Routine ultrasound examination at 41 weeks of gestation and risk of post-term severe adverse fetal outcome: a retrospective evaluation of two units, within the same hospital, with different guidelines.

OBJECTIVE

To study whether a routine with a routine ultrasound examination (routine scan) at 41 gestational weeks as compared with ultrasound on clinical indication (indicated scan), lowered the risk of severe adverse fetal outcome in post-term period.

DESIGN

A retrospective cohort study.

SETTING

Karolinska University Hospital, Stockholm, Sweden.

POPULATION

Eight years of deliveries, 2002-2009.

METHOD

One of the two delivery units at Karolinska University Hospital used a routine scan at 41 week of gestation and the other unit used an indicated scan. Severe adverse fetal outcome were defined: severe asphyxia, death or cerebral damage. The study was analysed using logistic regression with adjustment for potential confounders.

MAIN OUTCOME MEASURES

Differences in post-term severe adverse fetal outcome.

RESULTS

No increased risk of post-term severe adverse fetal outcome was seen at the unit using a routine scan; conversely, a 48% significantly increased risk was seen at the unit using an indicated scan (OR 0.89, 95% confidence interval, CI, 0.5-1.5 and OR 1.48, 95% CI 1.06-2.1, respectively). Comparing post-term periods, there was no significantly increased risk at the unit using indicated scans (OR 1.6, 95% CI 0.9-3.0). There was a 60% increased prevalence of small-for-gestational age (SGA) newborns in the post-term period at the unit using indicated scans (OR 1.6, 95% CI 1.1-2.4), but no differences in operative delivery.

CONCLUSION

A policy to use routine scans at 41 weeks of gestation seems to normalise an increased post-term risk of severe adverse fetal outcome, possible due to increased awareness of SGA and/or oligohydramniosis.