Patterns of recurrent preterm birth in Western Australia: A 36-year state-wide population-based study

BACKGROUND

It is known that a previous preterm birth increases the risk of a subsequent preterm birth, but a limited number of studies have examined this beyond two consecutive pregnancies.

AIMS

This study aimed to assess the risk and patterns of (recurrent) preterm birth up to the fourth pregnancy.

MATERIALS AND METHODS

We used Western Australian routinely linked population health datasets to identify women who had two or more consecutive singleton births (≥20 weeks gestation) from 1980 to 2015. A log-binomial model was used to calculate risk ratios (RRs) and 95% confidence interval (CIs) for preterm birth risk in the third and fourth deliveries by the combined outcomes of previous pregnancies.

RESULTS

We analysed 255 435 women with 651 726 births. About 7% of women had a preterm birth in the first delivery, and the rate of continuous preterm birth recurrence was 22.9% (second), 44.9% (third) and 58.5% (fourth) deliveries. The risk of preterm birth at the third delivery was highest for women with two prior indicated preterm births (RR 12.5, 95% CI: 11.3, 13.9) and for those whose first pregnancy was 32-36 weeks gestation, and second pregnancy was less than 32 weeks gestation (RR 11.8, 95% CI: 10.3, 13.5). There were similar findings for the second and fourth deliveries.

CONCLUSIONS

Our findings demonstrate that women with any prior preterm birth were at greater risk of preterm birth in subsequent pregnancies compared with women with only term births, and the risk increased with shorter gestational length, and the number of previous preterm deliveries, especially sequential ones.

Trends in provider-initiated versus spontaneous preterm deliveries, 2004-2013

OBJECTIVE

The objectives of this study were as follows: (i) to estimate the proportion of preterm deliveries at a tertiary perinatal center that were provider-initiated versus spontaneous before and after a 2009 policy to reduce elective early-term deliveries, and (ii)to evaluate whether shifts in type of preterm delivery varied by race/ethnicity.

METHOD

We performed a retrospective cohort study of preterm deliveries over a 10-year period, 2004 to 2013, including detailed review of 929 of 5566 preterm deliveries, to designate each delivery as provider-initiated or spontaneous. We dichotomized the time period into early (2004 to 2009) and late (2010 to 2013). We used log-binomial regression to calculate adjusted risk ratios.

RESULT

Of the 46 981 deliveries, 5566 (11.8%) were preterm, with a significant reduction in the overall incidence of preterm delivery from 12.3 to 11.2% (P=0.0003). Among the 929 preterm deliveries analyzed, there was a reduction in the proportion of provider-initiated deliveries from 48.3 to 41.8% that was not statistically significant. The proportion of provider-initiated preterm deliveries among Black, but not White, women declined from 50.8 to 39.7% (adjusted relative risk: 0.66; 95% confidence interval (CI): 0.45 to 0.97). This coincided with a larger reduction in overall preterm deliveries among Black women (16.2 to 12.8%) vs White women (12.3 to 11.2%) (P interaction=0.038). By 2013, the incidence of preterm deliveries had decreased for both Black (12.1%) and White women (11.4%), and the difference was no longer statistically significant (P=0.7).

CONCLUSION

We found a reduction in preterm deliveries after a policy targeted at reducing elective early-term deliveries in 2009 that coincided with reductions in the proportion of provider-initiated preterm deliveries, especially among Black women.