Postnatal Outcomes of Monochorionic Diamniotic Twins versus Dichorionic Diamniotic Twins

Background: It is commonly accepted that postnatal outcomes for twins are dependent on their chorionicity. However, few studies describe the short-term and long-term outcomes of monochorionic diamniotic (Mo Di) twins as compared to dichorionic diamniotic (Di Di) twins. The purpose of this study was to evaluate the differences in outcomes among Mo Di and Di Di twins admitted to the NICU. Primary outcomes evaluated include length of NICU admission and length of respiratory support. Methods: A retrospective chart review of birthing people and their respective Mo Di and Di Di twins admitted to the NICU between 2019 and 2022 at the University of Missouri was conducted after approval by our International Review Board. Demographic information and short-term outcomes were collected. Chorionicity, receipt of antenatal steroids, receipt of prenatal magnesium sulfate, prenatal health data, prenatal ultrasound findings of the twins, reason for delivery, and mode of delivery were obtained from the birthing persons’ charts. Gestational age was collected in completed weeks of gestation at birth. Postnatal growth parameters were determined using Fenton charts. Outcome data of twins were obtained from neonates’ charts. Bronchopulmonary dysplasia (BPD) was characterized using the Jensen 2019 definition. Continuous variables and binomial variables were analyzed using the Kruskal-Wallis test and the Chi-Square tests, respectively. A p-value of <0.05 was used to define significance. Linear regression analysis using birthing persons’ and neonates’ variables was performed using SPSS version 28 (IBM SPSS Statistics, IBM Corporation, Armonk, NY). Results: Of the 309 live-born neonates (in utero demise of one Mo Di twin), 28% were Mo Di twins. Thirty-three percent of both Mo Di and Di Di twins did not require admission to the NICU. Two sets of Mo Di twins had twin-to-twin transfusion syndrome (TTTS) and required laser therapy antenatally. Mo Di twins admitted to the NICU were younger (mean age 31 weeks) and lighter in weight (mean weight 1627g) than Di Di twins (mean age 32 weeks, mean weight 1955g) admitted to the NICU. Mo Di twins had a mean length of stay (LOS) in the NICU of 44 days versus 39 days for Di Di twins (p 0.007). Mo Di twins also had a higher need for respiratory support than Di Di twins (p 0.002). Linear regression revealed longer LOS in the NICU was associated with Mo Di gestation (p 0.003), less than 30 weeks’ gestation at birth (p 0.000), birth weight less than 1500g (p 0.000), receipt of tocolytics (p 0.029), receipt of at least 2 doses of antenatal betamethasone (p 0.007), and premature prelabor rupture of membranes (PPROM) (p 0.030). Labor before birth (p 0.033) was associated with decreased LOS. Linear regression analysis revealed that longer duration of respiratory support was associated with Mo Di gestation (p 0.006), less than 30 weeks’ gestation at birth (p 0.000), birth weight less than 1500g (p 0.000), and maternal diabetes (p 0.046). Need for admission to NICU, survival, BPD, intraventricular hemorrhage (IVH), and spontaneous intestinal perforation (SIP) were not significantly different between the groups. There were no cases of necrotizing enterocolitis (NEC), and no neonates required placement of a tracheostomy in either group. One infant in the Mo Di group required gastrostomy tube placement. Genetic anomalies were diagnosed in Mo Di twins (Williams syndrome 1, Waardenburg syndrome 2). No major anomalies were found in the Di Di twins. Birth defects in Mo Di twins included Hirschsprung’s disease (n=1), coronary artery fistula (n=1), and solitary kidney (n=1). One neonate had a constellation of cleft palate, vascular ring, and left hypoplastic lung. Discussion: Our study found that Mo Di twins admitted to the NICU were younger and lighter compared to Di Di twins admitted to the NICU. Mo Di twins had longer NICU stays and required respiratory support for longer than Di Di twins. While additional studies need to be performed to evaluate long-term outcomes of twins based on chorionicity and the effects of maternal conditions on short-term outcomes, the common belief that Mo Di twins have worse short-term outcomes as compared to Di Di twins is true in regard to length of NICU stay and length of respiratory support.