Association Between Twin Discordance at 6–9 Weeks' of Gestation and Birthweight Complications

Crown-rump length discordance and adverse perinatal outcome in twin pregnancies: systematic review and meta-analysis

OBJECTIVE

The aim of this systematic review was to explore the relationship between crown-rump length (CRL) discordance detected at 11-14 weeks of gestation and adverse outcome in twin pregnancy and to assess its predictive accuracy.

METHODS

A protocol designed a priori following MOOSE guidelines and recommended for systematic review and meta-analysis was used. The outcomes observed were: total fetal and perinatal loss, fetal loss at <24 weeks, fetal loss at ≥ 24 weeks, birth-weight (BW) discordance, preterm delivery (PTD) at < 34 weeks and fetal anomalies. The analysis was performed for all twins and for dichorionic (DC) and monochorionic (MC) twins separately.

RESULTS

A total of 2008 articles were identified and 17 studies were included in the systematic review. Twin pregnancies with CRL discordance ≥ 10% were at significantly higher risk of perinatal loss (RR, 2.80; 95% CI, 1.25-6.27; P = 0.012), fetal loss at ≥ 24 weeks (RR, 4.07; 95% CI, 1.47-11.23; P = 0.006), BW discordance (RR, 2.24; 95% CI, 1.89-2.64; P < 0.001) and PTD at < 34 weeks (RR, 1.49; 95% CI, 1.23-1.80; P < 0.001) but not of fetal loss at < 24 weeks (P = 0.130). A meta-analysis of fetal anomalies was not possible because fewer than two studies explored this outcome. However, when used alone to screen for adverse pregnancy outcome, the predictive accuracy of CRL discordance was low for each of the outcomes explored.

CONCLUSION

CRL discordance is associated with an increased risk of adverse pregnancy outcome. However, the accuracy of CRL discordance in predicting adverse outcome is poor and thus limits its routine use in clinical practice.

First-trimester growth discordance and adverse pregnancy outcome in dichorionic twins

OBJECTIVE

To evaluate the association between first-trimester growth discordance and adverse pregnancy outcome in dichorionic twin pregnancies.

METHODS

This was a retrospective cohort study of consecutive women with dichorionic twin pregnancies undergoing an ultrasound scan at our institution between 7 and 14 weeks' gestation. Study groups were defined by the presence or absence of ≥ 11% crown-rump length (CRL) discordance. Pregnancies were excluded if one twin was dead on initial ultrasound or if a termination was performed. The primary outcome was loss of one or both fetuses before 20 weeks. Secondary outcomes included fetal anomaly, fetal demise after 20 weeks (stillbirth), small-for-gestational-age (SGA) at birth, admission to the neonatal intensive care unit (NICU) and preterm delivery before 34 weeks.

RESULTS

Of 805 dichorionic twin pregnancies undergoing first-trimester ultrasound, 610 met the inclusion criteria. Eighty-six had ≥ 11% CRL discordance and, of these, nine (10.5%) had a fetal loss at < 20 weeks (risk ratio (RR) 7.8 (95% CI, 3.0-20.5)). In the surviving pregnancies, an increased risk of fetal anomalies was seen (27.3 vs 17.4%, RR 1.6 (95% CI, 1.1-2.4)). In surviving pregnancies unaffected by anomalies, no increased risk of stillbirth, SGA, NICU admission or delivery before 34 weeks was noted in the discordant group. A post-hoc power analysis demonstrated 80% power to detect a five-fold increase in the risk of stillbirth and 90% power to detect a two-fold increase in other outcomes.

CONCLUSION

Dichorionic pregnancies in which a CRL discordance of at least 11% is noted are at increased risk for fetal anomalies and fetal loss prior to 20 weeks' gestation. However, patients can be reassured that, in the absence of structural anomalies, CRL discordance does not appear to be associated with other adverse outcomes in continuing pregnancies, although the power to detect small increases in the risk of stillbirth may have been limited by the sample size.