234: Incidence of adverse pregnancy outcomes based on mode of conception in monochorionic diamniotic twins

To compare the incidence of monochorionic diamniotic (MCDA) twin-specific complications in spontaneous versus assisted reproductive technology (ART)-conceived MCDA twin pregnancies. This was a retrospective cohort study of all MCDA pregnancies followed at a maternal fetal medicine center between January 1, 2012 and July 15, 2017. Exclusion criteria were structural anomalies, chromosomal abnormalities, or intrauterine fetal demise prior to 16 weeks. MCDA twin pregnancies were divided into two groups: spontaneous or conceived by ART. The primary outcome was development of twin-to-twin transfusion syndrome (TTTS), twin anemia polycythemia sequence (TAPS), or selective intrauterine growth restriction (sIUGR). The student t-test and the chi(2) test were used to compare categorical variables and means. Inter-correlations between variables (namely MCDA complications) were investigated by Spearman rank correlation. Ninety-one MCDA twin pregnancies met inclusion criteria. Of these pregnancies, 64 (70.3%) were conceived spontaneously and 27 (29.6%) were conceived by ART. Maternal age was significantly higher in the ART group (p < 0.001) and body mass index was significantly lower (p < 0.01). Women who had conceived by ART were more likely to identify as white (47% versus 21%, p<0.05) and carry a medical comorbidity unrelated to a MCDA pregnancy, namely thyroid and autoimmune disease (p<0.05). Overall, 9.9% of all MCDA twins developed TTTS: 12.5% versus 3.7%, from the spontaneous versus ART group respectively (r = -0.13, p = 0.72). Seven pregnancies (7.7%) were complicated by TAPS: 9.3% spontaneous conceptions versus 3.7% ART conceptions (r=-0.09, p=0.19). Thirty (33%) pregnancies developed sIUGR: 34% versus 29.6% (r=-0.03, p=0.10). MCDA pregnancies conceived by ART were more likely to undergo a caesarean section (p<0.05) with no difference in gestational age of delivery (mean 34 weeks, p=0.34). Conception via fertility treatment does not appear to increase the incidence of MCDA-specific pregnancy complications.