound and, where possible, placental histopathology postnatally. All MCMA twin pregnancies, including conjoined twins, with available first trimester ultrasounds from 5 to 11 weeks' gestation were included in the analysis. MCMA pregnancies without available first trimester ultrasounds and triplet pregnancies which included a MCMA pair were excluded from the study. RESULTS: Sixty-seven MCMA cases were identified over 14 years. Thirty-eight cases were included in the analysis. There was one yolk sac identified in 26 cases (68%) and two yolk sacs in 12 cases (32%). Two yolk sacs were associated with a higher proportion of male fetuses (33%, 4 out of 12, vs. 8%, 2 out of 26; p = 0.01). There were no other significant differences between one and two yolk sacs for maternal or neonatal outcomes. CONCLUSIONS: Two yolk sacs are present in up to a third of all MCMA twin pregnancies, dispelling the original concept that a single yolk sac is diagnostic of MCMA pregnancies. Yolk sac number should not be used to determine amnionicity. The presence of two yolk sacs on first trimester ultrasound is associated with an increased rate of male fetuses. The number of yolk sacs has no other significant impact on perinatal outcomes.

The human yolk sac size reflects involvement in embryonic and fetal growth regulation.

INTRODUCTION: The human yolk sac provides the embryo with stem cells, nutrients, and gas exchange. We hypothesized that more maternal resources, reflected in body size and body composition, would condition a a larger yolk sac, ensuring resources for the growing embryo. Thus, we aimed to determine the relation between maternal size in early pregnancy and yolk sac size. MATERIAL AND METHODS: This subsidiary study was embedded in the multinational World Health Organization fetal growth project that included healthy women with a body mass index of 18-30, reliable information of their regular last menstrual period and singleton pregnancies. Yolk sac diameter, crown-rump length, and maternal height, weight, body mass index, and body composition were assessed before 13 weeks of gestation, and the fetal biometry was repeated during the pregnancy. RESULTS: Of 140 participants, 122 with a successful yolk sac measurement were entered in the present analysis. Maternal weight was negatively associated with the yolk sac diameter (P = 0.007) and so was maternal height (P = 0.011), fat mass (P = 0.037), and lean body mass (P = 0.018), but not body mass index (P = 0.121). Significant effects were predominantly due to the female embryos and could be traced at 24 weeks of gestation. That is, a small yolk sac : crown-rump length ratio in early pregnancy was associated with a high fetal abdominal circumference (P < 0.001) and estimated fetal weight (P = 0.001). CONCLUSIONS: The human yolk sac is involved in the regulation of embryonic growth, but contrary to our hypothesis, the yolk sac has a compensatory capacity, being larger when the mothers are smaller; and the effect can be traced on fetal size at 24 weeks of gestation.

Yolk sac size & shape as predictors of first trimester pregnancy outcome: A prospective observational study.

OBJECTIVE: To determine the value of yolk sac size and shape for prediction of pregnancy outcome in the first trimester. MATERIAL AND METHODS: 500 pregnant women between 6+0 and 9+6 weeks of gestation underwent transvaginal ultrasound and yolk sac diameter (YSD), gestational sac diameter (GSD) were measured, presence/absence of yolk sac (YS) and shape of the yolk sac were noted. Follow up ultrasound was done to confirm fetal well-being between 11+0 and 12+6 weeks and was the cutoff point of success of pregnancy. RESULTS: Out of 500 cases, 8 were lost to follow up, YS was absent in 14, of which 8 were anembryonic pregnancies. Thus, 478 out of 492 followed up cases were analyzed for YS shape and size and association with the pregnancy outcome. In our study, abnormal yolk sac shape had a sensitivity and specificity (87.06% & 86.5% respectively, positive predictive value (PPV) of 58.2%, negative predictive value (NPV) of 96.8% in predicting a poor pregnancy outcome as compared to yolk sac diameter (sensitivity and specificity 62.3% & 64.1% respectively and PPV and NPV of 27.3% and 88.7% respectively). The degree of association for both the variables was significant to the level of p<0.000. CONCLUSION: The presence or absence of yolk sac has a strong predictive value for poor pregnancy outcome. Yolk sac shape was a better predictor of poor pregnancy outcome in terms of higher specificity and negative predictive value as compared to yolk sac diameter.

Yolk sac-embryo distance in correlation with soluble form of vascular endothelial growth factor levels in pregnancy with potentially reserved evolutivity.

AIMS: Embryonic demise is a frequent complication of the first trimester pregnancy. The purpose of this study was to evaluate the correlation between a serum biomarker, the soluble form of the vasculo-endothelial growth factor (sFlt-1) and the distance between the yolk sac (YS) and embryo (DYSE), determined by ultrasonography. MATERIAL AND METHODS: The study was a prospective case-control study that included 2 groups of patients - the control group with 81 first-trimester pregnancies in evolution and the case group with 89 first-trimester pregnancies with a potentially reserved evolutivity. RESULTS: A correlation between the serum level of sFlt-1 and DYSE in embryos with crown-rump length (CRL) greater than 5 mm was identified, showing that a DYSE ≤3 mm correlates with a low level of sFlt-1 (p<0.05) and a DYSE> 4 mm correlates with an increased level of sFlt-1 (p<0.05). CONCLUSIONS: A low level of sFlt-1 associated with a distance between the embryo and yolk sac of small dimensions, respectively <3 mm, correlates with an increased rate of non-viable embryos. This correlation between an ultrasound and a serum parameter is of great value and brings important information about the viability of firsttrimester pregnancies.

Endoscopy, histology and electron microscopy analysis of foetal membranes in pregnant South American plains vizcacha reveal unusual excrescences on the yolk sac.

The South American hystricognathe Lagostomus maximus is a fossorial rodent whose females show unique reproductive characteristics. They have a 155-day long gestation, show massive polyovulation and a selective process of embryonic resorption in the first half of gestation. In order to explore and perform an in-situ characterization of the reproductive tract, we visualized internal structures through ultrasonography and video-endoscopy in pregnant and non-pregnant females. We describe the finding of protruding structures that lie on the yolk sac and their histological and ultrastructural characterization. The placenta was covered with whitish, small pearl-shaped structures. These structures were also seen on the extra-embryonic space, being the amnion and the umbilical cord free of them. Pearl-shaped structures were composed with loose connective tissue, lacked blood vessels, and showed collagen fibers organized in a spiral form. They were anchored by pedicles to the villous surface of the extraembryonic membrane. We discuss the biological and evolutionary meaning of the pearl-shaped structures that relate L. maximus to the African origin of the South American hystricognathe fauna.