The Predictive Value Of NT,CRL And Amniotic Fluid Maximum Depth Discrepancy For Twin-twin Transfusion Syndrome

BackgroundTwin-twin transfusion syndrome(TTTS)is a serious complication of monochorionic diamniotic(MCDA)twin pregnancy,the incidence is 10%?15%[1].At present,the pathogenesis of TTTS has not been fully understood,and the form of vascular anastomosis between placentas is the anatomical basis of twin blood transfusion.The placenta of most monochorionic twins has more than one anastomotic vessel.There are three types of Anastomoses,including arterial-arterial anastomoses,venous-venous anastomoses and arterial-venous anastomoses.Monochorionic twins share one placenta,when the placental vascular anastomoses distribution is abnormal or abnormal placental area distribution,the supplying fetus will continue to deliver blood to the receiving fetus through the anastomotic branches of blood vessels of the placenta,and then TTTS will occur.Without timely clinical intervention,TTTS can often lead to serious complications associated with premature delivery or one or two intrauterine deaths.The perinatal mortality of TTTS without intrauterine treatment was up to 70%?90%[2-5].TTTS is caused by unbalanced blood transfusion between twins through placental vascular anastomotic branch,low blood volume of supplying fetus and high blood volume of receiving fetus lead to oligohydramnios of supplying fetus and polyhydramnios of receiving fetus.At the same time,changes in renin-angiotensin cascale caused by high blood volume of the receiving fetus and low blood volume of the supplying fetus exacerbated the imbalance in amniotic fluid volume.Differences in amniotic fluid volume in MCDA twin pregnancies that do not meet the diagnostic criteria for TTTS may have begun to occur before the occurrence of TTTS[1-6].However,whether the difference of amniotic fluid volume has predictive value for the occurrence of TTTS and what is the critical value of amniotic fluid volume difference that can better predict the subsequent occurrence of TTTS has not been fully elucidated.In addition,although it has been reported that the early signs of TTTS hemodynamic imbalance can be expressed as the increase of nuchal translucency(NT)thickness,or the increase of intertwin discrepancy in NT or crown rump length(CRL),and the occurrence of TTTS was predicted early by NT difference and CRL difference between twins,the data results published so far are not uniform[7,8].MCDA twins pregnancy are prone to serious complications of TTTS,and untreated TTTS twins have a higher perinatal mortality rate.If we can predict the high risk population of TTTS in MCDA twin pregnancy,and then diagnose TTTS in time,it will be helpful to strengthen the management of pregnancy,select the suitable clinical treatment plan and carry on the early clinical intervention,to improve the outcome of MCDA twin pregnancy.Therefore,early prediction of TTTS is of great significance.ObjectiveTo investigate the value of intertwin discrepancy in NT value,CRL,amniotic fluid maximum depth in the first trimester and amniotic fluid maximum depth in the second trimester for early prediction of TTTS in MCDA twin pregnancy,and to find the best index for early prediction of TTTS.To provide more evidence for the early diagnosis and management of pregnancy of Twin-twin Transfusion Syndrome,and to improve the pregnancy outcome and perinatal outcome of twin pregnancy with Twin-twin transfusion syndrome.Materials and methods1 Research ObjectsA retrospective statistical analysis of cases diagnosed with MCDA twin pregnancy by ultrasound at the Third Affiliated Hospital of Zhengzhou University,from 1 January 2013 to 31 January 2019.The collected cases were grouped by inclusion criteria and exclusion criteria.All the cases underwent placental pathological examination after vaginal delivery,cesarean section or induction of labor.Combined with the growth and development of perinatal babies,25 MCDA twin pregnant women with TTTS were finally diagnosed as the case group,and 249 MCDA twin pregnant women with no complications at the same period were studied as the control group.1.1 Inclusion criteriaTwo groups of common group criteria:(1)MCDA twin pregnancy was managed in the Third Affiliated Hospital of Zhengzhou University from the first trimester to delivery;(2)NT value,CRL,amniotic fluid maximum depth at 11-13+6 weeks of gestation and amniotic fluid maximum depth at 16-26 weeks of gestation were complete,and the CRL ranges from 45 mm to 84 mm.(3)Ultrasound graphic data in in the first trimester,the second trimester and the third trimester pregnancy and clinical data before and after admission were complete.Other inclusion criteria of the control group:no MCDA twin pregnancy-related complications.Other inclusion criteria for the case group:no MCDA twin pregnancy-related complications other than TTTS were found when TTTS was diagnosed.1.2 Exclusion criteria(1)Pregnant women with severe systemic organ disease or family major genetic history.(2)Fetuses with major structural abnormalities or Chromosome abnormality.(3)Twin anemia-polycythemia sequence(TAPS),twin reversed arterial perfusion sequence(TRAPS),selective intrauterine growth restriction(sIUGR),intrauterine fetal death(IUFD)and other complications are complicated.(4)One of the twins nearly has no amniotic fluid or complicated with placental disease.2 Relate MaterialsTo collect the basic clinical information of each group,including the cases of the first trimester and the second trimester ultrasound examination and admission to hospital until delivery of clinical data.By consulting case data and telephone follow-up,we recorded the pregnant woman's age,gravidity and parity history,method of conception,mode of delivery,NT value,CRL,amniotic fluid maximum depth,the gestational age of ultrasonography,the gestational age of TTTS was diagnosed,the gestational age of delivery,the number of IUFD and the number of deliveries before 37 weeks.3 Research methods3.1 related definitions(1)According to the rule of fetal growth and development,the time of fetal ultrasound screening in the first trimester was located at 11-13+6 weeks[9].(2)According to ISUOG clinical guidelines,single chorionic twins without complications were examined by ultrasonography every two weeks from the 16th week of Gestation[24],so the duration of mid-term ultrasound examination was 16-26 weeks.(3)NT difference between twins:intertwin NT difference value equal to larger NT value minus smaller NT value.CRL difference between twins:intertwin CRL difference value equal to larger CRL minus smaller CRL.The discrepancy of amniotic fluid volume between twins:intertwin amniotic fluid volume difference value equal to larger amniotic fluid maximcon depth minus smaller amniotic fluid maximcon depth.In addition,the amniotic fluid volume of the two fetuses measured in the first trimester and the second trimester did not meet the diagnostic TTTS standard,that is there was a difference in amniotic fluid volume between the twins,but it did not meet the maximum amniotic fluid depth of the blood supplying fetus<2cm,while the maximum amniotic fluid depth of the blood receiving fetus before 20 weeks was>8cm or the maximum amniotic fluid depth of the blood receiving fetus after 20 weeks was>10cm.3.2 statistical methodsSPSS21.0 software was used to carry out statistical analysis of the data,the measurement data that obeyed the normal distribution were expressed by mean and standard deviation(x±s),the two groups were compared by t test.And the measurement data that did not obey the normal distribution were expressed by median and quartile[M(Q1,Q3)],nonparametric rank sum test(Manny-Whitely U test)was used to compare the two groups.The adoption rate of counting data was expressed,and the x 2 test was used for the comparison of counting data between the two groups.The intertwin NT difference value,CRL difference value,the difference value of amniotic fluid volume in the first trimester and the difference value of amniotic fluid volume in the second trimester were calculated,and the index of the case group and the control group were compared to determine the statistical significance of the data between two groups;The optimal cut-off value of NT difference value,CRL difference value,the difference value of amniotic fluid volume in the first trimester and the difference value of amniotic fluid volume in the second trimester were evaluated by ROC curve.The sensitivity,specificity,positive predictive value,negative predictive value and area under ROC curve were also evaluated,to explore the predictive value of each index to the occurrence of TTTS,the test level is a=0.05.Results1 comparison of general dataThe NT difference value of the fetus in the case group was[0.6(0.2,1.0)mm]greater than that in the control group[0.2(0.1,0.3)mm].The difference value of amniotic fluid volume in the case group was[57.0(28.0,69.0)mm],which was significantly larger than that in the control group[6.0(3.0,11.0)mm].The gestational week of parturition in the case group[(30.2±5.2)weeks]was earlier than that in the control group[(35.9±2.1)weeks](p<0.05).There were statistically significant differences in the mode of delivery,the number of subsequent IUFD occurred and the number of deliveried before 37 weeks between the two groups(p<0.05).There were no significant differences in CRL value,the difference of amniotic fluid volume in the first trimester,the first trimester screening gestational age,the second trimester screening gestational age,the pregnant woman's age,gravidity and parity history,method of conception between the two groups(p>0.05).2 Analysis of the predictive value of NT,CRL and amniotic fluid maximcon depth discrepancy in pregnancy on TTTS(1)When the optimal NT cut-off value was 0.6 mm,the AUC of predicting TTTS in MCDA twin pregnancy was 0.730(95%CI:0.601-0.858(P<0.05)),the sensitivity,specificity,positive and negative predictive value were 52.0%,94.0%,46.4%and 95.1%respectively.(2)There was no predictive value of CRL for TTTS in MCDA twin pregnan cy(P>0.05).(3)The difference of amniotic fluid volume in the first trimester had no statistical significance in predicting TTTS in MCDA twin pregnancy(P>0.05).(4)When the optimal cut-off value of the amniotic fluid volume difference during the second trimester was 25mm,the AUC was 0.905(95%CI:0.798-1.0)(P<0.05),the sensitivity,specificity,positive predictive value and negative predictive value of TTTS were 88.0%,94.0%,59.5%and 98.7%respectively.(5)When NT difference?0.6 mm and amniotic fluid volume difference?25 mm in the second trimester(P<0.05),the sensitivity,specificity,positive predictive value and negative predictive value of MCDA twin pregnancy TTTS were 48.0%,99.6%,91.7%and 94.7%respectively.Conclusion1 In MCDA twin pregnancy,the difference of NT value between twins in the first trimester has early prediction value for TTTS,and the difference of amniotic fluid maximcon depth in the second trimester has prediction value for TTTS.The difference of amniotic fluid maximcon depth during the second trimester predicted the occurrence of TTTS best.2 The difference of amniotic fluid maximcon depth and CRL in the first trimester had no significant predictive value for TTTS in MCDA twin pregnancy.