Twin Pregnancies, Crown-rump Length and Birthweight Discordancy: The Influence of Chorionicity

Abstract Objective The purpose of the present study was to analyze the influence of chorionicity in the biometric parameters crown-rump length (CRL), birthweight (BW), crown-rump length discordancy (CRLD) and birthweight discordancy (BWD), determine the correlation between these latter two in cases of intertwin discordancy, and to analyze the influence of chronicity in the presence of these discordancies with clinical relevance (> 10% and > 15%, respectively). Methods The present study was a retrospective study based on the twin pregnancy database of the Centro Hospitalar S. João (2010-2015), including 486 fetuses among 66 monochorionic (MC) and 177 dichorionic gestations (DC). The inclusion criteria were multiple pregnancies with 2 fetuses and healthy twin gestations. The exclusion criteria were trichorionic gestations and pregnancies with inconclusive chorionicity, multiple pregnancy with ≥ 3 fetuses and pathological twin gestations. Results No statistically significant difference was found in BW (p = 0.09) and in its discordancy (p = 0.06) nor in CRL (p = 0.48) and its discordancy (p = 0.74) between MCs and DCs. Crown-rump length discordancy and birthweight discordancy were correlated by the regression line “BWD = 0.8864 x CRLD + 0.0743,” with r2 = 0.1599. Crown-rump length discordancy > 10% was found in 7.58% of monochorionic and in 13.56% of dichorionic twins. Birthweight discordancy > 15% was detected in 16.67% of monochorionic and in 31.64% of dichorionic twins. Conclusion No statistically significant influence of chorionicity was identified in both birthweight and birthweight discordancy, as in crown-rump length and crown-rump length discordancy. Birthweight discordancy was correlated to crown-rump length discordancy in 20% of cases.

### 摘要
#### 研究目的
本研究旨在分析绒毛膜性（chorionicity）对顶臀长（crown-rump length, CRL）、出生体重（birthweight, BW）、顶臀长不一致性（crown-rump length discordancy, CRLD）及出生体重不一致性（birthweight discordancy, BWD）这些生物学参数的影响；明确双胎间不一致病例中后两项指标间的相关性；并分析存在具有临床相关性的上述不一致性（分别为差异>10%和>15%）时绒毛膜性的影响作用。
#### 研究方法
本研究为回顾性研究，基于圣若昂中心医院（Centro Hospitalar S. João）2010-2015年的双胎妊娠数据库开展，共纳入66例单绒毛膜（monochorionic, MC）妊娠与177例双绒毛膜（dichorionic, DC）妊娠，总计486例胎儿。纳入标准为：含2个胎儿的多胎妊娠且为健康双胎妊娠；排除标准包括：三绒毛膜（trichorionic）妊娠、绒毛膜性判定不明的妊娠、胎儿数≥3的多胎妊娠以及病理性双胎妊娠。
#### 研究结果
单绒毛膜与双绒毛膜双胎在出生体重（p=0.09）、出生体重不一致性（p=0.06）、顶臀长（p=0.48）及顶臀长不一致性（p=0.74）方面均未发现具有统计学意义的差异。顶臀长不一致性与出生体重不一致性的回归方程为"BWD = 0.8864 × CRLD + 0.0743"，决定系数r²=0.1599。顶臀长不一致性>10%的病例在单绒毛膜双胎中占比7.58%，在双绒毛膜双胎中占比13.56%；出生体重不一致性>15%的病例在单绒毛膜双胎中占比16.67%，在双绒毛膜双胎中占比31.64%。
#### 研究结论
本研究未发现绒毛膜性对出生体重、出生体重不一致性，以及顶臀长、顶臀长不一致性存在具有统计学意义的影响。约20%的病例中，出生体重不一致性与顶臀长不一致性存在相关性。