Abstract
To evaluate the impact of discordant Crown Rump Length (CRL) noted in the first trimester
on the outcome of monochorionic (MC) and dichorionic (DC) twin gestations and to establish
it's role as a predictor of adverse outcomes. This was a retrospective case control
study carried out at a tertiary fetal medicine centre in South India between June
2013 and May 2018. Cases were obtained from the database of the centre. All viable
monochorionic diamniotic (MCDA) and dichorionic diamniotic (DCDA) twin pregnancies
scanned between 11 and 14 weeks gestational age after excluding fetuses with structural
abnormalities were included in the study. The impact of discordant CRL ≥ 10% on the
outcomes of twins was evaluated. Among 2627 twin pregnancies 2298 (87.5%) were dichorionic
and 329 (12.5%) were monochorionic. Among the DC twin pregnancies CRL discordance
≥ 10% was found in 124 (5.4%) while 2174 (94.6%) were concordant. Among the MC twin
pregnancies CRL discordance ≥ 10% was found in 20 (6.1%) while 309 (93.9%) were concordant.
In DC twin pregnancies we found a significant association between CRL discordance
of ≥ 10% and fetal loss (p = 0.001), mean GA at delivery (p = 0.002) and mean birth weight (p = 0.04). However in MC twin pregnancies we did not find any association between discordant
CRL and adverse outcomes. When the CRL discordance cutoff was increased to ≥ 16% (95th
centile), there was a significant increase in the aforementioned adverse outcomes
in DC twin pregnancies while in MC twin pregnancies there was a significant increase
in fetal loss (p = 0.027). To evaluate CRL discordance as a predictor of adverse outcomes, receiver
operating curves were created for each outcome studied. But they failed to show the
predictive accuracy in both CRL ≥ 10% and CRL ≥ 16% groups. CRL discordance in DC
twin pregnancies are more commonly associated with adverse outcomes than MC twin pregnancies
and it significantly increases when CRL C 16% (95th centile) was used as cutoff. Hence
CRL discordance of ≥ 16% should be set as the cutoff to identify pregnancies at risk.
However we reiterate that discordant CRL, irrespective of the cutoff used, is not
a robust predictor of adverse outcomes.
Keywords
CRL discordance - Twin pregnancy - Adverse pregnancy outcome - Fetal loss - Preterm
delivery - Birthweight discordance
