T. Dias

Cord entanglement and perinatal outcome in monoamniotic twin pregnancies

To assess the prevalence of cord entanglement and perinatal outcome in a large series of monoamniotic twin pregnancies and to review the recent literature on similar published large series.

Weight discordance and perinatal mortality in twins: analysis of the Southwest Thames Obstetric Research Collaborative (STORK) multiple pregnancy cohort

The degree of actual intertwin birth weight (BW) or ultrasound estimated fetal weight (EFW) discordance that justifies elective delivery is yet to be established. The main aim of this study was to ascertain the performance of BW and ultrasound EFW discordance in the prediction of perinatal loss in twin pregnancies.

First‐trimester ultrasound dating of twin pregnancy: are singleton charts reliable?

Please cite this paper as: Dias T, Mahsud‐Dornan S, Thilaganathan B, Papageorghiou A, Bhide A. First‐trimester ultrasound dating of twin pregnancy: are singleton charts reliable? BJOG 2010;117:979–984.

Prediction of selective fetal growth restriction and twin-to-twin transfusion syndrome in monochorionic twins.

Please cite this paper as: Memmo A, Dias T, Mahsud‐Dornan S, Papageorghiou A, Bhide A, Thilaganathan B. Prediction of selective fetal growth restriction and twin‐to‐twin transfusion syndrome in monochorionic twins. BJOG 2012;119:417–421.

Systematic labeling of twin pregnancies on ultrasound

Correct labeling of twin fetuses is needed for consistency in assigning and interpreting longitudinal scan and prenatal screening/diagnostic results. The aim of this study was to describe a standard method of twin labeling in the first trimester of pregnancy and to assess the robustness of such a technique in predicting the presenting twin in subsequent scans and at delivery.

Sri Lankan fetal/ birthweight charts: validation of global reference for fetal weight and birthweight percentiles.

INTRODUCTION Small for gestational age (SGA) is defined as birthweight below the tenth centile at a particular gestational week. Birthweight centiles for different populations are varied. Generic reference for fetal weight and birthweight that could be adapted to local populations was recently described. The purpose of this study was to validate the reference for birthweights adapted to the local population. METHODS This was a prospective validation study done between January 2012 and July 2012 in well dated pregnancies at General Hospital, Ampara. Observed frequencies of birthweights of 5th, 10th, 50th, 90th and 95th percentiles for Hadlock formula, World Health Organization (WHO) global survey data for Sri Lanka and India were calculated. The expected frequencies for each birthweight centile of our study were compared with observed frequencies. RESULTS A total of 411 patients were recruited and 207 delivered at 40 weeks (40+0-40+6). The mean birth-weight (SD) at 40 weeks of gestation was 3140g (432g). Hadlock formula and WHO reference data for India overestimate and underestimate most of the birthweights respectively. WHO generic reference adapted to Sri Lanka fitted well with our data. The mean birthweight of our population is similar, and the adapted reference range would identify most of the small fetuses correctly. It would also identify almost all the babies with weight above the 90th centile. CCONCLUSIONS The findings of the study show that the observed distribution of birthweight fitted well with the reference range derived from the WHO global reference range adapted to Sri Lankan population. WHO reference charts can be used effectively in Sri Lankan population.

Is first-trimester crown–rump length associated with birthweight?

Sir, We read with interest the article by Salomon et al. They studied 317 pregnancies conceived by in vitro fertilisation (IVF) and have suggested that differences in first-trimester crown–rump length (CRL) are associated with variations in birthweight. An argument is proposed suggesting that different growth trajectories become evident at 11–14 weeks of gestation. This is in contrast to larger first-trimester studies of multiple biochemical and biophysical parameters indicating that variation in CRL is not associated with variation in birthweight. We noted that the authors used the IVF treatment diary to date the pregnancies; they added 14 days to the date of oocyte retrieval. We wondered why they chose the date of oocyte retrieval and not the embryo replacement date for this purpose. Furthermore, what did they do in the instance of ovum donation or frozen embryos taken from several months or years before? How did they account for the variability in immediate versus blastocyst transfer with IVF? Some have suggested that a correction factor can be applied for the latter scenarios, but the accuracy of this correction relies entirely on the assumption that the embryonic growth rate is unchanged under different fertilisation regimens and during the early embryonic phase. Finally, did they account for the growth restricting effects of vanishing twins from spontaneously reducing multiple pregnancies? It is a simple fact that IVF treatment has now become so varied and complicated that we cannot presume that the oocyte retrieval dates are an accurate proxy for a natural cycle conception. Indeed, we examined over 400 IVF pregnancies and demonstrated that dating by the IVF treatment diary results in significant, but consistent differences in both first-trimester and second-trimester fetal biometry in singleton and twin pregnancies. To us, the obvious conclusion of these papers is that fertility treatment diaries cannot be reliably used to date IVF pregnancies. We wondered if the authors ever considered the possibility that their findings were the result of inaccurate dating from the IVF treatment diary rather than from differential fetal growth trajectories in the first trimester. Their own data show that there are systematic differences in the IVF population compared with natural conceptions. For example, the mean CRL and birthweight z-scores of the data should be 0, but they are negative for the first three quartiles. This may be a result of the inaccuracy of the equations used to calculate the z-scores, but is more likely to do with population dating. It is possible that if the pregnancies were dated by the CRL measurement, the association with birthweight would become non-significant. The authors could easily do this analysis, as it is a fairly simple statistical exercise to conduct on the data they already have. If the association between CRL and birthweight becomes non-significant, it would support the important assertion that we should date even IVF pregnancies by 11–14 weeks CRL measurements. The major objection to this policy is that it relies on the assumption that every baby is exactly the same length at the same duration of gestation. We make this assumption for spontaneously conceived pregnancies (National Institute for Clinical Excellence guidelines) to more accurately predict the most likely date of delivery in the context of an unknown date of conception. However, clinicians seem wedded to the practice of dating by conception date in IVF pregnancies despite mounting evidence that the latter is less reliable than ultrasound estimation. j

Use of ultrasound in predicting success of intrauterine contraceptive device insertion immediately after delivery

To assess by ultrasound examination the success of insertion of an intrauterine contraceptive device (IUD) immediately after delivery and to determine the optimal distance between the lower end of the IUD and the internal os in predicting successful retention of an IUD.

Accuracy of ultrasound estimated fetal weight formulae to predict actual birthweight after 34 weeks: prospective validation study

OBJECTIVES Late onset fetal growth restriction is often missed and is responsible for most intrauterine deaths. Ultrasound fetal biometry is routinely used to calculate estimated fetal weight (EFW). The aim of this study was to determine the accuracy of established ultrasound EFW formulae to identify small and large for gestational age fetuses when used after 35 weeks gestation. METHODS This was a prospective validation study done between January 2012 and July 2012 at General Hospital Ampara. An ultrasound examination was performed and fetal biometry was documented within one week before the delivery in well dated pregnancies. The mean of the differences between ultrasound EFW derived from 9 formulae and true birthweight and their standard error of mean (SE) were calculated for each formula. Systematic measurement error was assumed to exist if zero lay outside the mean difference ± 2SE. To show the EFW frequency distribution, z-scores were calculated as the number of standard deviations an observed EFW measurement deviated from the mean for gestation. RESULTS A total of 393 pregnancies at gestational age between 35 and 41 weeks were recruited. Mean gestational age at the ultra sound scan was 39.36 weeks SD (1.05). All EFW formulae either under or over estimated the birthweight in singleton pregnancies. Almost all the formulae overestimated the fetal weight in low birthweight babies whilst underestimating the fetal weight in birthweight >3500g. Campbell formula remained the only EFW formula without systematic error when measuring babies between 2500g and 3500g. None of the EFW z-scores were normally distributed. CONCLUSIONS This study found that all routinely used EFW formulae would either over or under estimate the fetal weight. Until an optimum EFW formula that suits the Sri Lankan population is determined, interpretation of ultrasound EFW should be done cautiously, especially in small for gestational age babies.

Elective birth at 37 weeks of gestation versus standard care for women with an uncomplicated twin pregnancy at term: the Twins Timing of Birth Randomised Trial

Sir, We read with interest the article by Dodd et al. They randomised a total of 235 women carrying twin pregnancies either to have elective birth at 37 weeks or standard care (planned birth from 38 weeks). They argue on the basis of their findings that in uncomplicated twin pregnancy, elective birth at 37 weeks of gestation was associated with a significant reduction in risk of serious adverse outcome for the infant. We applaud the authors for undertaking this important and challenging study, but wish to raise some points for consideration. We note that there is no mention of the method of gestational age assessment in the twin pregnancies recruited to the study. Accurate dating in early pregnancy is fundamental not only in routine clinical management of twin pregnancies, but also in determining the applicability of their data to the general population. Fairly robust evidence is now available that twin pregnancies can be accurately dated using crown–rump length between 11 and 14 weeks of gestation and by head circumference thereafter. The authors also failed to analyse the data according to the chorionicity of the twins. Recent, large cohort studies have demonstrated significantly higher stillbirth rates near term even in apparently low-risk monochorionic twin pregnancies. The latter may well justify a differential policy for the timing of delivery in monochorionic versus dichorionic twin pregnancies. Probably the most notable finding is that the majority of events labelled an ‘adverse outcome’ were birthweight less than the third centile (24/29 in standard care versus 7/11 in elective birth). Given that the latter is a relatively common finding in twin pregnancies and less commonly associated with real morbidity than in singletons, would the exclusion of this outcome variable leave the study adequately powered to truly evaluate the appropriate timing of birth in twin pregnancy? j References