Smaller placentas and maternal vascular malperfusion are associated with worse pregnancy outcomes in triplet...

This study aimed to compare placental pathological findings and the prevalence of maternal, fetal, obstetric, and perinatal outcomes in triplet pregnancies based on chorionicity.

This single-center, retrospective, observational case-control study included all triplet pregnancies followed in a tertiary referral hospital between 2000 and 2024 with available placental pathological examination. Univariate statistical analyses were performed.

A total of 111 triplet pregnancies were analyzed: 56 without a monochorionic (MC) component and 55 with a MC component. Maternal baseline characteristics were similar between groups. Fetal complications were significantly more frequent in the group with a MC component, including twin-twin transfusion syndrome (p = 0.02; odds ratio [OR] = 0.44; 95 % confidence interval [CI] 0.35-0.55), fetal growth restriction (FGR) (p = 0.03; OR = 2.05; CI 1.08-3.88), and intrauterine fetal demise (IFD) (p = 0.01; OR = 2.16; CI 1.16-4.01). Neonatal birth weight <1500 g was also more frequent in the group with a MC component (p = 0.02; OR = 3.23; CI 1.51-6.92). The smallest placentas were observed in the group with a MC component (p < 0.01). Histopathologically, placentas with a MC component showed higher rates of accelerated villous maturation (p < 0.01; OR = 3.57; CI 1.88-6.77) and distal villous hypoplasia (p = 0.01; OR = 2.00; CI 1.15-3.46).

Our findings suggest that triplet pregnancies with a MC component are associated with worse pregnancy outcomes, including increased rates of FGR, IFD, prematurity, and low neonatal birth weight. Triplet pregnancies with a MC also showed smaller placentas and a higher frequency of maternal vascular malperfusion lesions. The increased morbidity observed in triplet pregnancies with a MC component may reflect underlying physiological alterations that are visible in gross and histopathological placental features.