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TOPLINE:

The duration of membrane rupture and number of vaginal examinations significantly influenced early gut microbiome colonization in vaginally born twins.

METHODOLOGY:

• Researchers investigated intrapartum events during vaginal twin births — specifically the duration of membrane rupture and the number of vaginal examinations — as factors affecting early gut microbiome colonization patterns between first and second twins.
• This prospective longitudinal cohort study was conducted between February 2021 and January 2024 at a tertiary referral centre and enrolled 20 women with twin pregnancies ≥ 36 weeks (40 infants requiring identical care) undergoing vaginal birth.
• The gestational age at birth was 37.07 (36.75-37.57) weeks. Maternal age was 36.50 (30.00-38.75) years, and BMI was 25.48 (23.46-27.62). Paired stool samples were collected on days 4 and 28 postnatally.
• Gut microbiome was analysed via 16S rDNA sequencing. Microbial diversity was determined by calculating the Shannon-Weaver diversity index and the Bray-Curtis beta diversity index.
• The primary outcome of the study was to evaluate the impact of membrane rupture and vaginal examinations on the infant gut microbiome. Secondary outcomes included infection rates, dermatologic diagnoses, and infant growth metrics over the follow-up period.

TAKEAWAY:

• First twins had significantly more vaginal examinations (median, 5.50; interquartile range [IQR], 4.00-7.25 vs median, 1.00; IQR, 1.00-1.00; P < .001) and had a longer interval from membrane rupture to birth (median, 524 min; IQR, 324-734.5 vs median, 7.5 min; IQR, 4.5-9.0; P < .001) than second twins.
• On day 4, the abundance of Bifidobacterium spp. was > 50% in first twins vs < 25% in second twins. Bifidobacterium longum was the dominant species in 20-40% of the samples and was more abundant in first twins than in second twins.
• By day 28, 75% of samples showed similar Bifidobacterium profiles between twins, indicating microbiome homogenization (Shannon index: mean, 0.520; 95% CI, 0.427-0.614 vs mean, 0.614; 95% CI, 0.526-0.703; P = .646).
• During the 25.5-month follow-up, no significant differences were observed in growth (weight percentile: median, 65.50; IQR, 45.03-70.85 vs median, 65.50; IQR, 48.03-77.88; P = .881) or infection rates (10% vs 20%; P = .661).

IN PRACTICE:

"[In] twins who share the same environment and mother, not all vaginal births are equal. Although the gut microbiome appears to progressively homogenize when similar nurturing and environmental conditions are met, clear differences exist in the early days of life," the authors wrote.

SOURCE:

The study was led by Marcos Javier Cuerva, Department of Obstetrics, Hospital Universitario La Paz, Paseo La Castellana, Spain, Madrid. It was published online on July 30, 2025, in European Journal of Pediatrics.

LIMITATIONS:

The study was limited by the absence of maternal vaginal sample analysis, which prevented the assessment of birth order effects on maternal microbiota, and an insufficient sample size to robustly evaluate perinatal confounders such as intrapartum antibiotic exposure or feeding practices, as these factors were inherently controlled equally in the twin design.

DISCLOSURES:

This study was supported by The Health Institute Carlos III. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.