Positive predictive value of suspected growth aberration in twin gestations

Incidence of small-for-gestational-age infant birthweight following early intertwin fetal growth discordance in dichorionic and monochorionic twin pregnancies

BACKGROUND

Serial growth scans are routinely recommended for twin pregnancies to identify fetal growth restriction (defined as an estimated fetal weight of <10th percentile), which can result in increased perinatal morbidity and mortality. However, the clinical significance of early intertwin growth discordance in the absence of fetal growth restriction remains unclear.

OBJECTIVE

This study aimed to compare the rates of small-for-gestational-age infants among twin pregnancies with intertwin growth discordance in the absence of fetal growth restriction with that among twin pregnancies with concordant, normal growth identified by ultrasound between 24 0/7 and 31 6/7 weeks' gestation.

STUDY DESIGN

This was a retrospective cohort study of twin deliveries at a single hospital from 2010 to 2019. Pregnancies without fetal growth restriction were categorized as discordant or concordant using the earliest prenatal growth ultrasound between 24 0/7 and 31 6/7 weeks' gestation. Discordance was defined as an estimated fetal weight difference of ≥18% between twins. Pregnancies with major fetal anomalies, no growth ultrasound between 24 0/7 and 31 6/7 weeks' gestation, or twin-twin transfusion syndrome were excluded. The cohort was stratified by chorionicity. Our primary outcome was small-for-gestational-age defined as <10th percentile per the Fenton growth curve at delivery. Secondary outcomes included gestational age at delivery, mode of delivery, neonatal intensive care unit admission, length of stay, and neonatal complications and placental pathology.

RESULTS

Of the 707 twin pregnancies that met the inclusion criteria, 558 (79%) were dichorionic and 149 (21%) were monochorionic. Most pregnancies were concordant on ultrasound between 24 0/7 and 31 6/7 weeks' gestation (dichorionic, 93%; monochorionic, 87%). Regardless of chorionicity, twin pregnancies with discordance at ultrasound, were more likely to have a small-for-gestational-age infant than concordant twin pregnancies (dichorionic: 51% vs 29%; P=.002; monochorionic: 65% vs 24%; P<.001). Furthermore, women with twin pregnancies with discordance were delivered at an earlier gestational age (dichorionic: 36 weeks [interquartile range, 33-36] vs 34 weeks [interquartile range, 34-38]; P<.001; monochorionic: 34 weeks [interquartile range, 32-34] vs 36 weeks [interquartile range, 34-37]; P=.003). Pregnancies with growth discordance were more likely to be delivered by cesarean delivery (dichorionic: 90% vs 72%; P=.01; monochorionic: 65% vs 60%; P=.70), although this was only statistically significant for dichorionic twin pregnancies. Neonates of pregnancies with growth discordance had a higher incidence of respiratory distress syndrome (dichorionic: 54% vs 37%; P=.04; monochorionic: 70% vs 45%; P=.04) and neonatal intensive care unit admission (dichorionic: 71% vs 50%; P=.01; monochorionic: 90% vs 65%; P=.03). Furthermore, dichorionic infants had longer neonatal intensive care unit stays (30 [interquartile range, 18-61] vs 18 [interquartile range, 10-35] days; P=.02).

CONCLUSION

Regardless of chorionicity, twin pregnancies with discordance without fetal growth restriction identified on growth ultrasound between 24 0/7 and 31 6/7 weeks' gestation were nearly twice as likely to develop small-for-gestational-age neonates, deliver earlier in gestation, and experience greater neonatal morbidity than twin pregnancies without discordance. Patients with pregnancies complicated by isolated intertwin discordance between 24 0/7 and 31 6/7 weeks' gestation will need counseling regarding adverse perinatal outcomes.

Second-trimester discordance and adverse perinatal outcome in twins: the STORK multiple pregnancy cohort

OBJECTIVE

The aim of this study was to determine the association between biometry discordance at the time of the anomaly scan and adverse perinatal outcomes in twin pregnancies.

DESIGN

Retrospective cohort study.

SETTING

Nine hospitals in the Southwest Thames Region of London Obstetric Research Collaborative (STORK).

POPULATION OR SAMPLE

Population multicentre retrospective study of all twin pregnancies booked for antenatal care in nine hospitals over a period of 10 years. Methods Logistic regression and receiver operating characteristic (ROC) curve analyses were performed to evaluate the association between abdominal circumference (AC) and estimated fetal weight (EFW) discordance, recorded between 20 and 22 weeks of gestation, and adverse pregnancy outcomes.

MAIN OUTCOME MEASURES

Stillbirth, neonatal mortality, preterm birth (PTB) at <34 weeks of gestation, and birthweight (BW) discordance ≥25%.

RESULTS

A total of 2399 twin pregnancies [457 monochorionic (MC) and 1942 dichorionic (DC)] were included in the study. The predictive accuracy of the EFW discordance was poor for fetal loss after 22 weeks of gestation (area under the curve, AUC 0.54, 95% CI 0.46-0.64), fetal loss beyond 28 weeks of gestation (AUC 0.42, 95% CI 0.31-0.52), perinatal loss (AUC 0.51, 95% CI 0.44-0.57), BW discordance (AUC 0.63, 95% CI 0.56-0.65), and PTB before 34 weeks of gestation (AUC 0.52, 95% CI 0.49-0.55). There was no significant difference in the prediction of these outcomes when using EFW discordance or AC discordance.

CONCLUSIONS

Once structural malformations, chromosomal abnormalities, and twin-to-twin transfusion syndrome have been excluded, second-trimester EFW and AC discordance have poor predictive value for adverse perinatal outcomes in twin pregnancy.

Ultrasound in twin pregnancies

OBJECTIVE

To review the literature with respect to the use of diagnostic ultrasound in the management of twin pregnancies. To make recommendations for the best use of ultrasound in twin pregnancies.

OUTCOMES

Reduction in perinatal mortality and morbidity and short- and long-term neonatal morbidity in twin pregnancies. Optimization of ultrasound use in twin pregnancies.

EVIDENCE

Published literature was retrieved through searches of PubMed and the Cochrane Library in 2008 and 2009 using appropriate controlled vocabulary (e.g., twin, ultrasound, cervix, prematurity) and key words (e.g., acardiac, twin, reversed arterial perfusion, twin-to-twin transfusion syndrome, amniotic fluid). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies. There were no date restrictions. Studies were restricted to those with available English or French abstracts or text. Searches were updated on a regular basis and incorporated into the guideline to September 2009. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The evidence collected was reviewed by the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada, with input from members of the Maternal Fetal Medicine Committee and the Genetics Committee of the SOGC. The recommendations were made according to the guidelines developed by The Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

The benefit expected from this guideline is facilitation and optimization of the use of ultrasound in twin pregnancy. SUMMARY STATEMENTS: 1. There are insufficient data to make recommendations on repeat anatomical assessments in twin pregnancies. Therefore, a complete anatomical survey at each scan may not be needed following a complete and normal assessment. (III) 2. There are insufficient data to recommend a routine preterm labour surveillance protocol in terms of frequency, timing, and optimal cervical length thresholds. (II-2) 3. Singleton growth curves currently provide the best predictors of adverse outcome in twins and may be used for evaluating growth abnormalities. (III) 4. It is suggested that growth discordance be defined using either a difference (20 mm) in absolute measurement in abdominal circumference or a difference of 20% in ultrasound-derived estimated fetal weight. (II-2) 5. Although there is insufficient evidence to recommend a specific schedule for ultrasound assessment of twin gestation, most experts recommend serial ultrasound assessment every 2 to 3 weeks, starting at 16 weeks of gestation for monochorionic pregnancies and every 3 to 4 weeks, starting from the anatomy scan (18 to 22 weeks) for dichorionic pregnancies. (II-1) 6. Umbilical artery Doppler may be useful in the surveillance of twin gestations when there are complications involving the placental circulation or fetal hemodynamic physiology. (II-2) 7. Although many methods of evaluating the level of amniotic fluid in twins (deepest vertical pocket, single pocket, amniotic fluid index) have been described, there is not enough evidence to suggest that one method is more predictive than the others of adverse pregnancy outcome. (II-3) 8. Referral to an appropriate high-risk pregnancy centre is indicated when complications unique to twins are suspected on ultrasound. (II-2) These complications include: 1. Twin-to-twin transfusion syndrome 2. Monoamniotic twins gestation 3. Conjoined twins 4. Twin reversed arterial perfusion sequence 5. Single fetal death in the second or third trimester 6. Growth discordance in monochorionic twins. Recommendations 1. All patients who are suspected to have a twin pregnancy on first trimester physical examination or who are at risk (e.g., pregnancies resulting from assisted reproductive technologies) should have first trimester ultrasound performed. (II-2A) 2. Every attempt should be made to determine and report amnionicity and chorionicity when a twin pregnancy is identified. (II-2A) 3. Although the accuracy in confirmation of gestational age at the first and second trimester is comparable, dating should be done with first trimester ultrasound. (II-2A) 4. Beyond the first trimester, it is suggested that a combination of parameters rather than a single parameter should be used to confirm gestational age. (II-2C) 5. When twin pregnancy is the result of in vitro fertilization, accurate determination of gestational age should be made from the date of embryo transfer. (II-1A) 6. There is insufficient evidence to make a recommendation of which fetus (when discordant for size) to use to date a twin pregnancy. However, to avoid missing a situation of early intrauterine growth restriction in one twin, most experts agree that the clinician may consider dating pregnancy using the larger fetus. (III-C) 7. In twin pregnancies, aneuploidy screening using nuchal transluscency measurements should be offered. (II-2B) 8. Detailed ultrasound examination to screen for fetal anomalies should be offered, preferably between 18 and 22 weeks' gestation, in all twin pregnancies. (II-2B) 9. When ultrasound is used to screen for preterm birth in a twin gestation, endovaginal ultrasound measurement of the cervical length should be performed. (II-2A) 10. Increased fetal surveillance should be considered when there is either growth restriction diagnosed in one twin or significant growth discordance. (II-2A) 11. Umbilical artery Doppler should not be routinely offered in uncomplicated twin pregnancies. (I-E) 12. For defining oligohydramnios and polyhydramnios, the ultrasonographer should use the deepest vertical pocket in either sac: oligohydramnios when < 2 cm and polyhydramnios when > 8 cm. (II-2B).

Discordant twins: diagnosis, evaluation and management

Approximately 16% of twin gestations have discordance of at least 20%. We identified 14 risk factors for divergent growth that can be categorized as maternal, fetal, or placental. Determination of chorionicity and serial ultrasound evaluation with a high index of suspicion for divergent growth is required for the diagnosis and stratification of risk. The highest reported likelihood ratio for detection of discordance was 5.9 during the first trimester examination and 6.0 for the second trimester. Although our ability to identify discordant twins is limited, once suspected and at viable gestational age, these pregnancies should have antepartum testing. Discordant growth alone is not an indication for preterm birth. Although there are multiple publications on the increased morbidity and mortality rates with discordant growth, there is a paucity of reports on how to manage them optimally and deliver them in a timely manner.

Growth abnormalities and multiple gestations

Growth abnormalities which include intrauterine growth restriction and weight discordance between twins are common in pregnancies complicated by multiple gestations and may be associated with poor perinatal outcomes. Knowledge of chorionicity is paramount when managing a multiple pregnancy. Monochorionic twins are at greater risk than dichorionic twins for growth issues, which may result in long-term complications including adverse neurological sequelae for the offspring. The purpose of the following article is to define normal and abnormal growth in multiples. In addition, the management of growth abnormalities in relationship to chorionicity will be discussed.

First and third trimester ultrasound in the prediction of birthweight discordance in dichorionic twins

OBJECTIVE

Birthweight discordance amongst twins is associated with an increase in perinatal morbidity and mortality. Clinical decisions regarding the management of twins are often made on the basis of estimated fetal weight in the third trimester. This study assesses the efficacy of routine third trimester ultrasound fetal biometry, third trimester fetal growth velocity and first trimester differences in size in the prediction of subsequent birthweight discordance.

STUDY DESIGN

Structurally and chromosomally normal dichorionic twin gestations resulting in two live births after 24 weeks gestation were identified. Ultrasound examinations of dichorionic twin pregnancies between 10 and 14 weeks of gestation were evaluated for inter-twin biometric disparity in crown-rump length (CRL). Estimated fetal weight (EFW) was calculated from the last scan before delivery. Fetal growth velocity (FGV) was calculated from two estimates of fetal weight between 21 and 35 days apart and incorporating the last EFW before delivery. EFW and FGV were expressed as standard deviation scores (Z scores). Disparity between these ultrasound parameters was correlated to inter-twin birthweight difference. Birthweight discordance was defined as > or =20% difference in birthweight relative to the heavier twin. Fishers exact and Spearman rho tests were used for statistical analysis. Test performance is expressed as area under the ROC curve and likelihood ratios (LR).

RESULTS

One hundred and thirty-five dichorionic gestations were identified over a consecutive 3-year-period. One hundred and eight twin gestations had both crown-rump length (CRL) and sufficient ultrasound measurements in the third trimester to calculate FGV. Twenty-six pregnancies (24%) had discordant birthweight. Only EFW Z score difference was correlated with birthweight disparity (r=0.36, p = <0.001). An EFW Z score difference of 0.6 had an area under the ROC curve of 0.70 (95% C.I. 0.59-0.79) but this did not differ significantly from first trimester prediction of growth discordance which had an area of 0.55 (95% C.I. 0.44-0.66). The LR for first and third trimester prediction of discordance were low.

CONCLUSION

Ultrasound measurement of fetal growth velocity and size both in the first and third trimesters is a poor predictor of birthweight discordance. Disparate fetal growth is exhibited as early as 10-14 weeks gestation and differences at this early stage in fetal development are no less accurate than EFW within 1 month of delivery. First trimester ultrasound, third trimester growth velocity and third trimester EFW do not accurately predict the delivery of twins with discordant birthweight.

Twin pregnancy: the role of ultrasound in management

Determination of chorionicity is one of the most important issues in the management of twin pregnancy. Modern ultrasound equipment has made it possible to accurately assess placentation already in the first trimester with the lambda sign. With regard to prenatal diagnosis, it is important to know the chorionicity in order to calculate the risk of chromosomally abnormal fetuses. Accurate chorionicity offers the obstetricians the opportunity to observe the monochorionic twins more intensively than is required for twins with dichorionic placentation. This review gives an update of the state of the art for clinicians caring for twin pregnancies.