Papageorghiou A T, Bakoulas V, Sebire N J, Nicolaides K H
Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, Denmark Hill, London, UK.
Ultrasound Obstet Gynecol. 2008 Dec;32(7):890-3. doi: 10.1002/uog.6140.
To examine birth weight in dichorionic and monochorionic twins and trichorionic triplets, and to estimate the relative independent importance on growth of fetal number, chorionicity and gestational age.
Four groups of pregnancies were examined: 12,816 singleton pregnancies, 302 monochorionic twin pregnancies, 569 dichorionic twin pregnancies, and 97 trichorionic triplet pregnancies. Chorionicity was determined at 10-14 weeks on the basis of the presence or absence of the lambda sign in twins, and by examining the ipsilon zone in triplets. The relationship between birth weight and gestational age in singletons was established, and using this equation the expected mean birth weights for all gestational ages were calculated. For each case in all groups, the difference between the observed birth weight for each fetus and the appropriate normal mean for gestation in singletons was calculated (Z-score). Multiple regression analysis was used to examine the independent contribution of gestational age, number of fetuses and chorionicity in the prediction of actual birth weight and birth weight Z-score.
Birth weight Z-score was significantly lower than the expected mean in singletons for dichorionic twins, monochorionic twins and trichorionic triplets (t = 15.4, P < 0.0001, t = 21.7, P < 0.0001 and t = 19.9, P < 0.0001, respectively). Furthermore, the reduction in expected birth weight was significantly greater for monochorionic twins and trichorionic triplets compared with dichorionic twins (t = 6.3, P < 0.0001 and t = 7.8, P < 0.0001, respectively). Multiple regression analysis demonstrated that number of fetuses, presence of a monochorionic placenta and gestational age were independently associated with birth weight Z-score, the strongest effect being fetal number, followed by monochorionicity (t = - 23.4, P < 0.0001, t = - 8.3, P < 0.0001 and t = - 4.9, P < 0.0001, respectively).
The finding that monochorionic twins were of lower adjusted birth weight than dichorionic twins, and the significant independent effect of chorionicity on birth weight suggest that monochorionic placentation in itself has an effect on intrauterine growth. The effect of fetal number independent of chorionicity is demonstrated by the lower birth weight of trichorionic triplets compared with dichorionic twins.
研究双绒毛膜双胎、单绒毛膜双胎及三绒毛膜三胎的出生体重，并评估胎儿数量、绒毛膜性及孕周对生长发育的相对独立重要性。
对四组妊娠情况进行研究：12816例单胎妊娠、302例单绒毛膜双胎妊娠、569例双绒毛膜双胎妊娠及97例三绒毛膜三胎妊娠。根据双胎中λ征的有无，以及三胎中ε区的检查结果，在孕10 - 14周确定绒毛膜性。建立单胎出生体重与孕周之间的关系，并使用该方程计算所有孕周的预期平均出生体重。对于所有组中的每一例，计算每个胎儿的观察出生体重与单胎相应正常孕周平均值之间的差异（Z评分）。采用多元回归分析来检验孕周、胎儿数量及绒毛膜性对实际出生体重及出生体重Z评分预测的独立贡献。
双绒毛膜双胎、单绒毛膜双胎及三绒毛膜三胎的出生体重Z评分均显著低于单胎的预期平均值（分别为t = 15.4，P < 0.0001；t = 21.7，P < 0.0001；t = 19.9，P < 0.0001）。此外，与双绒毛膜双胎相比，单绒毛膜双胎和三绒毛膜三胎预期出生体重的降低更为显著（分别为t = 6.3，P < 0.0001；t = 7.8，P < 0.0001）。多元回归分析表明，胎儿数量、单绒毛膜胎盘的存在及孕周与出生体重Z评分独立相关，其中胎儿数量的影响最强，其次是单绒毛膜性（分别为t = - 23.4，P < 0.0001；t = - 8.3，P < 0.0001；t = - 4.9，P < 0.0001）。
单绒毛膜双胎经调整后的出生体重低于双绒毛膜双胎，且绒毛膜性对出生体重有显著独立影响，这表明单绒毛膜胎盘本身对子宫内生长有影响。三绒毛膜三胎出生体重低于双绒毛膜双胎，证明了胎儿数量独立于绒毛膜性的影响。
