Uterine surgery before a first birth tracks with later preterm birth and stillbirth

Design

population-based record linkage, retrospective

Population

520,050 women with a first birth in New South Wales, Australia, 2007-2019

Primary outcome

preterm birth and stillbirth after uterine surgery preceding the first birth

Effect

preterm birth adjusted OR 1.51 (95% CI 1.47-1.55); stillbirth adjusted OR 1.39 (95% CI 1.26-1.53)

A population-linked study covered every first birth in New South Wales between 2007 and 2019 - 520,050 women - and matched them against 99,659 uterine surgical procedures recorded from 2001 onwards. Uterine surgery before the first birth had occurred in 14.7% of the cohort. After adjustment, it was associated with preterm birth (adjusted odds ratio 1.51, 95% CI 1.47-1.55) and with stillbirth (adjusted odds ratio 1.39, 95% CI 1.26-1.53). The association strengthened with repeated procedures and was largest at the earliest gestational ages.

The proposed mechanisms are old ones: cervical dilatation weakening the cervix, and endometrial scarring impairing later placentation. What is new is the scale of the denominator, which is large enough to separate preterm birth at 28 weeks from preterm birth at 36. The authors call it hypothesis-generating, and the honest reading is that confounding by indication has not been excluded - a woman having repeated uterine instrumentation for subfertility or recurrent early pregnancy loss already carries obstetric risk before anyone touches her cervix.

What it changes is the conversation before a procedure rather than the procedure itself. Diagnostic hysteroscopy, polypectomy and dilatation and curettage for incomplete miscarriage are common in Indian practice, often in women who have not yet had a child, and medical alternatives exist for several of the indications. This argues for asking whether the surgery is needed now, and for noting it in the antenatal record when the woman later books.

• Ask about previous uterine instrumentation at booking, including procedures done elsewhere and for early pregnancy loss
• Record the number of procedures, not just whether there was one - risk rose with repetition
• Where medical management of incomplete miscarriage is appropriate, weigh it against instrumentation in a nulliparous woman
• Consider a cervical length assessment in the second trimester where prior surgery involved cervical dilatation
• Do not counsel this as a causal risk - the indication for surgery may be doing some of the work

Why it matters

It turns a routine gynaecological procedure in a nulliparous woman into a decision with an obstetric consequence years later.

Don't overread it

This was observational and the reason for the surgery may itself raise pregnancy risk - it does not show that avoiding surgery prevents preterm birth.

The statistics, in plain English

An adjusted odds ratio of 1.51 with a confidence interval of 1.47-1.55 is a precise estimate, but precision comes from half a million births rather than from good control of confounding - a narrow interval says the association is real in this dataset, not that surgery caused it. Absolute risk matters more than the ratio here: on a baseline stillbirth risk of roughly 0.5%, an odds ratio of 1.39 moves it to about 0.7%, which is a real but small shift for an individual woman.

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