Uterine surgery before a first birth, and what follows it

Design

Population-based record-linkage cohort study

Population

520,050 women with a first birth in New South Wales, 2007 to 2019; 99,659 uterine procedures

Primary outcome

Preterm birth and stillbirth in the first pregnancy after surgery

Effect

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

All 520,050 first births in New South Wales between 2007 and 2019 were linked to hospital records covering 99,659 uterine procedures. Uterine surgery before the first birth had occurred in 14.7 per cent of the cohort and was associated with later preterm birth (adjusted odds ratio 1.51) and stillbirth (adjusted odds ratio 1.39). The association strengthened with repeated procedures and was strongest at the earliest gestations.

The mechanism proposed is mechanical and plausible: cervical dilatation weakening the cervix, endometrial scarring impairing later placentation. The study cannot show it. Confounding by indication is the obvious rival explanation — a woman having a hysteroscopy for recurrent miscarriage or a retained conception already carries risk that has nothing to do with the instrument.

What it should change is the conversation before an elective procedure in a woman who has not yet had a child. Polypectomy for a small asymptomatic polyp, a diagnostic D and C where imaging would do, a repeat evacuation on soft grounds — these are the decisions this paper touches, not the emergency ones.

• Ask whether the procedure could be replaced by imaging or by expectant management before listing it.
• Count previous procedures in the antenatal history; the association rose with number.
• Consider cervical length surveillance in a later pregnancy where dilatation was repeated.
• Do not convert this into a reason to avoid necessary surgery; the indications themselves carry risk.
• Record the type of procedure, not just 'uterine surgery' — dilatation and non-dilatation procedures were not equivalent.

Why it matters

It puts a later obstetric cost on a decision usually weighed only against its immediate gynaecological benefit.

Don't overread it

This is observational and cannot show that the surgery itself causes the preterm birth.

The statistics, in plain English

The confidence intervals are tight (1.47 to 1.55 for preterm birth) because half a million births contribute, which tells you the association is precisely estimated, not that it is causal. Precision and validity are different things: an adjusted odds ratio from linked administrative data can be extremely precise and still reflect the reason for surgery rather than the surgery. The authors call it hypothesis-generating, and that is the right label.

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