| Popis: |
First and second trimester gestational age assessment in twins can be reliably done using singleton crown rump length and head circumference charts, respectively. It is logical to use the biometry of the bigger twin for this purpose as pathological largeness is an unlikely event in early pregnancy. Chorionicity determines the pregnancy outcome of twin pregnancy. Use of first trimester ultrasound markers; number of placental masses lambda and 'T' sign is highly sensitive and specific for the determination of chorionicity. Orientation of the fetuses in twin pregnancy is vital for consistent growth assessment and invasive procedures. Routinely, twins are labelled according to the relative position of the gestational sac which they contain in relation to maternal cervix. However, considerable number of fetuses changes their presenting and birth order in subsequent scan and at birth respectively. Therefore, it is wise to label twins according to their relative position within the uterus by either left! right (lateral orientation) or top/ bottom (vertical orientation). It has long been recognised that monoamniotic (MA) twins carry very high perinatal morbidity and mortality. Because of this presumed high perinatal mortality, MA twins tend to deliver early. Cord entanglement has been attributed mostly for these losses; however, cord entanglement is a universal finding in MA pregnancies if it has been systematically evaluated by ultrasound. Moreover, most of the pregnancy losses in MA twins are secondary to structural anomalies, twin reverse arterial perfusion (TRAP) and conjoint twining which often can be diagnosed in early ultrasound scan. Once these attributed fetal causes (structural anomalies, TRAP and conjoined twining) have been excluded, fetal survival in MA twins is similar to monochorionic diamniotic twins (MCDA). It is difficult to support a policy for differential timing of delivery in MA and MCDA twin pregnancies. Early pregnancy growth variation has been thought to be valuable in predicting late pregnancy complications. But predictive ability of CRL discrepancy and subsequent fetal loss or birthweight discordance is poor. There is no difference in CRL discordance in dichorionic diamniotic (DCDA) and MCDA twins. However, in depth analysis of CRL discrepancy and specific MCDA complications revealed that selective fetal growth restriction (sFGR) can be reliably screen during fist trimester by CRL discrepancy. If the discrepancy is ~7% the sensitivity would be > 90% for subsequent development of sFGR in MCDA twins. |
