Ultrasound estimation of birth weight in twin pregnancy: comparison of biometry algorithms in the STORK multiple pregnancy cohort

Longitudinal twin growth discordance patterns and adverse perinatal outcomes

BACKGROUND

Growth discordance in twin pregnancies is associated with increased perinatal morbidity and mortality, yet the patterns of discordance progression and the utility of Doppler assessments remain underinvestigated.

OBJECTIVE

The objective of this study was to conduct a longitudinal assessment of intertwin growth and Doppler discordance to identify possible distinct patterns and to investigate the predictive value of longitudinal discordance patterns for adverse perinatal outcomes in twin pregnancies.

STUDY DESIGN

This retrospective cohort study included twin pregnancies followed and delivered at a tertiary hospital in London (United Kingdom) between 2010 and 2023. We included pregnancies with at least 3 ultrasound assessments after 18 weeks and delivery beyond 34 weeks' gestation. Monoamniotic twin pregnancies, pregnancies with twin-to-twin transfusion syndrome, genetic or structural abnormalities, or incomplete data were excluded. Data on chorionicity, biometry, Doppler indices, maternal characteristics and obstetrics, and neonatal outcomes were extracted from electronic records. Doppler assessment included velocimetry of the umbilical artery, middle cerebral artery, and cerebroplacental ratio. Intertwin growth discordance was calculated for each scan. The primary outcome was a composite of perinatal mortality and neonatal morbidity. Statistical analysis involved multilevel mixed effects regression models and unsupervised machine learning algorithms, specifically k-means clustering, to identify distinct patterns of intertwin discordance and their predictive value. Predictive models were compared using the area under the receiver operating characteristic curve, calibration intercept, and slope, validated with repeated cross-validation. Analyses were performed using R, with significance set at P<.05.

RESULTS

Data from 823 twin pregnancies (647 dichorionic, 176 monochorionic) were analyzed. Five distinct patterns of intertwin growth discordance were identified using an unsupervised learning algorithm that clustered twin pairs based on the progression and patterns of discordance over gestation: low-stable (n=204, 24.8%), mild-decreasing (n=171, 20.8%), low-increasing (n=173, 21.0%), mild-increasing (n=189, 23.0%), and high-stable (n=86, 10.4%). In the high-stable cluster, the rates of perinatal morbidity (46.5%, 40/86) and mortality (9.3%, 8/86) were significantly higher compared to the low-stable (reference) cluster (P<.001). High-stable growth pattern was also associated with a significantly higher risk of composite adverse perinatal outcomes (odds ratio: 70.19, 95% confidence interval: 24.18-299.03, P<.001; adjusted odds ratio: 76.44, 95% confidence interval: 25.39-333.02, P<.001). The model integrating discordance pattern with cerebroplacental ratio discordance at the last ultrasound before delivery demonstrated superior predictive accuracy, evidenced by the highest area under the receiver operating characteristic curve of 0.802 (95% confidence interval: 0.712-0.892, P<.001), compared to only discordance patterns (area under the receiver operating characteristic curve: 0.785, 95% confidence interval: 0.697-0.873), intertwin weight discordance at the last ultrasound prior to delivery (area under the receiver operating characteristic curve: 0.677, 95% confidence interval: 0.545-0.809), combination of single measurements of estimated fetal weight and cardiopulmonary resuscitation discordance at the last ultrasound prior to delivery (area under the receiver operating characteristic curve: 0.702, 95% confidence interval: 0.586-0.818), and single measurement of cardiopulmonary resuscitation discordance only at the last ultrasound (area under the receiver operating characteristic curve: 0.633, 95% confidence interval: 0.515-0.751).

CONCLUSION

Using an unsupervised machine learning algorithm, we identified 5 distinct trajectories of intertwin fetal growth discordance. Consistent high discordance is associated with increased rates of adverse perinatal outcomes, with a dose-response relationship. Moreover, a predictive model integrating discordance trajectory and cardiopulmonary resuscitation discordance at the last visit demonstrated superior predictive accuracy for the prediction of composite adverse perinatal outcomes, compared to either of these measurements alone or a single value of estimated fetal weight discordance at the last ultrasound prior to delivery.

Validation of Fetal Medicine Foundation charts for fetal growth in twins: nationwide Danish cohort study

OBJECTIVE

To assess the validity of the Fetal Medicine Foundation (FMF) chorionicity-specific models for fetal growth in twin pregnancy.

METHODS

This was an external validation study of the FMF models using a nationwide Danish cohort of twin pregnancies. The cohort included all dichorionic (DC) and monochorionic diamniotic (MCDA) twin pregnancies with an estimated delivery date between 2008 and 2018, which satisfied the following inclusion criteria: two live fetuses at the first-trimester ultrasound scan (11-14 weeks' gestation); biometric measurements available for the calculation of estimated fetal weight (EFW) using the Hadlock-3 formula; and delivery of two liveborn infants. Validation involved assessing the distributional properties of the models and estimating the mean EFW Z-score deviations. Additionally, the models were applied to pregnancies that delivered preterm and attended non-scheduled visits (complicated pregnancies).

RESULTS

Overall, 8542 DC and 1675 MCDA twin pregnancies met the inclusion criteria. In DC twins, 17 084 fetuses were evaluated at a total of 95 346 ultrasound scans, of which 44.5% were performed at scheduled visits in pregnancies carried to 37 + 0 weeks or later. The median number of growth scans per DC twin fetus from 20 + 0 weeks onwards was four. The model showed good agreement with the validation cohort for scheduled visits in DC twins delivered at 37 + 0 weeks or later (mean ± SD EFW Z-score, -0.14 ± 1.05). In MCDA twins, 3350 fetuses underwent 31 632 eligible ultrasound scans, of which 59.5% were performed at scheduled visits in pregnancies carried to 36 + 0 weeks or later. The median number of growth scans per MCDA twin fetus from 16 + 0 weeks onwards was 10. The model showed favorable agreement with the validation cohort for scheduled visits in MCDA twins delivered at 36 + 0 weeks or later (mean ± SD EFW Z-score, -0.09 ± 1.01). Non-scheduled visits and preterm delivery before 37 + 0 weeks for DC twins and before 36 + 0 weeks for MCDA twins corresponded with smaller weight estimates, which was consistent with the study's definition of complicated pregnancy.

CONCLUSIONS

The FMF models provide a good fit for EFW measurements in our Danish national cohort of uncomplicated twin pregnancies assessed at routine scans. Therefore, the FMF models establish robust criteria for subsequent investigations and potential clinical applications. Future research should focus on exploring the consequences of clinical implementation, particularly regarding the identification of twins that are small-for-gestational age, as they are especially susceptible to adverse perinatal outcome. © 2024 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Association between fetal growth restriction and stillbirth in twin compared with singleton pregnancies

OBJECTIVES

Twin pregnancies are at higher risk of stillbirth compared to singletons. Fetal growth restriction (FGR) is a major cause of perinatal mortality, but its impact on twins vs singletons remains unclear. The primary objective of this study was to investigate the association of FGR and small-for-gestational age (SGA) with stillbirth in twin compared with singleton pregnancies. A secondary objective was to assess these associations stratified by gestational age at delivery. Furthermore, we aimed to compare the associations of FGR and SGA with stillbirth in twin pregnancies using twin-specific vs singleton birth-weight charts, stratified by chorionicity.

METHODS

This was a retrospective cross-sectional study of pregnancies receiving obstetric care and giving birth between 1999 and 2022 at St George's Hospital, London, UK. The exclusion criteria included triplet and higher-order pregnancies, those resulting in miscarriage or live birth at ≤ 23 + 6 weeks, termination of pregnancy and missing data regarding birth weight or gestational age at birth. Birth-weight data were collected and FGR and SGA were defined as birth weight <5th and <10th centiles, respectively. While standard logistic regression was used for singleton pregnancies, the association of FGR and SGA with stillbirth in twin pregnancies was investigated using mixed-effects logistic regression models. For twin pregnancies, intercepts were allowed to vary for twin pairs to account for intertwin dependency. Analyses were stratified by gestational age at delivery and chorionicity. Statistical significance was set at P ≤ 0.001.

RESULTS

The study included 95 342 singleton and 3576 twin pregnancies. There were 494 (0.52%) stillbirths in singleton and 41 (1.15%) stillbirths in twin pregnancies (17 dichorionic and 24 monochorionic). SGA and FGR were associated significantly with stillbirth in singleton pregnancies across all gestational ages at delivery: the odds ratios (ORs) for SGA and FGR were 2.36 ((95% CI, 1.78-3.13), P < 0.001) and 2.67 ((95% CI, 2.02-3.55), P < 0.001), respectively, for delivery before 32 weeks; 2.70 ((95% CI, 1.71-4.31), P < 0.001) and 2.82 ((95% CI, 1.78-4.47), P < 0.001), respectively, for delivery between 32 and 36 weeks; and 3.85 ((95% CI, 2.83-5.21), P < 0.001) and 4.43 ((95% CI, 3.16-6.12), P < 0.001), respectively, for delivery after 36 weeks. In twin pregnancies, when stratified by gestational age at delivery, both SGA and FGR determined by twin-specific birth-weight charts were associated with increased odds of stillbirth for those delivered before 32 weeks (SGA: OR, 3.87 (95% CI, 1.56-9.50), P = 0.003 and FGR: OR, 5.26 (95% CI, 2.11-13.01), P = 0.001), those delivered between 32 and 36 weeks (SGA: OR, 6.67 (95% CI, 2.11-20.41), P = 0.001 and FGR: OR, 9.54 (95% CI, 3.01-29.40), P < 0.001) and those delivered beyond 36 weeks (SGA: OR, 12.68 (95% CI, 2.47-58.15), P = 0.001 and FGR: OR, 23.84 (95% CI, 4.62-110.25), P < 0.001). However, the association of stillbirth with SGA and FGR in twin pregnancies was non-significant when diagnosis was based on singleton charts (before 32 weeks: SGA, P = 0.014 and FGR, P = 0.005; 32-36 weeks: SGA, P = 0.036 and FGR, P = 0.008; after 36 weeks: SGA, P = 0.080 and FGR, P = 0.063).

CONCLUSION

Our study demonstrates that SGA and, especially, FGR are associated significantly with an increased risk of stillbirth across all gestational ages in singleton pregnancies, and in twin pregnancies when twin-specific birth-weight charts are used. © 2024 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Hepatic arterial buffer response in monochorionic twins with selective fetal growth restriction

OBJECTIVES

Monochorionic twins (MC) have higher risk of perinatal morbi-mortality compared to singletons and dichorionic twins (DC). Selective fetal growth restriction (sFGR) increases the chances of adverse outcome. Hepatic arterial buffer response (HABR) is an important mechanism for maintaining liver perfusion. We hypothesised that HABR is active in monochorionic diamniotic twins (MCDA) with sFGR where restricted fetus may have liver hypoperfusion. The objective of this study is to test whether the HAV-ratio is diminished in pregnancies affected by selective fetal growth restriction pointing to activation of HABR in the growth-restricted fetus.

METHODS

sFGR was defined according to a consensus definition. Hepatic artery (HA) peak systolic velocity (PSV) was measured and its correlation with fetal Dopplers and pregnancy characteristics were determined. A ratio using HA-PSV (HAV-ratio) was calculated and its association with sFGR was established. Further analysis of HA-PSV was performed comparing z-scores between normal and growth restricted fetuses.

RESULTS

We included 202 MCDA pregnancies, 160 (79 %) normal and 42 (21 %) with sFGR. HAV-ratio was significant different between groups. The mean HAV-ratio was 1.01 (±0.20) for normal twins and 0.77 (±0.25) for sFGR. Furthermore, HA-PSV z-scores was significant increased in in growth-restricted fetus (0.94±1.45), while in normal fetuses was -0.16 (±0.97).

CONCLUSIONS

Our findings demonstrate that, in pregnancies with sFGR, HAV-ratio is significantly lower than in normal MCDA pregnancies. The lower HAV-ratio is due to an increase in HA PSV in the growth restricted fetus. This observation indicates an activation of HABR in the small fetus.

Investigation of the Association of Abdominal Circumference Discord-ance and Estimated Fetal Weight Discordance in Twins with Birth Weight Discordance

Background

Twin pregnancy is associated with a high risk of mortality and morbidity. It is necessary to estimate the weight difference of the fetuses with a reliable method to prevent possible complications. This study was conducted to compare the association between the Estimated fetal weight (EFW) discord-ance and the Abdominal Circumference (AC) discordance with birth weight in twins.

Methods

This was a descriptive-analytical and retrospective study. The statistical population was all twin pregnant mothers referred to Imam Khomeini Hospital in Ahvaz from 2017 to 2019. The sample size was determined with a census (540 people). Based on AC , the size of head circumference (HC), femur length (FL), and the Biparietal Diameter (BPD), EFW was calculated. Then the EFW Dis-cordance and AC Discordance were calculated and compared with the birth weight. Data were analyzed using SPSS18. Unpaired, Two-Tailed T-test and Pearson correlation test were used.

Results

The results showed that the mean discordance of fetal weight in twin pregnancies in the EFW method was 9.25%, in the AC method was 9.89% and finally, at birth, was 10.72%. The correla-tion of the weight difference between the two embryos in the AC method with the time of birth (r = 0.922 and P < 0.001) was higher than in the EFW method with the time of birth (r = 0.69 and P < 0.001) and finally, it was found that in detecting the discordance more than 20% and 25%, AC diagnostic power was good, but EFW was moderate.

Conclusion

Therefore, to evaluate the weight and weight difference in twin embryos, the AC method has the appropriate accuracy and compatibility. Another major prospective study to evaluate the diagnostic performance of AC and EFW mismatch based on gestational age at scan, incision point, and maternal and placental characteristics to determine true ultrasound diagnostic accuracy in predict-ing growth mismatch in twin pregnancy and optimal post-case management option is needed.

Hepatic arterial buffer response: activation in donor fetuses and the effect of laser ablation of intertwin anastomosis

OBJECTIVES

Hepatic arterial buffer response (HABR) is an important defence mechanism for maintaining liver blood flow. It is suspected that HABR is active in monochorionic diamniotic twins (MCDA) with twin-to-twin transfusion syndrome (TTTS) where donor compensates a setting of volume depletion and the recipient an overload. The present study investigates whether in TTTS, HABR is active in donor and/or recipient individually and try to determine if the activation of HABR is a direct response to TTTS.

METHODS

Hepatic artery (HA) peak systolic velocity (PSV) was measured in normal MCDA fetuses and TTTS. Correlation with relevant fetal Dopplers and characteristics were determined. Z-scores for HA-PSV (HAV-Z) were calculated and its association with TTTS in donors and recipients were determined as well as changes in HAV-Z after laser treatment.

RESULTS

In this study 118 MCDA were included, 61.9 % normal and 38.1 % TTTS. Of the TTTS 22 required laser treatment. A total of 382 scans were performed in normal group and 155 in TTTS. Our data demonstrates that in donors HAV-Z was 2.4 Z-scores higher compared to normal fetuses (β=2.429 95 % CI 1.887, 2.971; p<0.001) and after laser treatment HAV-Z reduced (β=-1.829 95 % CI -2.593, -1.064; p<0.001). There was no significant difference between recipients and normal (β=-0.092 95 % CI -0.633, 0.449; p=0.738).

CONCLUSIONS

HABR is active in TTTS, promoting an increased hepatic blood flow in donors. The activation is direct response to TTTS as shown by the reduction in HAV-Z after laser. This finding provides important insights into the pathophysiology of TTTS.

The Accuracy of Sonographically Estimated Fetal Weight and Prediction of Small for Gestational Age in Twin Pregnancy-Comparison of the First and Second Twins

Accurate sonographic estimation of fetal weight is essential for every pregnancy, especially in twin gestation. We conducted a retrospective analysis of the sonographically estimated fetal weight (sEFW) of all twin gestations performed within 14 days of delivery in a single center that aimed to evaluate the accuracy of sEFW in predicting neonatal weight and small for gestational age (SGA) by comparing the first fetus to the second. A total of 190 twin gestations were evaluated for the study. There was no statistically significant difference in the sEFW between the first and the second twins, but the second twin had a statistically significant lower birth weight (2434 vs. 2351 g, p = 0.028). No difference was found in median absolute systematic error (p = 0.450), random error, or sEFW evaluations that were within 10% of the birth weight between the fetuses (65.3% vs. 67.9%, p = 0.587). Reliability analysis demonstrated an excellent correlation between the sEFW and the birth weight for both twins; however, the Euclidean distance was slightly higher for the first twin (12.21%). For SGA prediction, overall, there was a low sensitivity and a high specificity for all fetuses, with almost no difference between the first and second twins. We found that sEFW overestimated the birth weight for the second twin, with almost no other difference in accuracy measures or SGA prediction.

Hepatic arterial buffer response in monochorionic diamniotic pregnancies with twin-to-twin transfusion syndrome

OBJECTIVES

Hepatic arterial buffer response (HABR) is an important regulatory process for hepatic blood flow. Its activity has been described in some fetal adverse conditions but in twin-to-twin transfusion syndrome (TTTS) it is unknown if such response is present. The aim of this study is to test the hypothesis that HABR operates in monochorionic diamniotic twins (MCDA) with TTTS.

METHODS

Hepatic artery pulsatility index (PI) and peak systolic velocity (PSV) were measured prospectively in 64 MCDA pregnancies. 43 without TTTS (group 1) and in 21 pregnancies with TTTS (group 2). We calculated ratios for PI (HAPI-ratio) and PSV (HAV-ratio) between recipient and donor in group 2 or bigger and smaller fetus in group 1 and compared groups. The association of HAV-ratio and HAPI ratio with TTTS, relation with other fetal Dopplers and reliability of measurement by a single operator were investigated.

RESULTS

HAV-ratio and HAPI-ratio appears to be independent from fetal Dopplers, estimated weight and gestational age. In group 2, HAV-ratio is lower than group 1 (p<0.001, 95% CI 0.443-0.643). In group 1 the mean HAV-ratio is 1.014 (±0.021) while in group 2 is 0.47 (±0.035). HAPI-ratio is lower in group 2 than in group 1 although this difference was not significant (p=0.066, 95% CI -0.007-0.231). A good reliability of measurements of hepatic artery PSV and PI was demonstrated by intraclass correlation coefficient analysis (ICC 0.971 95% CI 0.963-0.977, p<0.001 and ICC 0.694 95% CI 0.596-0.772, p<0.001, respectively).

CONCLUSIONS

Monochorionic pregnancies with TTTS are associated with lower HAV-ratios. This could be explained by an active HABR.

Timing of Delivery for Twins With Growth Discordance and Growth Restriction: An Individual Participant Data Meta-analysis

OBJECTIVE

First, to evaluate the risks of stillbirth and neonatal death by gestational age in twin pregnancies with different levels of growth discordance and in relation to small for gestational age (SGA), and on this basis to establish optimal gestational ages for delivery. Second, to compare these optimal gestational ages with previously established optimal delivery timing for twin pregnancies not complicated by fetal growth restriction, which, in a previous individual patient meta-analysis, was calculated at 37 0/7 weeks of gestation for dichorionic pregnancies and 36 0/7 weeks for monochorionic pregnancies.

DATA SOURCES

A search of MEDLINE, EMBASE, ClinicalTrials.gov, and Ovid between 2015 and 2018 was performed of cohort studies reporting risks of stillbirth and neonatal death in twin pregnancies from 32 to 41 weeks of gestation. Studies from a previous meta-analysis using a similar search strategy (from inception to 2015) were combined. Women with monoamniotic twin pregnancies were excluded.

METHODS OF STUDY SELECTION

Overall, of 57 eligible studies, 20 cohort studies that contributed original data reporting on 7,474 dichorionic and 2,281 monochorionic twin pairs.

TABULATION, INTEGRATION, AND RESULTS

We performed an individual participant data meta-analysis to calculate the risk of perinatal death (risk difference between prospective stillbirth and neonatal death) per gestational week. Analyses were stratified by chorionicity, levels of growth discordance, and presence of SGA in one or both twins. For both dichorionic and monochorionic twins, the absolute risks of stillbirth and neonatal death were higher when one or both twins were SGA and increased with greater levels of growth discordance. Regardless of level of growth discordance and birth weight, perinatal risk balanced between 36 0/7-6/7 and 37 0/7-6/7 weeks of gestation in both dichorionic and monochorionic twin pregnancies, with likely higher risk of stillbirth than neonatal death from 37 0/7-6/7 weeks onward.

CONCLUSION

Growth discordance or SGA is associated with higher absolute risks of stillbirth and neonatal death. However, balancing these two risks, we did not find evidence that the optimal timing of delivery is changed by the presence of growth disorders alone.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO, CRD42018090866.

Twin chorionicity-specific population birth-weight charts adjusted for estimated fetal weight

OBJECTIVES

To construct chorionicity-specific birth-weight reference charts for dichorionic diamniotic (DCDA) and monochorionic diamniotic (MCDA) twin pregnancies, incorporating estimated-fetal-weight (EFW) data in order to adjust for the relationship between suboptimal growth and preterm delivery. An additional aim was to determine if the inclusion of complicated twin pregnancies impacts on the reference charts produced.

METHODS

The inclusion criteria for this retrospective cohort study were twin pregnancy of known DCDA or MCDA chorionicity, known pregnancy outcome, last ultrasound scan within 14 days before birth and delivery between 25 and 38 weeks' gestation (Analysis A). An analysis was also conducted excluding pregnancies with complications recorded (Analysis B). Previously published twin EFW reference ranges were used in the analysis. A joint statistical model for EFW and observed birth weight for each pregnancy was created in order to estimate population birth-weight reference ranges corresponding to the distribution expected if all pregnancies delivered at any given gestational age. It was not assumed that the median EFW was equal to birth weight for any given gestational age. The models were fitted using a Bayesian approach.

RESULTS

We retrieved data on 1664 twin pregnancies, of which 707 DCDA and 241 MCDA pregnancies met the inclusion criteria. In Analysis A, the estimated population median birth weight was similar to the median EFW at around 27 weeks' gestation but fell below the EFW values with increasing gestation, being 156 g lower in both DCDA and MCDA pregnancies at 35 weeks; this finding was confirmed by direct comparison of the last EFW and birth-weight values in each pregnancy. When the analysis was repeated after excluding complicated twin pregnancies (Analysis B), compared with Analysis A, there was very little difference in the median birth-weight results obtained across gestation. The largest absolute difference between Analyses A and B for DCDA twins was at 31, 32 and 33 weeks, with a 9-g lower median birth weight in Analysis A compared with Analysis B. The largest absolute difference for MCDA twins was greater than that for DCDA twins, with a 21-g lower median birth weight at 25 weeks in Analysis A compared with Analysis B.

CONCLUSIONS

We have established population chorionicity-specific birth-weight reference charts for DCDA and MCDA twin pregnancies, corresponding to the range expected were all pregnancies to deliver at any given gestational age. In this population of twins, the median birth weight was consistently lower than that reported for singletons, and there was variation in the median birth weight at different gestational ages according to chorionicity. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology. - Legal Statement: This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

The accuracy of prenatal diagnosis of selective fetal growth restriction with second trimester Doppler ultrasound in monochorionic diamniotic twin pregnancies

BACKGROUND

Selective fetal restriction growth (sFGR) is one of the common diseases of monochorionic diamniotic (MCDA) twin pregnancies, resulting in many adverse outcomes. At present, second trimester ultrasonography is widely used in the prenatal diagnosis of sFGR, but the diagnostic effectiveness is still uncertain. The aim of this study is to assess the diagnostic accuracy of second trimester Doppler ultrasound measurements for sFGR.

METHODS

A retrospective study included 280 pregnant women (118 with and 162 without sFGR) with MCDA pregnancies was conducted in the fetal medicine center from Leiden University Medical Center from January 2008 to December 2013. The women participating had already undergone an ultrasound examination in the second trimester. The postnatal criteria of sFGR was a single birth weight (BW) < 3 rd percentile in a twin, or birth weight discordance (BWD)≥25% between two twins, while the BW of the smaller twin < 10th percentile. Early prenatal diagnosis of sFGR was defined as a single EFW < 3 rd percentile in a twin, or at least 2 of the following 4 parameters must be met (fetal weight of one fetus < 10th percentile, AC of one fetus <10th percentile, EFW discordance≥25%, UA pulsatility index (PI) of the smaller fetus > 95th percentile). According to the diagnosis of sFGR after birth, we evaluate diagnostic effectiveness of Doppler ultrasound in the second trimester for sFGR.

RESULTS

Of these 280 participants, the mean age was 32.06 ± 4.76 years. About 43.9% of pregnant women were primiparas. The ability of second trimester Doppler ultrasound to accurately diagnosed sFGR is 75.4%, missed diagnosis rate and the misdiagnosis rate were 24.6% and 10.5% respectively. The ROC curve indicated that the combination of AC discordance, EFW discordance, and small fetal UA blood flow was the best diagnostic indicator of sFGR in MCDA pregnancy with the AUC was 0.882 (95%CI, 0.839-0.926).

CONCLUSIONS

Second trimester Doppler and ultrasound measurements is an effective method for early prenatal diagnosis of sFGR. The combined indicator of AC discordance, EFW discordance, and the small fetal UA blood flow reaches highest diagnostic value.

Screening, Management and Delivery in Twin Pregnancy

The following AWMF guideline (DGGG/AGG & DEGUM responsible) deals with the diagnosis, screening and management of twins as well as the timing and mode of birth.Twin pregnancies can be classified as dichorionic diamniotic (DC DA), monochorionic diamniotic (MC DA) and monochorionic monoamniotic (MC MA) which are always monochorionic.Twin pregnancies can be concordant (both twins are affected) or discordant (only one twin is affected) for chromosomal defects, malformations, growth restriction and hemodynamic disorders.Chorionicity is the prognostically most significant parameter. Monochorial twins have significantly higher risks of intrauterine morbidity and mortality compared to dichorial twins.In particular, general aspects of twin pregnancies such as dating, determination of chorionicity and amnionicity, the labeling of twin fetuses and the perinatal switch phenomenon are discussed.Routine monitoring of MC and DC twin pregnancies with ultrasound at 11-13^+ 6 weeks of gestation for chromosomal defects, invasive prenatal diagnosis, first-trimester NT or CRL discrepancies, early diagnosis of fetal anatomical defects, and management of twins with abnormalities, including selective fetocide, is described.Second trimester screening and management for preterm birth, intrauterine selective growth restriction (sFGR), classification of monochorial twins with sFGR, and management of the surviving twin after the death of the co-twin are described.Complications exclusively affecting MC twins include Twin to Twin Transfusion Syndrome (TTTS) with the important topics screening, prognosis, complications of laser therapy, timing of delivery, risks for brain abnormalities and delayed neurological development, Twin Anemia-Polycythemia Sequence (TAPS) and Twin Reversed Arterial Perfusion (TRAP) Sequence. This also includes MC MA twins as well as conjoined twins.Finally, the birth mode and time for DC and MC twin pregnancies are described.The information is summarized in 62 recommendations for action, 4 tables and 8 illustrations with comprehensive background texts.The guideline is an international guideline adaptation (ISUOG, NICE) as well as a systematic literature search and is up-to-date.

Preventing term stillbirth: benefits and limitations of using fetal growth reference charts

PURPOSE OF REVIEW

This review examines the variation in clinical practice with regards to ultrasound estimation of fetal weight, as well as calculation of fetal weight centiles.

RECENT FINDINGS

Placental dysfunction is associated with fetal smallness from intrauterine malnutrition as well as fetal disability and even stillbirth from hypoxemia. Although estimating fetal weight can be done accurately, the issue of which fetal weight centile chart should be used continues to be a contentious topic. The arguments against local fetal growth charts based on national borders and customization for variables known to be associated with disease are substantial. As for other human diseases such as hypertension and diabetes, there is a rationale for the use of an international fetal growth reference standard. Irrespective of the choice of fetal growth reference standard, a significant limitation of small for gestational age (SGA) detection programs to prevent stillbirth is that the majority of stillborn infants at term were not SGA at the time of demise.

SUMMARY

Placental dysfunction can present with SGA from malnutrition and/or stillbirth from hypoxemia depending on the gestational age of onset. Emerging data show that at term, fetal Doppler arterial redistribution is associated more strongly with perinatal death than fetal size. Properly conducted trials of the role for maternal characteristics, fetal size, placental biomarkers, and Doppler assessing fetal well-being are required urgently.

Abdominal circumference discordance for prediction of small for gestational age at birth in twin pregnancies

OBJECTIVE

To evaluate whether single sonographic abdominal circumference (AC) discordancy estimation can predict small for gestational age (SGA) at birth in twin gestations.

METHODS

A retrospective analysis of prospectively collected data. Cohort included all twin gestations delivered at one university-affiliated medical center between 2010 and 2018, with available sonographic evaluation from 22 gestational weeks to term. Pregnancies complicated by fetal chromosomal abnormalities, major anomalies or twin to twin transfusion syndrome were excluded. One sonographic evaluation per pregnancy was selected randomly. AC discordance was calculated as (large twin AC - small twin AC)/large twin AC*100. Prediction of SGA at birth for at least one newborn (<10% percentile for gestational age by gender-specific local curves for multiples) was evaluated using ROC statistics with calculation of Youden index to establish best AC discordance cutoff. AC discordance prediction performance was compared to estimated fetal weight discordance performance. Results were adjusted for confounders using logistic regression analysis.

RESULTS

After exclusion, 236 twin gestations entered analysis. Of them, 200/236 (84.7%) were dichorionic-diamniotic twins. Mean gestational age at ultrasound evaluation and at delivery were 30.9 ± 4.4 and 35.9 ± 2.4 weeks, respectively. In 28/236 (11.8%) pregnancies, at least one neonate was born SGA. AC discordance predicted SGA at birth as good as sonographic estimated fetal weight (sEFW) discordance: ROC-AUC 0.76, 95% CI 0.67-0.85 vs. 0.77 95% CI 0.66-0.87, p < .001 for all. Best AC discordance cutoff for prediction of SGA at birth was 7.1% (57% sensitivity, 87% specificity), ROC-AUC 0.72 (95% CI 0.61-0.84, p < .001). Results remained significant after adjustment for maternal age, nulliparity, chorionicity and ultrasound to delivery interval (aOR 1.21 95% CI 1.1-1.32, p < .001).

CONCLUSION

According to our results, AC discordance at single sonographic evaluation can predict SGA at birth in twin gestations as good as sEFW discordance. Best cutoff for SGA prediction was 7.1%.

A cohort study of fetal growth in twin pregnancies by chorionicity: comparison with European and American standards

OBJECTIVE

To develop fetal growth standards for twin gestations by placental chorionicity in a Spanish population and compare them with European and American standards to estimate the suitability of their use in clinical practice.

STUDY DESIGN

This was a retrospective cohort study of 518 twin pregnancies, 435 dichorionic-diamniotic and 83 monochorionic-diamniotic, performed between January 2012 and December 2017. A total of 4,783 and 1,455 estimated fetal weights were considered from the 17^th to the 37^th week of gestation, using multilevel models, to build dichorionic-diamniotic and monochorionic-diamniotic standards, respectively. The percentages of small and large for gestational age were calculated as a model adjustment measure and adjustment to the studied data and the values provided by our model were compared against those of six European and American twin standards and three singleton standards. Correlation analyses between percentile predictions were performed using Cohen kappa coefficient. The predictive ability to detect small for gestational age was also provided by the sensitivity and positive predictive value.

RESULTS

We found slight differences between standards by chorionicity, being dichorionic-diamniotic percentiles slightly higher than monochorionic-diamniotic ones from the 17^th to 37^th weeks' gestation. For dichorionic-diamniotic cases, both our standard (9.8-8.2) and that of Grantz (8.2-10.5) showed good adjustments for the 10^th and 90^th percentiles while the other compared standards underestimated or overestimated them. For monochorionic-diamniotic cases, both our standard (10.2-8.5) and that of Shivkumar (11.4-6.8) had the most suitable adjustment. The correlation analysis between small and large for gestational age cases provided by standards, showed clear differences among them. Kappa's coefficient showed a substantial agreement between both Ananth (0.7) and Stirrup (0.69) dichorionic-diamniotic cases and our standard. There was also a substantial agreement between the Shivkumar (0.77) standard and our results for monochorionic-diamniotic cases. The correlation was moderate for all other comparisons.

CONCLUSIONS

Our model showed a good adjustment to the studied population. There are clear differences among small and large for gestational age cases provided by twin standards in our studied population. The twin growth standards depend on the population characteristics and model structure. We found the use of singleton standards for twin pregnancies inadequate.

Predictive value of prenatal ultrasound parameters for dichorionic growth discordant twins

BACKGROUND

Twin growth discordance was demonstrated to be a risk factor for adverse perinatal outcomes, and prenatal ultrasonographic methods were utilized to predict twin growth discordance to improve outcomes. The results currently reported are not consistent due to the poor unified parameters and gestational durations.

METHODS

A total of 71 dichorionic twins with growth discordance and 346 dichorionic twins with normal growth were respectively included in the retrospective cohort study. The weight discordance of more than 25% was defined as a "growth discordant twin". The clinical baseline information, maternal outcomes, twin birth weights and fetal growth parameters (which were measured by ultrasound) were compared between the two groups from early gestation to late gestation. Multiple logistic regression and receiver operating characteristic curves were adopted to evaluate the predictive value of the growth parameters.

RESULTS

Compared with normal dichorionic twins, the clinical baseline conditions were similar in the twins those finally developed growth discordance. The fetal growth parameters and the deepest volume pocket of amniotic fluid in early and mid-pregnancy showed no obvious predictive values. The fetal growth parameters in late pregnancy showed predictive values, especially the discordance of estimated fetal weight (EFW) in the early third-trimester (P < 0.001, area under the curve, 0.822; the cut-off value, 20%; sensitivity, 66.67%; specificity, 91.30%; positive predictive value, 88.46%).

CONCLUSION

Two assessment approaches were suggested and adopted to predict twin growth discordance in the current study. Twin growth should be assessed longitudinally and dynamically. Normal twins may show growth imbalance in the early stage. The discordance of EFW in late pregnancy may be a useful indicator for a growth discordance of more than 25%, which is required further confirmation.

Stillbirth at term: Does size really matter?

Placental dysfunction has a deleterious influence on fetal size and is associated with higher rates of perinatal morbidity and mortality. This association underpins the strategy of fetal size evaluation as a mechanism to identify placental dysfunction and prevent stillbirth. The optimal method of routine detection of small for gestational age (SGA) remains to be clarified with choices between estimation of symphyseal-fundal height versus routine third-trimester ultrasound, various formulae for fetal weight estimation by ultrasound, and the variable use of national, customized, or international fetal growth references. In addition to these controversies, the strategy for detecting SGA is further undermined by data demonstrating that the relationship between fetal size and adverse outcome weakens significantly with advancing gestation such that near term, the majority of stillbirths and adverse perinatal outcomes occur in normally sized fetuses. The use of maternal serum biochemical and Doppler parameters near term appears to be superior to fetal size in the identification of fetuses compromised by placental dysfunction and at increased risk of damage or demise. Multiparameter models and predictive algorithms using maternal risk factors, and biochemical and Doppler parameters have been developed, but need to be prospectively validated to demonstrate their effectiveness.

New reference values for biometrical measurements and sonographic estimated fetal weight in twin gestations and comparison to previous normograms

Objective To construct new reference values for biometrical measurements and sonographic estimated fetal weight (sEFW) in twin gestations and compare them to previously published normograms. Methods A retrospective analysis of sEFW evaluations of twin gestations was performed between 2011 and 2016 in a single university-affiliated medical center. sEFW was calculated using the Hadlock 1985 formula. To avoid selection bias, one evaluation per pregnancy was randomly selected. Following mathematical transformation to obtain normality of values, normograms were constructed using a best-fit regression model for estimation of mean and standard deviation at each gestational age (GA). Normograms were validated by applying all observations to ensure equal distribution at parallel percentiles. Our normograms were then compared to previously published sEFW normograms for twin gestations. Results A total of 864 sEFW evaluations were performed on 195 twin pregnancies at 22-39 gestational weeks. Of them, 390 entered the primary analysis. The rest were left for validation. Seventy percent of the cohort were dichorionic-diamniotic twins (136/195), 16% (32/195) were monochorionic-diamniotic twins and three (1.5%) were monochorionic-monoamniotic twins. Twenty-four fetuses lacked data on chorionicity. The rest were monochorionic twins or were of unknown chorionicity. Values corresponding to the 2.5th, 10th, 50th, 90th and 97.5th percentiles for sEFW are presented for every GA. Validation by applying all 864 evaluations on constructed normograms was achieved. Comparison to previously published twins' sEFW normograms demonstrated wide variation between curves. Conclusion New reference values for biometrical measurements and sEFW in twin gestations are presented for clinical and research use. Comparison to other curves demonstrates the wide variability and need for further investigation on twin's normal growth.

The use of magnetic resonance imaging in the prediction of birthweight

Extremes of fetal growth can increase adverse pregnancy outcomes, and this is equally applicable to single and multiple gestations. Traditionally, these cases have been identified using simple two-dimensional ultrasound which is quite limited by its low precision. Magnetic resonance imaging (MRI) has now been used for many years in obstetrics, mainly as an adjunct to ultrasound for congenital abnormalities and increasingly as part of the post-mortem examination. However, MRI can also be used to accurately assess fetal weight as first demonstrated by Baker et al in 1994, using body volumes rather than standard biometric measurements. This publication was followed by several others, all of which confirmed the superiority of MRI; however, despite this initial promise, the technique has never been successfully integrated into clinical practice. In this review, we provide an overview of the literature, detail the various techniques and formulas currently available, discuss the applicability to specific high-risk groups and present our vision for the future of MRI within clinical obstetrics.

Magnetic resonance imaging for prenatal estimation of birthweight in pregnancy: review of available data, techniques, and future perspectives

Fetuses at the extremes of growth abnormalities carry a risk of perinatal morbidity and death. Their identification traditionally is done by 2-dimensional ultrasound imaging, the performance of which is not always optimal. Magnetic resonance imaging superbly depicts fetal anatomy and anomalies and has contributed largely to the evaluation of high-risk pregnancies. In 1994, magnetic resonance imaging was introduced for the estimation of fetal weight, which is done by measuring the fetal body volume and converting it through a formula to fetal weight. Approximately 10 studies have shown that magnetic resonance imaging is more accurate than 2-dimensional ultrasound imaging in the estimation of fetal weight. Yet, despite its promise, the magnetic resonance imaging technique currently is not implemented clinically. Over the last 5 years, this technique has evolved quite rapidly. Here, we review the literature data, provide details of the various measurement techniques and formulas, consider the application of the magnetic resonance imaging technique in specific populations such as patients with diabetes mellitus and twin pregnancies, and conclude with what we believe could be the future perspectives and clinical application of this challenging technique. The estimation of fetal weight by ultrasound imaging is based mainly on an algorithm that takes into account the measurement of biparietal diameter, head circumference, abdominal circumference, and femur length. The estimation of fetal weight by magnetic resonance imaging is based on one of the 2 formulas: (1) magnetic resonance imaging-the estimation of fetal weight (in kilograms)=1.031×fetal body volume (in liters)+0.12 or (2) magnetic resonance imaging-the estimation of fetal weight (in grams)=1.2083×fetal body volume (in milliliters)ˆ0.9815. Comparison of these 2 formulas for the detection of large-for-gestational age neonates showed similar performance for preterm (P=.479) and for term fetuses (P=1.000). Literature data show that the estimation of fetal weight with magnetic resonance imaging carries a mean or median relative error of 2.6 up to 3.7% when measurements were performed at <1 week from delivery; whereas for the same fetuses, the relative error at 2-dimensional ultrasound imaging varied between 6.3% and 11.4%. Further, in a series of 270 fetuses who were evaluated within 48 hours from birth and for a fixed false-positive rate of 10%, magnetic resonance imaging detected 98% of large-for-gestational age neonates (≥95th percentile for gestation) compared with 67% with ultrasound imaging estimates. For the same series, magnetic resonance imaging applied to the detection of small-for-gestational age neonates ≤10th percentile for gestation, for a fixed 10% false-positive rate, reached a detection rate of 100%, compared with only 78% for ultrasound imaging. Planimetric measurement has been 1 of the main limitations of magnetic resonance imaging for the estimation of fetal weight. Software programs that allow semiautomatic segmentation of the fetus are available from imaging manufacturers or are self-developed. We have shown that all of them perform equally well for the prediction of large-for-gestational age neonates, with the advantage of the semiautomatic methods being less time-consuming. Although many challenges remain for this technique to be generalized, a 2-step strategy after the selection of a group who are at high risk of the extremes of growth abnormalities is the most likely scenario. Results of ongoing studies are awaited (ClinicalTrials.gov Identifier # NCT02713568).

Prediction of birth weight in twin pregnancies using fractional limb volumes by three-dimensional ultrasonography

Objective: To predict birth weight using fetal fractional limb volumes (FLVs) by three-dimensional (3D) ultrasonography in twin pregnancies.Method: This prospective observational cohort study evaluated 51 twin pregnancies, including 28 dichorionic and 23 monochorionic pregnancies. Ultrasound examinations were performed up to 5 d before delivery. Birth weight prediction models were developed using the fractional arm volume (FAV), fractional thigh volume (FTV), and Hadlock's formula and were compared with the actual birth weight.Results: The mean gestational age at the time of ultrasound examination was 35.3 weeks. The mean birth weight was slightly higher in dichorionic than in monochorionic pregnancies 2391.2 versus 2352.4 g. The measurements using FTV were the closest to actual birth weights. For the total group, the Hadlock formula had mean percentage change of 7.18% while the FTV model presented mean percentage change of 6.62% in relation to birth weight. However, no significant difference was noted between Hadlock's formula and FTV p = .363 and .678 for dichorionic and monochorionic pregnancies, respectively.Conclusions: FTV accurately predicted birth weight in twin monochorionic and dichorionic pregnancies. However, Hadlock's formula should still be used.

The value of ultrasound in predicting isolated inter-twin discordance and adverse perinatal outcomes

PURPOSE

To investigate the value of ultrasound approaching delivery to predict isolated inter-twin discordance and adverse perinatal outcomes.

METHODS

We retrospectively included twin pregnancies with sonography approaching delivery in ten maternal-foetal medicine centres in China from 2013 to 2014. Estimated foetal weight (EFW) and inter-twin EFW disparity (EFWD) were calculated based on biometry parameters. Percentage errors between EFW and actual birthweight or between EFWD and actual inter-twin disparity were calculated. ROC curves and multiple logistic regression were applied to evaluate the ability of EFWD to predict inter-twin disparity ≥ 25%, stillbirth, asphyxia and admission to a neonatal intensive unit (NICU). Chorionicity-stratified analysis was further performed.

RESULTS

Two hundred sixty-six monochorionic and 760 dichorionic twin pregnancies were analysed. The percentage errors in foetal weight estimations were 7-13%, whereas percentage errors in the estimation of inter-twin disparity were nearly 100%. Among eight formulas, Hadlock1 performed best, with a detectable rate of 65% and a false positive rate of 5% when predicting inter-twin disparity ≥ 25%. EFWD ≥ 22% was strongly associated with stillbirth (OR = 4.17, 95% CI 1.40-12.40) and NICU admission (OR = 3.48, 95% CI 2.03-5.97) after adjustment for gestational age, parity and abnormal umbilical systolic/diastolic ratio. Ultrasound had better predictive ability in monochorionic twins.

CONCLUSION

The predictive value of ultrasound for isolated inter-twin discordance and adverse perinatal outcomes was limited, which was possibly due to the magnifying of systematic errors in the disparity estimation compared with weight estimation. Despite this, abnormal biometry was an independent contributor for the poor prognosis of neonates.

Ultrasound surveillance in twin pregnancy: An update for practitioners

Ultrasound has revolutionised the management of multiple pregnancies and their complications. Increasing frequency of twin pregnancies mandates familiarity of all clinicians with the relevant pathologies and evidence-based surveillance and management protocols for their care. In this review, we summarise the latest evidence relating to ultrasound surveillance of twin pregnancies including first trimester assessment and screening, growth surveillance and the detection and management of the complications of monochorionic pregnancies including twin-to-twin-transfusion syndrome, selective fetal growth restriction, twin reversed arterial perfusion sequence and conjoined twinning.

The role of ultrasound in the prediction of birth weight discordance in twin pregnancies: are we there yet?

OBJECTIVE

To analyze the accuracy of ultrasound prediction of birth weight discordance (BWD) and the influence of chorionicity and fetal growth restriction (FGR) on ultrasound performance.

METHODS

Retrospective analysis of 176 twin pregnancies at a Portuguese tertiary center, between 2008 and 2014. Last ultrasound biometry was recorded. Cases with delivery before 24 weeks, fetal malformations, interval between last ultrasound and deliver >3 weeks, twin-to-twin transfusion syndrome and monoamniotic pregnancies were excluded. The accuracy of prediction of BWD was assessed using the area under the receiver-operating characteristics curve (AUC).

RESULTS

BWD ≥20% was present in 21.6% of twin pregnancies. EBW had the best predictive performance for BWD (AUC 0.838, 95%CI 0.760-0.916), with a negative predictive value of 86.9% and a positive predictive value of 51.3%. Chorionicity did not influence ultrasound performance. None of the biometric variables analyzed was predictive of BWD in pregnancies without FGR.

CONCLUSION

The accuracy of ultrasound in the prediction of BWD is limited, particularly in pregnancies without fetal growth restriction. Clinical decisions should not rely on BWD alone.

The accuracy of ultrasound estimation of fetal weight in comparison to birth weight: A systematic review

Ultrasound estimation of fetal weight is a highly influential factor in antenatal management, guiding both the timing and mode of delivery of a pregnancy. Although substantial research has investigated the most accurate ultrasound formula for calculating estimated fetal weight, current evidence indicates significant error levels. The aim of this systematic review was to identify the most accurate method, whilst identifying sources of inaccuracy in order to facilitate recommendations for future practice. Seven studies met the inclusion criteria and 11 different formulae were assessed; ultrasound calculation of fetal weight was most commonly overestimated. The Hadlock A formula produced the most accurate results, with the lowest levels of random error. Methods incorporating just two measurement parameters were inconsistent, producing large random errors across multiple studies. Key sources of inaccuracy included difficulties obtaining accurate fetal measurements in late gestation; the remainder were operator dependent, including lack of experience and insufficient training and audit. The accuracy of ultrasound estimated fetal weight has improved in the last decade, though a lack of consistency remains evident. National implementation of a rigorous audit programme would likely improve accuracy further, and increase the confidence and clinical value of the method.

Comparison of conventional 2D ultrasound to magnetic resonance imaging for prenatal estimation of birthweight in twin pregnancy

BACKGROUND

During prenatal follow-up of twin pregnancies, accurate identification of birthweight and birthweight discordance is important to identify the high-risk group and plan perinatal care. Unfortunately, prenatal evaluation of birthweight discordance by 2-dimensional ultrasound has been far from optimal.

OBJECTIVE

The objective of the study was to prospectively compare estimates of fetal weight based on 2-dimensional ultrasound (ultrasound-estimated fetal weight) and magnetic resonance imaging (magnetic resonance-estimated fetal weight) with actual birthweight in women carrying twin pregnancies.

STUDY DESIGN

Written informed consent was obtained for this ethics committee-approved study. Between September 2011 and December 2015 and within 48 hours before delivery, ultrasound-estimated fetal weight and magnetic resonance-estimated fetal weight were conducted in 66 fetuses deriving from twin pregnancies at 34.3-39.0 weeks; gestation. Magnetic resonance-estimated fetal weight derived from manual measurement of fetal body volume. Comparison of magnetic resonance-estimated fetal weight and ultrasound-estimated fetal weight measurements vs birthweight was performed by calculating parameters as described by Bland and Altman. Receiver-operating characteristic curves were constructed for the prediction of small-for-gestational-age neonates using magnetic resonance-estimated fetal weight and ultrasound-estimated fetal weight. For twins 1 and 2 separately, the relative error or percentage error was calculated as follows: (birthweight - ultrasound-estimated fetal weight (or magnetic resonance-estimated fetal weight)/birthweight) × 100 (percentage). Furthermore, ultrasound-estimated fetal weight, magnetic resonance-estimated fetal weight, and birthweight discordance were calculated as 100 × (larger estimated fetal weight-smaller estimated fetal weight)/larger estimated fetal weight. The ultrasound-estimated fetal weight discordance and the birthweight discordance were correlated using linear regression analysis and Pearson's correlation coefficient. The same was done between the magnetic resonance-estimated fetal weight and birthweight discordance. To compare data, the χ², McNemar test, Student t test, and Wilcoxon signed rank test were used as appropriate. We used the Fisher r-to-z transformation to compare correlation coefficients.

RESULTS

The bias and the 95% limits of agreement of ultrasound-estimated fetal weight are 2.99 (-19.17% to 25.15%) and magnetic resonance-estimated fetal weight 0.63 (-9.41% to 10.67%). Limits of agreement were better between magnetic resonance-estimated fetal weight and actual birthweight as compared with the ultrasound-estimated fetal weight. Of the 66 newborns, 27 (40.9%) were of weight of the 10th centile or less and 21 (31.8%) of the fifth centile or less. The area under the receiver-operating characteristic curve for prediction of birthweight the 10th centile or less by prenatal ultrasound was 0.895 (P < .001; SE, 0.049), and by magnetic resonance imaging it was 0.946 (P < .001; SE, 0.024). Pairwise comparison of receiver-operating characteristic curves showed a significant difference between the areas under the receiver-operating characteristic curves (difference, 0.087, P = .049; SE, 0.044). The relative error for ultrasound-estimated fetal weight was 6.8% and by magnetic resonance-estimated fetal weight, 3.2% (P < .001). When using ultrasound-estimated fetal weight, 37.9% of fetuses (25 of 66) were estimated outside the range of ±10% of the actual birthweight, whereas this dropped to 6.1% (4 of 66) with magnetic resonance-estimated fetal weight (P < .001). The ultrasound-estimated fetal weight discordance and the birthweight discordance correlated significantly following the linear equation: ultrasound-estimated fetal weight discordance = 0.03 + 0.91 × birthweight (r = 0.75; P < .001); however, the correlation was better with magnetic resonance imaging: magnetic resonance-estimated fetal weight discordance = 0.02 + 0.81 × birthweight (r = 0.87; P < .001).

CONCLUSION

In twin pregnancies, magnetic resonance-estimated fetal weight performed immediately prior to delivery is more accurate and predicts small-for-gestational-age neonates significantly better than ultrasound-estimated fetal weight. Prediction of birthweight discordance is better with magnetic resonance imaging as compared with ultrasound.

Diagnostic accuracy of ultrasound in predicting birth-weight discordance in twin pregnancy: systematic review and meta-analysis

OBJECTIVE

To investigate the diagnostic performance of ultrasound in predicting birth-weight (BW) discordance in twin pregnancy.

METHODS

Electronic databases PubMed, EMBASE and CINAHL were searched using combinations of MeSH terms 'birth weight', 'discordance', 'twins' and 'ultrasound'. Summary estimates of sensitivity, specificity, positive and negative likelihood ratios and diagnostic odds ratios for the predictive accuracy of sonographically estimated fetal-weight (EFW) discordance and abdominal-circumference (AC) discordance in predicting BW discordance were computed using hierarchical summary receiver-operating characteristics curves.

RESULTS

Twenty studies (including 5826 twin pregnancies) were included. EFW discordance ≥ 20% had a sensitivity of 65.4% and specificity of 90.8% in predicting BW discordance ≥ 20%. The predictive performance of ultrasound performed within 1 month, 2 weeks and 3 days before birth was 61.4%, 72.3% and 78.9%, respectively. EFW discordance ≥ 25% had a sensitivity of 57.7% and specificity of 95.2% in predicting BW discordance ≥ 25%. The sensitivity of EFW discordance ≥ 25% detected within 1 month, 2 weeks and 3 days before birth was 60.0%, 75.0% and 60.3%, respectively, while the corresponding values for specificity were 97.7%, 96.2% and 87.3%, respectively. In view of the different cut-offs reported among studies, it was not possible to perform comprehensive data synthesis for each AC discordance cut-off. The optimal diagnostic performance of AC discordance was for prediction of BW discordance ≥ 25%, with a sensitivity of 70.8% and specificity of 86.4%.

CONCLUSION

Ultrasound EFW discordance has an overall moderate accuracy in predicting BW discordance in twin pregnancy. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

A new mathematical formula to predict the foetal weight in twin pregnancies: A comparison of it with 19 different formulas

One hundred and seventy-two twin-pregnant patients were enrolled. The estimated foetal weight was calculated using 19 different formulas. Ong's formula (0.954 (95%CI = 0.938/0.966)), which was designed specifically for twins, produced the highest Cronbach's alpha value followed by Hadlock II (0.952 (95%CI = 0.935/0.965)), Hadlock I (0.952 (95%CI = 0.935/0.964)), Hadlock III (0.952 (95%CI = 0.935/0.964)), Hadlock IV (0.952 (95%CI = 0.935/0.964)) and our formula (0.952 (95%CI = 0.935/0.964)), which produced the same Cronbach's alpha values for twin A. For twin B, our formula produced the highest Cronbach's alpha value (0.961 (95%CI = 0.948/0.972) followed by Hadlock II (0.960 (95%CI = 0.946/0.971)), Hadlock I (0.960 (95%CI = 0.946/0.970)), Hadlock III (0.960 (95%CI = 0.946/0.970)) and Hadlock IV (0.960 (95%CI = 0.946/0.970)). In conclusion, our formula (AC, FL) performed well in predicting the foetal weights in twin pregnancies (>24 weeks) in our study. However, it should be tested in other populations. Hadlock II (AC, FL) produced a comparable performance to Hadlock I (BPD, HC, AC, FL), Hadlock III (BPD, AC, FL) and Hadlock IV (HC, AC, FL). Hadlock II may be preferable in twin pregnancies since it is based on AC and FL only.

Sonographic fetal weight estimation in normal and overweight/obese healthy term pregnant women by gestation-adjusted projection (GAP) method

PURPOSE

The objective of this study is to assess the ultrasound accuracy in fetal weight estimation related to the time distance between the actual weight recorded at delivery and the period of sonography among normal and overweight/obese pregnant women within 3 weeks prior birth at term.

METHODS

Four-hundred and ninety patients with healthy pregnancy were studied in a cohort study. The absolute percent error in estimation was achieved by gestation-adjusted projection method from Hadlock model for weight calculation as measure of accuracy. The mean percentage error variation over the weeks was correlated to maternal body mass index (BMI, Kg/m(2)) at ultrasound. The relationship between BMI and ultrasound performance was assessed by linear regression.

RESULTS

The overall proportion of supposed sonographic estimated fetal weight at birth within ±10 % of the birth weight significantly declines over the weeks (P = .016). The trend toward a progressive deterioration in ultrasound accuracy is not statistically significant for normal weight women (P = .272) but it is for over-weight/obese (P = .044). On univariate analysis, the absolute percent error and absolute error are positively related to BMI.

CONCLUSIONS

Accuracy is related to the week at ultrasound scan with a gradual deterioration over the time and it worsens with increasing distance in days between the date of ultrasounds and delivery. The deterioration is greater for BMI ≥ 25.

Discordance in fetal biometry and Doppler are independent predictors of the risk of perinatal loss in twin pregnancies

OBJECTIVE

Impaired fetal growth might be better evaluated in twin pregnancies by assessing the intertwin discordance rather than the individual fetal size. The aim of this study was to investigate the prediction of perinatal loss in twin pregnancy using discordance in fetal biometry and Doppler.

STUDY DESIGN

This was a retrospective cohort study in a tertiary referral center. The estimated fetal weight (EFW), umbilical artery (UA) pulsatility index (PI), middle cerebral artery (MCA) PI, cerebroplacental ratio (CPR), and their discordance recorded at the last ultrasound assessment before delivery or demise of one or both fetuses were converted into centiles or multiples of the median (MoM). The discordance was calculated as the larger value-smaller value/larger value. A logistic regression analysis was performed to identify, and adjust for, potential confounders. The predictive accuracy was assessed using receiver-operating characteristic curve analysis.

RESULTS

The analysis included 620 (464 dichorionic diamniotic and 156 monochorionic diamniotic) twin pregnancies (1240 fetuses). Perinatal loss of one or both fetuses complicated 16 pregnancies (2.6%). The combination of EFW discordance and CPR discordance had the best predictive performance (area under the curve, 0.96; 95% confidence interval, 0.92-1.00) for perinatal mortality. The detection rate, false-positive rate, positive likelihood ratio, and negative likelihood ratio were 87.5%, 6.7%, 13.08, and 0.13, respectively. The EFW centile, EFW below the 10th centile (small for gestational age), UA PI discordance, MCA PI discordance, and MCA PI MoM were significantly associated with the risk of perinatal loss on univariate analysis, but these associations became nonsignificant after adjusting for other confounders (P = .097, P = .090, P = .687, P = .360, and P = .074, respectively). The UA PI MoM, CPR MoM, EFW discordance, and CPR discordance were all independent predictors of the risk of perinatal loss, even after adjusting for potential confounders (P = .022, P = .002, P < .001, and P = .010, respectively).

CONCLUSION

EFW discordance and CPR discordance are independent predictors of the risk of perinatal loss in twin pregnancies. Their combination could identify the majority of twin pregnancies at risk of perinatal loss. These findings highlight the importance of discordance in Doppler indices of fetal hypoxia, as well as fetal size, in assessing the risk of perinatal mortality.

An ultrasound-based fetal weight reference for twins

OBJECTIVE

The objective of the study was to construct an ultrasound-based estimated fetal weight-for-gestational-age reference for twin fetuses, stratified by chorionicity.

STUDY DESIGN

We performed a retrospective cohort study of live-born nonanomalous twins delivered longer than 34 weeks at the Royal Victoria Hospital (Montreal, Canada). Fetal weight was estimated using ultrasound biometric measurements combined using Hadlock's formula. Multilevel linear regression models were used to adjust for clustering by twin pregnancy and to account for the serial ultrasound measurements taken on each fetus. Based on this model, smoothed estimates of fetal weight were made for the third, 10th, 50th, 90th, and 97th percentiles of the fetal weight distribution. Fetal weight references were stratified by fetal chorionicity.

RESULTS

A total of 642 twin fetuses with a total of 3078 ultrasound observations were included. Sixteen percent of the cohort was monochorionic. Fetal growth accelerated in the second trimester and continued in a linear pattern in the third trimester until term. As expected, the median weight for monochorionic twins was lighter than the median weight for dichorionic twins throughout pregnancy.

CONCLUSION

The reference values created in this study address serious methodological limitations of existing reference charts and thus provide an improved tool for assessing fetal growth in twin pregnancies. Importantly, dichorionic twins deviated from singleton reference charts at approximately 32 weeks, whereas monochorionic twins deviated at 28 weeks.

Fetal growth reference ranges in twin pregnancy: analysis of the Southwest Thames Obstetric Research Collaborative (STORK) multiple pregnancy cohort

OBJECTIVE

To generate reference charts for expected fetal growth in dichorionic diamniotic (DCDA) and monochorionic diamniotic (MCDA) twin pregnancies and to compare these with those from singleton pregnancies.

METHODS

This was a retrospective study of biometric measurements from serial ultrasound examinations of twin pregnancies in the second and third trimesters, from 14 weeks' gestation to term, collected by nine hospitals over a 10-year period. The measurements obtained in each fetus at each examination included head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL). Multilevel mixed effects statistical models were used to evaluate growth in each biometric variable in relation to gestational age, taking account of the serial examinations and the association between the two fetuses in each pregnancy, with separate models constructed for DCDA and MCDA pregnancies.

RESULTS

The final dataset for analysis included a total of 9866 second- and third-trimester ultrasound examinations in 1802 DCDA and 323 MCDA twin pregnancies, with a median of five (range, 1-14) scans per pregnancy. For each variable, the mean value for DCDA twins was close to the reported value in singletons at 20-30 weeks and showed a decrease relative to singletons beyond 30 weeks. The differences were greater for AC and HC, for which the mean in twins was approximately equivalent to the 30th percentile in singletons at 18 weeks, the 35th percentile at 25 weeks and the 30th percentile at 35 weeks. Fetuses in MCDA twin pregnancies displayed lower mean measurements than did those in DCDA pregnancies throughout the gestational age range considered.

CONCLUSIONS

Ultrasound biometry shows a small but statistically significant reduction in fetal growth in twin pregnancies relative to that in singletons, particularly in the third trimester, with a more marked difference for MCDA than for DCDA pregnancies.