A Critical Assessment of Antenatal Monitoring for Fetal Well-Being in Down Syndrome Pregnancies.

Background/Objectives: The antenatal management of Down syndrome (DS) is difficult as it is associated with a high risk for in utero fetal demise (IUFD) with a paucity of literature to guide antenatal surveillance. Avoidance of preterm delivery in the DS fetus, so commonly affected by anomalies, compounds the dichotomy of achieving term delivery while balancing against the risk for IUFD as gestational age advances. Higher-performing tests are needed to predict, and, thus, hopefully prevent, both preterm delivery and fetal mortality. Our study was undertaken to evaluate the performance metrics of current antenatal surveillance parameters that might suggest an increased risk for IUFD. Methods: We studied a retrospective cohort of all continuing pregnancies with a cytogenetically confirmed DS fetus between 2009 and 2019 at a single institution. Cases were investigated for abnormalities in fetal growth, anatomy, UA Doppler, and amniotic fluid volume to analyze their interrelationships and their association with the primary outcome, IUFD. Nonstress testing (NST) and biophysical profile data as available were also reviewed for analysis on each case. Maternal demographic data were also collected. Results: A total of 41 DS pregnancies at >20 weeks gestation were included. Eight (19.5%) resulted in IUFD, while thirty-three (80.5%) resulted in live birth. Between these groups, there was no significant difference in the incidence of fetal structural anomalies. FGR was present in 8/41 fetuses or 19.5% of all cases. FGR was present in 1 of 8 (12.5%) IUFD cases and 7 of 33 (21.2%) live births (p = 0.50). Thus, notably, 87.5% (7/8) of the IUFDs occurred in the absence of FGR. Furthermore, 1/8 (12.5%) FGR cases resulted in IUFD vs. 7/33 (21.2%) of non-FGR cases (p = 0.50). In DS fetuses after 24 weeks gestation, UA Doppler abnormalities developed in 75% of FGR cases (6/8) and in 64.5% of normally grown cases (20/31) (p = 0.33). Abnormal UA Dopplers were noted in 83.3% of IUFD and in 84.8% of liveborn cases (p = 0.34). Eleven of thirty-three live births, however, underwent iatrogenic delivery secondary to worsening fetal surveillance, including ten with worsening UA Doppler indices. There was an increased frequency of abnormal NST in the IUFD group (66.7% vs. 23.8%), although this difference did not reach statistical significance. Polyhydramnios was more frequent in the IUFD group (62.5% vs. 16.1%, p = 0.04). Conclusions: Aside from polyhydramnios, no fetal surveillance parameter demonstrated an association with IUFD that reached statistical significance. A majority of fetuses with DS are normally grown and demonstrate abnormal UA Doppler indices in the absence of FGR. Within our cohort, a substantial number of liveborn deliveries were prompted following worsening UA Dopplers. Both polyhydramnios and UA Doppler indices are worthy of further investigation to inform clinically useful fetal surveillance strategies in DS.