Banks Claire L, Nelson Scott M, Owen Philip
Department of Obstetrics & Gynaecology, Princess Royal Maternity Unit, Glasgow Royal Infirmary, Alexandra Parade, Glasgow, UK.
Eur J Obstet Gynecol Reprod Biol. 2008 May;138(1):34-8. doi: 10.1016/j.ejogrb.2007.08.004. Epub 2007 Sep 25.
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.
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).
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.
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.
双胎出生体重不一致与围产期发病率和死亡率增加相关。关于双胎管理的临床决策通常基于孕晚期估计胎儿体重做出。本研究评估孕晚期常规超声胎儿生物测量、孕晚期胎儿生长速度以及孕早期大小差异在预测后续出生体重不一致方面的有效性。
确定妊娠24周后分娩出两个活产儿的结构和染色体正常的双绒毛膜双胎妊娠。评估孕10至14周双绒毛膜双胎妊娠的超声检查，以测量双胎间头臀长度（CRL）的生物测量差异。根据分娩前的最后一次扫描计算估计胎儿体重（EFW）。胎儿生长速度（FGV）根据相隔21至35天的两次胎儿体重估计值计算得出，并纳入分娩前的最后一次EFW。EFW和FGV以标准差分数（Z分数）表示。这些超声参数之间的差异与双胎出生体重差异相关。出生体重不一致定义为相对于较重双胎出生体重差异≥20%。采用Fisher精确检验和Spearman秩相关检验进行统计分析。检验效能以ROC曲线下面积和似然比（LR）表示。
在连续3年期间确定了135例双绒毛膜妊娠。108例双胎妊娠在孕晚期既有头臀长度（CRL）又有足够的超声测量值以计算FGV。26例妊娠（24%）出生体重不一致。只有EFW Z分数差异与出生体重差异相关（r = 0.36，p = <0.001）。EFW Z分数差异为0.6时，ROC曲线下面积为0.70（95%置信区间0.59 - 0.
