21.
Models for achromatic light-curve breaks in gamma-ray burst afterglows: jets, structured outflows and energy injection
Panaitescu, A.
Monthly notices of the Royal Astronomical Society,
09/2005, Volume:
362, Issue:
3
Journal Article
The steepening (break) of the power-law fall-off observed in the optical emission of some gamma-ray burst (GRB) afterglows at epoch ∼1 d is often attributed to a collimated outflow (jet), undergoing ...
lateral spreading. Wider opening GRB ejecta with a non-uniform energy angular distribution (structured outflows) or the cessation of energy injection in the afterglow can also yield light-curve breaks. We determine the optical and X-ray light-curve decay indices and spectral energy distribution slopes for 10 GRB afterglows with optical light-curve breaks (980519, 990123, 990510, 991216, 000301, 000926, 010222, 011211, 020813, 030226), and use these properties to test the above models for light-curve steepening. It is found that the optical breaks of six of these afterglows can be accommodated by either energy injection or by structured outflows. In the refreshed shock model, a wind-like stratification of the circumburst medium (as expected for massive stars as GRB progenitors) is slightly favoured. A spreading jet interacting with a homogeneous circumburst medium is required by the afterglows 990510, 000301, 011211 and 030226. The optical pre- and post-break decays of these four afterglows are incompatible with a wind-like medium. The current sample of 10 afterglows with breaks suggests that the distribution of the break magnitude Δα (defined as increasing the afterglow decay exponent) is bimodal, with a gap at Δα≃ 1. If true, this bimodality favours the structured outflow model, while the gap location indicates a homogeneous circumburst environment.
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22.
Impaired placentation in women with chronic hypertension who develop pre‐eclampsia
Panaitescu, A. M.; Akolekar, R.; Kametas, N. ...
Ultrasound in obstetrics & gynecology,
October 2017, 2017-Oct, 2017-10-00, 20171001, Volume:
50, Issue:
4
Journal Article
ABSTRACT
Objective
To compare the degree of impaired placentation in women with and those without chronic hypertension (CH) who develop pre‐eclampsia (PE) in pregnancy.
Methods
Data were derived from ...
prospective screening for adverse pregnancy outcomes in women with singleton pregnancy attending their first routine hospital visit at 11 + 0 to 13 + 6 weeks' gestation. This visit included recording of maternal characteristics and medical history and measurement of mean arterial pressure (MAP), uterine artery pulsatility index (UtA‐PI), serum placental growth factor (PlGF) and serum pregnancy‐associated plasma protein‐A (PAPP‐A). The measured biomarkers were converted to multiples of the median (MoM) after adjustment for pregnancy characteristics. MoM values in women with CH who developed PE (n = 283) were compared to those of women without CH who developed PE (n = 2236).
Results
In both groups with and without CH, measurements of MAP and UtA‐PI were increased, whereas those of PlGF and PAPP‐A were decreased and the deviation from normal in all biomarkers decreased with advancing gestational age at delivery with PE. There was no significant difference between women with and those without CH in the slope of the regression line of log10 MoM biomarker values against gestational age at delivery with PE for any of the biomarkers. However, there was a significant difference in the intercepts and coefficients of biomarkers in the two groups; compared to those without CH, MAP MoM, PlGF MoM and PAPP‐A MoM were higher and UtA‐PI MoM was lower in the CH group (all P < 0.01).
Conclusion
In pregnancies that develop PE, the degree of impaired placentation, reflected in high UtA‐PI and low PlGF and PAPP‐A at 11–13 weeks' gestation, is less in women with CH than in those without CH. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.
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23.
The Bright Optical Flash and Afterglow from the Gamma-Ray Burst GRB 130427A
Vestrand, W. T.; Wren, J. A.; Panaitescu, A. ...
Science,
01/2014, Volume:
343, Issue:
6166
Journal Article
The optical light generated simultaneously with x-rays and gamma rays during a gamma-ray burst (GRB) provides clues about the nature of the explosions that occur as massive stars collapse. We report ...
on the bright optical flash and fading afterglow from powerful burst GRB 130427A. The optical and >100—megaelectron volt (MeV) gamma-ray flux show a close correlation during the first 7000 seconds, which is best explained by reverse shock emission cogenerated in the relativistic burst ejecta as ft collides with surrounding material. At later times, optical observations show the emergence of emission generated by a forward shock traversing the circumburst environment The link between optical afterglow and >100-MeV emission suggests that nearby early peaked afterglows will be the best candidates for studying gamma-ray emission at energies ranging from gigaelectron volts to teraelectron volts.
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24.
Taxonomy of gamma-ray burst optical light curves: identification of a salient class of early afterglows
Panaitescu, A.; Vestrand, W. T.
Monthly Notices of the Royal Astronomical Society,
June 2008, Volume:
387, Issue:
2
Journal Article
The temporal behaviour of the early optical emission from gamma-ray burst afterglows can be divided into four classes: fast-rising with an early peak, slow-rising with a late peak, flat plateaus and ...
rapid decays since first measurement. The fast-rising optical afterglows display correlations among peak flux, peak epoch and post-peak power-law decay index that can be explained with a structured outflow seen off-axis, but the shock origin (reverse or forward) of the optical emission cannot be determined. The afterglows with plateaus and slow rises may be accommodated by the same model, if observer location offsets are larger than for the fast-rising afterglows, or could be due to a long-lived injection of energy and/or ejecta in the blast wave. If better calibrated with more afterglows, the peak flux–peak epoch relation exhibited by the fast- and slow-rising optical light curves could provide a way to use this type of afterglows as standard candles.
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25.
Two‐stage approach for prediction of small‐for‐gestational‐age neonate and adverse perinatal outcome by routine ultrasound examination at 35–37 weeks' gestation
Akolekar, R.; Panaitescu, A. M.; Ciobanu, A. ...
Ultrasound in obstetrics & gynecology,
October 2019, 2019-Oct, 2019-10-00, 20191001, Volume:
54, Issue:
4
Journal Article
ABSTRACT
Background
Justification of prenatal screening for small‐for‐gestational‐age (SGA) fetuses near term is based on, first, evidence that such fetuses/neonates are at increased risk of ...
stillbirth and adverse perinatal outcome, and, second, the expectation that these risks can be reduced by medical interventions, such as early delivery. However, there are no randomized studies demonstrating that routine screening for SGA fetuses and appropriate interventions in the high‐risk group can reduce adverse perinatal outcome. Before such meaningful studies can be undertaken, it is essential that the best approach for effective identification of SGA neonates is determined, and that the contribution of SGA neonates to the overall rate of adverse perinatal outcome is established. In a previous study of pregnancies undergoing routine ultrasound examination at 35 + 0 to 36 + 6 weeks' gestation, we found that, first, screening by estimated fetal weight (EFW) < 10th percentile provided poor prediction of SGA neonates and, second, prediction of > 85% of SGA neonates requires use of EFW < 40th percentile.
Objectives
To examine the contribution of SGA fetuses to the overall rate of adverse perinatal outcome and, to propose a two‐stage approach for prediction of a SGA neonate at routine ultrasound examination at 35 + 0 to 36 + 6 weeks' gestation.
Methods
This was a prospective study of 45 847 singleton pregnancies undergoing routine ultrasound examination at 35 + 0 to 36 + 6 weeks' gestation. First, we examined the relationship between birth‐weight percentile and adverse perinatal outcome, defined as stillbirth, neonatal death or admission to the neonatal unit for ≥ 48 h. Second, we used a two‐stage approach for prediction of a SGA neonate and adverse perinatal outcome; in the first stage, fetal biometry was used to distinguish between pregnancies at very low risk (EFW ≥ 40th percentile) and those at increased risk (EFW < 40th percentile) and, in the second stage, the pregnancies with EFW < 40th percentile were stratified into high‐, intermediate‐ and low‐risk groups based on the results of EFW and pulsatility index in the uterine arteries, umbilical artery and fetal middle cerebral artery. Different percentiles of EFW and Doppler indices were used to define each risk category, and the performance of screening for a SGA neonate and adverse perinatal outcome in pregnancies delivered at ≤ 2, 2.1–4 and > 4 weeks after assessment was determined. We propose that the high‐risk group would require monitoring from initial assessment to delivery, the intermediate‐risk group would require monitoring from 2 weeks after initial assessment to delivery, the low‐risk group would require monitoring from 4 weeks after initial assessment to delivery, and the very low‐risk group would not require any further reassessment.
Results
First, although in neonates with low birth weight (< 10th percentile) the risk of adverse perinatal outcome is increased, 84% of adverse perinatal events occur in the group with birth weight ≥ 10th percentile. Second, in screening by EFW < 10th percentile, the predictive performance for a SGA neonate is modest for those born at ≤ 2 weeks after assessment (83% and 69% for neonates with birth weight < 3rd and < 10th percentiles, respectively), but poor for those born at 2.1–4 weeks (65% and 45%, respectively) and > 4 weeks (40% and 30%, respectively) after assessment. Third, improved performance of screening, especially for those delivered at > 2 weeks after assessment, is potentially achieved by a proposed new approach for stratifying pregnancies into management groups based on findings of EFW and Doppler indices (prediction of birth weight < 3rd and < 10th percentiles for deliveries at ≤ 2, 2.1–4 and > 4 weeks after assessment: 89% and 75%, 83% and 74%, and 88% and 82%, respectively). Fourth, the predictive performance for adverse perinatal outcome of EFW < 10th percentile is very poor (26%, 9% and 5% for deliveries at ≤ 2, 2.1–4 and > 4 weeks after assessment, respectively) and this is improved by the proposed new approach (31%, 22% and 29%, respectively).
Conclusions
This study presents an approach for stratifying pregnancies undergoing routine ultrasound examination at 35 + 0 to 36 + 6 weeks' gestation into four management groups based on findings of EFW and Doppler indices. This approach potentially has a higher predictive performance for a SGA neonate and adverse perinatal outcome than that of screening by EFW < 10th percentile. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.
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28.
Proposed clinical management of pregnancies after combined screening for pre‐eclampsia at 35–37 weeks' gestation
Panaitescu, A. M.; Wright, D.; Militello, A. ...
Ultrasound in obstetrics & gynecology,
September 2017, 2017-Sep, 2017-09-00, 20170901, Volume:
50, Issue:
3
Journal Article
ABSTRACT
Objective
To estimate the patient‐specific risk of pre‐eclampsia (PE) at 35–37 weeks' gestation by a combination of maternal characteristics and medical history with multiples of the median ...
(MoM) values of mean arterial pressure (MAP), uterine artery pulsatility index (UtA‐PI), serum placental growth factor (PlGF) and serum soluble fms‐like tyrosine kinase‐1 (sFlt‐1), and stratify women into high‐, intermediate‐ and low‐risk management groups.
Methods
This was a prospective observational study in women attending a third‐trimester ultrasound scan at 35–37 weeks as part of routine pregnancy care. Patient‐specific risks of delivery with PE at < 4 weeks from assessment and PE at < 42 weeks' gestation were calculated using the competing‐risks model to combine the prior risk from maternal characteristics and medical history with MoM values of MAP, UtA‐PI, PlGF and sFlt‐1. On the basis of these risks, the population was stratified into high‐, intermediate‐ and low‐risk groups. Different risk cut‐offs were used to vary the proportion of the population stratified into each risk category and the performance of screening for delivery with PE at < 40 and ≥ 40 weeks' gestation was estimated.
Results
The study population of 3703 singleton pregnancies included 38 (1.0%) with PE < 40 weeks' gestation and 22 (0.6%) with PE ≥ 40 weeks. Using a risk cut‐off of 1 in 50 for PE delivering at < 4 weeks after assessment to define the high‐risk group and a risk cut‐off of < 1 in 100 for PE delivering at < 42 weeks' gestation to define the low‐risk group, the proportion of the population stratified into high, intermediate and low risk was 12.7%, 28.8% and 58.5%, respectively. The high‐risk group contained 92% of pregnancies with PE at < 40 weeks' gestation and 73% of those with PE at ≥ 40 weeks. The intermediate‐risk group contained a further 27% of women with PE at ≥ 40 weeks. In the low‐risk group, none of the women developed PE at < 40 or ≥ 40 weeks' gestation.
Conclusion
The study presents risk stratification of PE by the combined test at 35–37 weeks, aiming to identify a high‐risk group in need of intensive monitoring from the time of the initial assessment and up to 40 weeks' gestation, an intermediate‐risk group in need of reassessment at 40 weeks' gestation and a low‐risk group that can be reassured that they are unlikely to develop PE. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.
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29.
Association of chronic hypertension with birth of small‐for‐gestational‐age neonate
Panaitescu, A. M.; Baschat, A. A.; Akolekar, R. ...
Ultrasound in obstetrics & gynecology,
September 2017, 2017-Sep, 2017-09-00, 20170901, Volume:
50, Issue:
3
Journal Article
ABSTRACT
Objective
To examine the effect of chronic hypertension (CH), with and without superimposed pre‐eclampsia (PE), on the incidence of a small‐for‐gestational‐age (SGA) neonate and to explore ...
the possible mechanism for such association.
Methods
Data for this study were derived from prospective screening for adverse pregnancy outcomes in women with singleton pregnancy attending their first routine hospital visit at 11–13 weeks' gestation, which included recording of maternal characteristics and medical history and measurement of mean arterial pressure (MAP). Birth‐weight Z‐score, adjusted for gestational age and maternal and pregnancy characteristics, and incidence of SGA were compared between those with and those without CH in the total population and in the subgroups of pregnancies with and without PE. Regression analysis was used to examine the relationship between MAP and birth‐weight Z‐score and incidence of SGA and PE in those with and those without CH.
Results
The study population constituted 74 226 pregnancies, including 1052 (1.4%) with CH and 73 174 without CH. PE developed in 233 (22.1%) cases of the group with CH and in 1662 (2.3%) of those without CH. In the group that developed PE, there was no significant difference for either median birth‐weight Z‐score or incidence of SGA between those with CH and those without CH. In the group without PE, the incidence of SGA was twice as high in those with CH than in those without. There was a significant association between log10 MAP multiples of the median and incidence of SGA and PE, which was more marked in those with CH than in those without.
Conclusion
CH is associated with an increased risk of SGA and PE and this is related to MAP at 11–13 weeks' gestation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.
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