Preterm rupture of membranes is four conditions wearing one name

Design

single-institution prospective cohort study with transabdominal amniocentesis at admission, amniotic fluid interleukin-6 and culture plus molecular microbiology

Population

961 singleton pregnancies with preterm prelabour rupture of membranes between 23+0 and 36+6 weeks

Primary outcome

gestational-age distribution of the four intra-amniotic categories, microbial profiles, and short-term perinatal and neonatal outcomes

Effect

early-onset neonatal sepsis 12% / 4% / 5% / 2% across infection, sterile inflammation, microbial invasion alone and negative (P < 0.0001); infection adjusted OR 3.4 (95% CI 1.7-7.0)

This single-institution cohort took 961 singleton pregnancies with preterm prelabour rupture of membranes between 23+0 and 36+6 weeks, all of whom had transabdominal amniocentesis at admission, and sorted them by two axes: intra-amniotic inflammation, measured by amniotic fluid interleukin-6, and microbial invasion, detected by culture and molecular methods.

The four resulting groups were unevenly sized and very unevenly dangerous. Intra-amniotic infection — both inflammation and microbes — accounted for 17%; sterile inflammation for 7%; microbial invasion without inflammation for 11%; and 65% had neither. Early-onset neonatal sepsis followed the same order: 12%, 4%, 5% and 2% (P < 0.0001). After adjustment, intra-amniotic infection carried 3.4 times the odds of early-onset sepsis (95% CI 1.7 to 7.0) and twice the odds of a serious composite adverse perinatal outcome (95% CI 1.1 to 3.4). Of 64 microbial species found, Ureaplasma accounted for nearly two-thirds of detections — and among pregnancies with microbial invasion, organisms other than Ureaplasma did worse.

The feasibility data are as important as the biology: amniocentesis yielded fluid in 98% of attempted procedures and 93% of eligible pregnancies. So this is a categorisation you could actually apply, in a unit with the assay and the skill. Two-thirds of women with preterm rupture had neither infection nor inflammation and a 2% sepsis rate — a group currently managed with the same anxiety as the 17% who have a 12% rate. Whether acting on the category improves outcomes has not been tested; this is a single centre and an observational description.

• Recognise that most preterm prelabour rupture has neither infection nor inflammation — a 2% early-onset sepsis rate
• Where amniocentesis and amniotic fluid interleukin-6 are available, the four categories are identifiable in practice
• Treat a non-Ureaplasma organism in amniotic fluid as the higher-risk finding
• Sterile inflammation is not benign but sits well below intra-amniotic infection on risk
• No trial has yet shown that managing by category improves outcomes — this describes risk, it does not validate a protocol

The statistics, in plain English

An adjusted odds ratio of 3.4 with an interval from 1.7 to 7.0 is a clear signal, though the width reflects only 19 sepsis cases in the infection group — small event counts always give loose estimates. The unadjusted percentages (12% vs 2%) are more directly useful for counselling than the odds ratios, because odds overstate risk when outcomes are uncommon in one group and not another. This is one institution with a specific amniocentesis practice, so both the category distribution and the sepsis rates may differ elsewhere.

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