Number Of Yolk Sacs Research Articles

Determining chorionicity and amnionicity in twin pregnancies: Pitfalls.

Although the accuracy of chorioamnionicity determination in multiple pregnancy is nearly 100%, some pitfalls do exist. These pitfalls may arise from some confusing sonographic appearance or because of certain rare variations of twinning going against the general principles. Pitfalls in chorionicity determination include (1) the disappearance of the twin peak sign with the regression of chorion frondosum and thinning of the intertwin membrane with advancing gestation; (2) fake twin peak sign because of other structures creeping into the intertwin membrane-placental junction; (3) intrauterine septum or synechia being mistaken as a thick intertwin membrane; (4) bipartite placenta in monochorionic twin being misinterpreted as two separate placentas of dichorionic twin; (5) erroneous fetal sex determination in sex chromosome mosaicism, monogenic disorders, and malformed genitalia in one fetus; and (6) rare twinning types such as dizygotic monochorionic twin and sesquizygotic twin. Pitfalls in amnionicity determination are (1) the lack of correlation between the number of yolk sacs and amnionicity and (2) failure to visualize the intertwin membrane because of technical issues.

Three-dimensional ultrasonographic features of diamniotic conjoined twins with body stalk anomaly

BackgroundSince conjoined twins were thought to be monoamniotic in the past, diamniotic conjoined twins would be improbable theoretically. Body stalk anomaly is a severe defect of the body wall, which is rare among twins. Body stalk anomaly in monochorionic diamniotic conjoined twins has never been reported prenatally so far as we know.Case presentationHere we present an extremely rare case of concordant body stalk anomaly in monochorionic diamniotic conjoined twins. Ultrasonography at 9 + 5 weeks revealed one chorionic and two amniotic cavities, close apposition of abdomen, limited movement, and common umbilical vessels. Follow-up ultrasonography at 11 + 6 weeks and 13 + 2 weeks showed close apposition of the lower abdominal region with cystic structures and a small bowel-like mass between the two fetuses. Three-dimensional ultrasonography assisted in observing the entire appearance of both twins in earlier first trimester, including amnioticity, conjoined region and umbilical vessels. We attribute this diamniotic conjoined twin in our case to the fusion theory. A single yolk sac was observed, challenging the idea that yolk sac number predicts amnionicity. Identification of single yolk sac and its allantois may form a common body stalk during this fusion, leading to concordant body stalk anomaly in monochorionic diamniotic twins.ConclusionsOur case may provide important insights into both ultrasonographic features and embryogenesis of this extremely rare anomaly.

Prediction of Amnionicity Using the Number of Yolk Sacs in Monochorionic Multifetal Pregnancy.

The purpose of this article was to evaluate the accuracy of predicting amnionicity using the number of yolk sacs by diagnostic ultrasound examination in monochorionic (MC) multifetal pregnancies between 7 + 0 and 9 + 6 gestational weeks. A total of 97 patients with MC multifetal pregnancies underwent early ultrasound examination from 2004 to 2014 at Cheil General Hospital and Women's Healthcare Center. All patients for whom the number of yolk sacs was reported were included in this study. We compared the number of yolk sacs with amnionicity confirmed by an intertwine membrane. Overall, there was a 9.3% (9 cases) discrepancy in number of yolk sacs and amnionicity (4.3% for monochorionic diamniotic, 36.4% for monochorionic monoamniotic, and 33% for monochorionic triamniotic). Among the 9 cases with discrepancies, 4 cases with 2 yolk sacs were confirmed as monoamniotic pregnancies and 4 MC twin pregnancies showing a single yolk sac were diagnosed as diamniotic twin pregnancies. One case with 2 yolk sacs was identified as a triamniotic triplet pregnancy. In 9.3% of MC gestations, the number of yolk sacs was not correlated with the number of amnions in our study. To determine amnionicity in MC multifetal pregnancies, we recommend careful evaluation not of the number of yolk sacs but the presence or absence of intertwine dividing membrane after 8 gestational weeks.

The impact of sheep grazing on the fecundity and timing of reproduction in the endangered pygmy bluetongue lizard, Tiliqua adelaidensis

The endangered pygmy bluetongue lizard (Tiliqua adelaidensis) is found only in a few remaining patches of South Australian native grassland, most of which are used for live stock grazing. The lizards occupy spider burrows, they mate in October-November and females produce litters of one to four live born neonates in mid-January-mid-March. In this study we use ultrasound scans of females and observations of neonates in their maternal burrows to investigate how grazing affects the fecundity of the pygmy bluetongue lizard. We predicted that lizards in moderately grazed paddocks would have a higher reproductive output than lizards in hard grazed paddocks. Ultrasound scans indicated that this hypothesis was correct by showing a higher mean number of yolk sacs in females from moderately than from hard grazed paddocks. Females from moderately grazed paddocks also gave birth significantly earlier than females in hard grazed paddocks. The higher number of yolk sacs did not result in a significantly higher number of neonates observed in the burrows, which indicates that the weekly burrow observations used in this study may underestimate true fecundity. Understanding how grazing affects the fecundity of the pygmy bluetongue lizard is essential to the future management of this endangered species. This is not only because grazing is used to manage the habitat of all currently known lizard populations, but also because successful reproduction will be needed in those populations to supply the “surplus” individuals predicted to be essential for relocation programs to ensure the survival of the species.

Yolk sac number does not predict reliably amnionicity in monochorionic twin pregnancies: a case of a monochorionic monoamniotic twin pregnancy with two distinct yolk sacs on early first‐trimester ultrasound

The dramatic increase in multiple births over the past 30 years has made multiple pregnancy one of the most common high-risk conditions encountered by obstetricians. In North America, the rate of multiple pregnancy has increased by 50–70% and this is largely attributed to advanced reproductive technologies1, 2. In monochorionic multiple gestations the determination of amnionicity is technically difficult to perform based both on the relatively late appearance of the amnion on ultrasound, typically between 8 and 10 weeks, along with the thin nature of the membrane. Previous studies have suggested that on early first-trimester ultrasound, monochorionic monoamniotic (MCMA) twin pregnancies can be reliably characterized by the presence of a single yolk sac and monochorionic diamniotic (MCDA) twins can be reliably characterized by the identification of two yolk sacs3. Accurate and early prenatal ultrasound diagnosis of amnionicity, along with enhanced prenatal/neonatal care, has been shown to decrease the mortality rates of MCMA twins from 50% to 10–20% in more recent years2. Recently, the accuracy of using yolk sac number as a means of predicting amnionicity has been challenged4-6. In a recent series of 22 cases of monochorionic multiple gestations, Shen et al.4 revealed that 85% of the 20 cases of MCDA gestations had two yolk sacs and that 15% were characterized by only a single yolk sac; a single case of MCMA was identified in this series and one yolk sac was seen. In 2010, three cases of MCMA twins characterized by the presence of two yolk sacs on first-trimester ultrasound were reported5, 6. Here, we present a fourth case of MCMA twins in which early first-trimester ultrasound demonstrated the presence of two yolks sacs with confirmed monoamnionicity in the late first trimester. A 31-year-old G1P0 Caucasian woman presented at a private fertility clinic for intrauterine insemination with donor sperm for social reasons. A transvaginal ultrasound examination (E8, GE Medical Systems, Zipf, Austria) was performed at 7 + 0 weeks for confirmation of intrauterine pregnancy. The 7-week ultrasound clearly demonstrated two distinct fetal poles and two separate yolk sacs. The crown–rump length measurements, of 7.6 mm and 7.9 mm, were consistent with the expected size for each fetal pole, and cardiac activity was present in both. The pregnancy was considered to be MCDA twin gestation at this point in time, based on the presence of two yolk sacs (Figure 1). At 9 + 2 weeks a single amniotic sac was observed with the absence of a dividing intergestational membrane (Figure 2). At 12 + 2 weeks of gestation, ultrasound demonstrated the absence of a dividing membrane between the fetuses (Figure 3). Power Doppler at this time revealed umbilical cord entanglement, confirming the diagnosis of a MCMA twin gestation (Figure 4). Transvaginal ultrasound at 7 weeks' gestation demonstrated two yolk sacs in a monochorionic twin pregnancy. Repeat transvaginal ultrasound at 9 + 2 weeks revealed a single amniotic sac and the absence of an intergestational membrane. Transvaginal ultrasound at 12 + 2 weeks demonstrated the absence of a dividing membrane. Transvaginal ultrasound at 12 + 2 weeks verified umbilical cord entanglement. This case highlights the close proximity in the sequence of development of the yolk sac and amnion and emphasizes our lack of understanding of the temporal differentiation of these structures. The almost simultaneous development of the yolk sac and amnion could explain these most recent findings that yolk sac number does not always correlate with amnionicity in monochorionic gestations. Yolk sac number should no longer be considered a reliable means of diagnosing amnionicity on early first-trimester ultrasound. The consequent clinical implications are an enhanced focus on the diagnosis of amnionicity based on the presence or absence of the intergestational amnion and the visualization of umbilical cord entanglement7, 8.

OP19.05: Monochorionic monoamniotic twin pregnancies with two yolk sacs may not be a rare finding: a report of two cases

Exact determination of amnionicity is a major issue for clinical management of monochorionic twin pregnancies, due to quite high risk of perinatal mortality and morbidity in monochorionic monoamniotic (MM) twins. Counting the number of yolk sacs is believed to be good indicator of amnionicity in the early first trimester, as the number of yolk sacs is alleged to be equal to amnionicity order in both MM and monochorionic diamniotic (MD) twin pregnancies. However, the accuracy of the relationship between number of yolk sacs and amnionicity has recently been called into question in MD twin pregnancies. To the best of our knowledge, no previous reports have shown two yolk sacs in MM twin pregnancies. We report 2 cases of MM twins with two yolk sacs on first trimester ultrasonography, and confirmed monoamnionicity showing umbilical cord entanglement and postnatal placental examination. Pregnant courses of both cases were uneventful, and elective Cesarean sections were performed at 33 + 2 and 34 + 4 weeks of gestation, respectively. All four babies showed good growth without any complications by 2 years old and 4 months old in each. Amnionicity of both cases were also confirmed MM twin placenta after postnatal gross examinations. In conclusion, two yolk sacs in cases of MM twin pregnancy may not be a rare finding and can be expected to show equivalent outcomes to MM twin pregnancy with a single yolk sac. Detection of two yolk sacs on ultrasound examination in monochorionic twin pregnancy does not rule out monoamnionicity. The possibility of monoamnionicity must still be suspected when two yolk sacs are detected early in the first trimester ultrasound examination for monochorionic twin pregnancies.

Monochorionic monoamniotic twin pregnancies with two yolk sacs may not be a rare finding: a report of two cases

The exact determination of amnionicity is a major issue for the clinical management of monochorionic twin pregnancies, due to the high risk of perinatal mortality and morbidity in monochorionic monoamniotic (MCMA) twins. Counting the number of yolk sacs is believed to be a good indicator of amnionicity in the early first trimester, and it has previously been suggested that the number of yolk sacs is equal to amnionicity in both MCMA and monochorionic diamniotic twin pregnancies. However, the accuracy of the relationship between number of yolk sacs and amnionicity has recently been called into question. To the best of our knowledge, no previous reports have shown two yolk sacs in MCMA twin pregnancies. We report two cases of MCMA twins with two yolk sacs on first-trimester ultrasonography, and confirmed monoamnionicity in the second trimester showing umbilical cord entanglement. Postnatal examination showed an MCMA placenta in both cases, and entangled umbilical cords confirmed monoamnionicity. The possibility of monoamnionicity must still be suspected when two yolk sacs are detected early in the first trimester on ultrasound examination in monochorionic twin pregnancies.

Starting point and obstetric outcome of monochorionic twinning (MCT). Spontaneous vs. IVF pregnacies

OBJECTIVE: Evaluate early diagnosis (ED) of amnionicity(AMN), obstetric outcome (ObO), and its relationship with ART of MCT. DESIGN: Prospective, controlled study. MATERIALS AND METHODS: 13313 first trimester pregnancies were evaluated by transvaginal ultrasound (TV-US): 1447 following ART, of which 37 were blastocyst transfers (BT); and 11866 spontaneous (SP). 57 MCT were followed. Two groups were formed; GrI: 26 cases from ART, 2 resulting from BT; GrII: 31 cases from SP. To presume AMN the number of yolk sacs (YS) was correlated with the number of amnions in a MCT. Incidence (IN), age of patients(AOP), AMN, and ObO were evaluated. Wilcoxon and Fisher's Test were used. RESULTS: The IN of MCT was 17,9‰ in GrI vs 2,6‰ in GrII (P< 0,001). AOP in GrI: 34,7 ± 3,22 vs 30,7 ± 4,27 in GrII (P<0,04). In GrI, of 37 BT, 2 ended MCT(54,1‰), the remaining 24 MCT from 1410 cleavage ET(17‰). 17 were twin, 6 triplets, 2 quadruplets and 1 quintuplet. In GrII, 28 were twins and 3 triplets. Each one with a MCT. 50 cases were seen before 8 weeks and the number of YS correlated with AMN. Monoamniotic IN in Gr I: 11,5%(3/26) vs 13% (4/31) in GrII(NS). Abortion: 27%(7/26) in GrI vs 42%(13/31) in Gr II(NS). Two liveborns: GR I: 52% (13/25) vs 53% (16/30) in Gr II (NS). One liveborn: Gr I: 8% (2/25) vs 3% (1/30) in Gr II (NS). In GrI FGR in both: 16% (4/25) vs 17% (5/30) in GrII (NS). FGR in 1 fetus: 16% (4/25) in Gr I vs 7% (2/30) in GrII(NS). Prematurity: 44% (11/25) in GrI vs 30% (9/30) in GrII (NS). Discordant growth: 20% (5/25) for GrI and 13(4/30) for GrII(NS). PPROM: 20% (5/25) in GrI vs 17%(5/30) in GrII(NS). T-TTS: 8%(2/25) in GrI vs. 3%(1/30) in GRII(NS). Malformations in GrI: 12% (3/25) vs.13% (4/31) in GrII, (NS). Fetal death: 12% (3/25) in GrI vs. 3% (1/30) in GrII(NS). Still one ongoing pregnancy in each group. CONCLUSION: ED of MCT and its AMN is possible before 8 weeks by TV-US. MCT shows higher rates in ART group. BT seems to increase the IN of MCT. No significant differences were found in obstetric outcome between groups.

Yolk-Sac Number in Monoamniotic Twins

It has been accepted practice to use yolk-sac number to predict amnionicity in twin pairs. Two yolk sacs in a single chorionic sac were thought to confirm diamniotic pregnancy, and a single yolk sac with two fetal poles was thought to indicate monoamniotic twins. Thus, basic ultrasonography could confirm amnionicity early in pregnancy and avoid invasive testing or the more difficult tasks of demonstrating the absence of a dividing membrane or presence of entwined cords later in the pregnancy. We present a case of monoamniotic twin gestation in which early ultrasonography confirmed the presence of two yolk sacs. Doppler showed entwined umbilical cords. After elective cesarean delivery, the twins did well in the neonatal intensive care unit and continue to thrive. Yolk-sac number does not predict amnionicity. The diagnosis of monoamniotic twins requires demonstration of entwined cords or an invasive procedure.

Monozygotic twinning: A 5 year experience in a large IVF center doing blastocyst transfers on day 5

Monozygotic twinning (MZ) is estimated to occur in 3–4/1000 live births. Up to a 4-fold increase in MZ has been reported after ART. Our objective is to assess MZ incidence, chorionicity and amnionicity following IVF using autologous and donor eggs. Retrospective review of all IVF cycles from 2000–2004 at a university-based infertility center. When patients were subjected to an early 1st trimester transvaginal ultrasound (TVU), MZ was suspected if there were 2 fetal poles in a gestational sac or the total number of yolk sacs, fetal poles or heartbeats exceeded the number of embryos transferred. When MZ was suspected, a follow-up TVU was done 2–4 weeks later to assess fetal viability and scan for a dividing membrane in sacs with >1 fetus; if seen, the placentation was monochorionic-diamniotic (M-D); if not, it was monochorionic-monamniotic (M-M). When the number of gestational sacs exceeded the number of embryos replaced, the pregnancy was dichorionic-diamniotic (D-D). Delivery outcome was assessed. 6,668 patients conceived 2866 pregnancies of which 67 were MZ: 47 and 20 followed embryo transfer (ET) of autologous (mean age 36 ± 4) and donor oocytes. Fourteen occurred post-day 3 ET and 53 post-day 5 ET. A follow-up TVU was performed in 43 patients: 37 (86%) were M-D, 5 (12%) were D-D, and only 1 (2%) was M-M. Nine women elected to reduce the MZ fetus pair; the M-D pregnancy had umbilical cord ligation of a single twin. One or more liveborns were delivered in 84% of the MZ pregnancies. Only 26 of 86 fetuses in the MZ sets, all M-D, were born live, including 7 fetuses remaining as part of a MZ pair. 14 MZ twins were spontaneously lost in women who also had another fetus in utero and this singleton was delivered alive. Seven patients underwent therapeutic abortion for chromosomal abnormalities. In this review, 86% of MZ pregnancies were M-D and only 1 was M-M. These findings contrast with Alikani's (2003) report that 37% of MZ were M-M. This clinic-to-clinic M-M difference is difficult to explain. Our results suggest that, although the overall incidence of MZ increases with ART (and more specifically with blastocyst culture), the incidence of M-M does not increase over that reported for naturally conceived MZ gestations. Finally, that we did not visualize embryo splitting throughout culture to Day 5, questions whether MZ splitting for a D-D or M-D pregnancy occurs during this period.

Uterine receptivity and the two and three dimensions of ultrasound

Uterine receptivity and the two and three dimensions of ultrasound

Number of yolk sacs does not predict amnionicity in early first‐trimester monochorionic multiple gestations

To determine the relationship between amnionicity and number of yolk sacs before 11 weeks of gestation. Twenty-two cases of monochorionic multiple pregnancy were scanned before 11 weeks of gestation. There were 21 sets of twins and one of triplets. Amnionicity was determined by visualization of a dividing amniotic membrane between the gestational sacs. The number of yolk sacs was recorded and compared with the presence or absence of a dividing membrane for all fetuses. In 17/20 (85%) cases of monochorionic diamniotic twins, two yolk sacs were seen. In 3/20 (15%) cases of monochorionic diamniotic twins, a single yolk sac was seen. In the one case of monochorionic diamniotic triplets, two yolk sacs were visualized. In one case of monoamniotic twins, a single yolk sac was observed. In monochorionic pregnancies, the presence of two yolk sacs predicts diamnionicity. However, the use of the number of yolk sacs as a predictor of amnionicity may not be accurate in a small proportion of patients. The diagnosis of monoamnionicity can be made only following a careful search for a dividing amniotic membrane.

P06.02: Number of yolk sacs does not predict amnionicity in early first trimester monochorionic multiple gestations

P06.02: Number of yolk sacs does not predict amnionicity in early first trimester monochorionic multiple gestations

Using the number of yolk sacs to determine amnionicity in early first trimester monochorionic twins.

The purpose of this study was to evaluate the relationship between the number of yolk sacs and amnionicity in monochorionic twin pregnancies scanned early in the first trimester. We retrospectively reviewed images of all monochorionic twins scanned between 6 and 9.5 weeks' gestation and with pathologic or sonographic confirmation of chorionicity-amnionicity. Each film was reviewed for the number of yolk sacs present, as well as for the gestational age at which the amniotic membrane was first visualized. Twenty monochorionic-diamniotic pregnancies and two monochorionic-monoamniotic pregnancies met the criteria for inclusion in the study. In diamniotic pregnancies scanned at less than 8 weeks' gestation, only the yolk sacs were identified; none of the dividing amniotic membranes were detected. Two yolk sacs were identified in all but one case. In this case, although one yolk sac was seen at 6 weeks, follow-up scanning at 8 weeks revealed two yolk sacs. In each of the monochorionic-monoamniotic twin pregnancies, one yolk sac was seen at 9 weeks and a single amnion encircled both embryos. We conclude that the sonographic identification of two yolk scas in monochorionic twins enables us to make the diagnosis of diamniotic twins early in the first trimester, before the amniotic membrane can be imaged. The presence of one yolk sac should prompt a follow-up ultrasonogram to assign amnionicity definitively.