Spencer Kevin, Kagan Karl O, Nicolaides Kypros H
Prenatal Screening Unit, Clinical Biochemistry Department, King George Hospital, Goodmayes, UK.
Prenat Diagn. 2008 Jan;28(1):49-52. doi: 10.1002/pd.1923.
To examine the distribution of first-trimester biochemical markers of aneuploidy in twin pregnancies, and to assess whether there are differences in the distributions between monochorionic and dichorionic twins.
Maternal serum-free beta-hCG and PAPP-A were measured between 11 + 0 and 13 + 6 weeks as part of a routine first-trimester screening program in conjunction with fetal nuchal translucency (NT) performed at two sites. Data from twin pregnancies were extracted from the fetal databases along with information on the chorionicty. The individual marker concentrations were expressed as weight corrected, ethnicity corrected, smoking corrected and IVF corrected MoM using data from singleton pregnancies as the reference. The overall medians were compared to those in singleton pregnancies and between monochorionic and dichorionic twins.
Data was available from 1914 sets of twins. Of these, 1214 had information with respect to chorionicity, with 1024 being dichorionic and 190 being monochorionic. The overall median weight corrected, ethnicity corrected, smoking corrected and IVF corrected MoM amongst twin pregnancies were 2.023 for free beta-hCG (sd log(10) MoM = 0.2611 and 2.121 for PAPP-A (sd log(10) MoM = 0.2255) -- both medians were significantly greater than the medians in singleton pregnancies (1.00 MoM). In the case of monochorionic and dichorionic twins the median weight corrected, ethnicity corrected, smoking corrected and IVF corrected, free beta-hCG MoM's were not significantly different (1.983 v 2.041), however for PAPP-A the median weight corrected, ethnicity corrected, smoking corrected and IVF corrected MoM in monochorionic twins was significantly lower than in dichorionic twins (1.756 v 2.250) whilst the sd log(10) MoM's were not significantly different (0.2185 v 0.2167).
Screening in twin pregnancies requires adjustment of the calculated MoM to account for the presence of two fetuses. In general, for free beta-hCG, this should be by dividing the observed corrected MoM by 2.023. For PAPP-A two different factors are required - 2.192 in dichorionic twins and 1.788 in monochorionic twins.
研究双胎妊娠孕早期非整倍体生化标志物的分布情况，并评估单绒毛膜双胎和双绒毛膜双胎之间的分布是否存在差异。
在11+0至13+6周期间测定孕妇血清游离β-hCG和妊娠相关血浆蛋白-A（PAPP-A），这是一项常规孕早期筛查项目的一部分，同时在两个地点进行胎儿颈部透明带（NT）检查。从胎儿数据库中提取双胎妊娠的数据以及绒毛膜性信息。使用单胎妊娠数据作为参考，将个体标志物浓度表示为体重校正、种族校正、吸烟校正和体外受精校正的中位数倍数（MoM）。将总体中位数与单胎妊娠以及单绒毛膜双胎和双绒毛膜双胎之间的中位数进行比较。
有1914对双胎的数据。其中，1214对有绒毛膜性信息，1024对为双绒毛膜双胎，190对为单绒毛膜双胎。双胎妊娠中总体体重校正、种族校正、吸烟校正和体外受精校正的游离β-hCG MoM中位数为2.023（标准差log(10) MoM = 0.2611），PAPP-A为2.121（标准差log(10) MoM = 0.2255）——两者中位数均显著高于单胎妊娠的中位数（1.00 MoM）。对于单绒毛膜双胎和双绒毛膜双胎，体重校正、种族校正、吸烟校正和体外受精校正的游离β-hCG MoM中位数无显著差异（1.983对2.041），然而对于PAPP-A，单绒毛膜双胎中体重校正、种族校正、吸烟校正和体外受精校正的MoM中位数显著低于双绒毛膜双胎（1.756对2.250），而标准差log(10) MoM无显著差异（0.2185对0.2167）。
双胎妊娠筛查需要调整计算出的MoM以考虑两个胎儿的存在。一般来说，对于游离β-hCG，应将观察到的校正MoM除以2.023。对于PAPP-A，则需要两个不同的因子——双绒毛膜双胎中为2.192，单绒毛膜双胎中为1.788。
