Perinatal Death in Triplets by Gestational Age: A Retrospective Cohort from Two Tertiary Hospitals

This study aimed to describe a contemporary cohort of triplet pregnancies from two tertiary centers in a middle-income country and evaluate the association between gestational age (GA) at birth and perinatal death. We developed and internally validated a GA-based risk model.

Retrospective cohort from two tertiary hospitals (2015-2024). The unit of analysis was the fetus/neonate, with cluster-robust standard errors at the mother level. Primary outcome: Perinatal death (stillbirth ≥23^0/7 weeks or neonatal death ≤28 days). GA was modeled with logistic regression using restricted cubic splines; Firth penalization addressed separation where applicable. Internal validation used 200 bootstrap resamples.

The cohort included 150 neonates; perinatal death occurred in 23 (15.4%). Median GA was 33 (31-34) weeks overall, 34.0 (32.0-34.0) in survivors, and 25.0 (24.0-28.0) in perinatal deaths. In the adjusted spline model, GA was the dominant predictor (overall Wald χ² = 1,473.66, df = 3, p < 0.001; non-linearity χ² = 424.92, df = 2, p < 0.001), while severe preeclampsia was not significant (χ² = 0.10, p = 0.750). The category-based Firth model showed markedly elevated odds of perinatal death at earlier gestations versus ≥34 weeks: <28 weeks; adjusted odds ratio (aOR) = 871.15 (95% confidence interval [CI]: 81.25-124,006.80, p < 0.001); 28 to <32 weeks, aOR = 50.22 (5.45-6,682.53, p < 0.001); 32 to <34 weeks, aOR = 5.34 (0.26-804.14, p = 0.278); and severe preeclampsia, aOR = 1.02 (0.09-7.17, p = 0.984). The internally validated model demonstrated excellent discrimination (optimism-corrected area under the receiver operating characteristic curve [AUROC], 0.972) and good overall performance (Brier score, 0.047), with a calibration intercept of -0.129, a slope of 0.696, and a maximum absolute calibration error (E _max) of 0.104.

In triplet pregnancies, GA at birth is the dominant determinant of perinatal death, with a steep risk gradient at earlier gestations. A GA-based model demonstrates excellent discrimination and acceptable calibration following bootstrap internal validation, supporting its use in informing counseling and timing-of-delivery decisions in this high-risk population.

· Perinatal mortality in triplet pregnancies decreases sharply after 32 weeks.. · Most perinatal deaths occur before 32 weeks of gestation.. · These findings support delivery planning around 32 to 33 weeks.. · Data from low- and middle-income countries' settings provide guidance for counseling and NICU planning.. · A simple GA-only model showed excellent discrimination (area under the curve = 0.97)..