Smaller placentas and maternal vascular malperfusion are associated with worse pregnancy outcomes in triplet pregnancies with a monochorionic component.

INTRODUCTION

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

METHODS

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.

RESULTS

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).

DISCUSSION: 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.