Severe maternal morbidity is a composite variable that includes adverse maternal outcomes during pregnancy that are associated with maternal mortality. Previous literature has shown that interpregnancy interval is associated with preterm birth, fetal growth restriction, and low birthweight, but the association of interpregnancy interval and composite severe maternal morbidity is not well studied.

We sought to determine the relationship between interpregnancy interval (stratified as <6, 6–11, 12–17, 18–23, 24–59, and ≥60 months) and severe maternal morbidity, which we considered both with and without blood transfusion.

This was a retrospective cohort study of multiparous women 15 to 54 years old with singleton, nonanomalous births between 23 and 42 weeks gestation in California (2007–2012). We defined severe maternal morbidity as the composite score of a published list of the International Classification of Diseases, ninth Revision, diagnoses and procedure codes, provided by the Centers for Disease Control and Prevention. We used chi-square tests for categorical variables, and multivariable logistic regression models were used to determine the association of interpregnancy interval (independent variable) with severe maternal morbidity (dependent variable), adjusted for maternal race and ethnicity, age, education, body mass index, insurance, prenatal care, smoking status, and maternal comorbidity index score.

Here, 1,669,912 women met the inclusion criteria, and of these women, 14,529 (0.87%) had severe maternal morbidity and 4712 (0.28%) had nontransfusion severe maternal morbidity. Multivariable logistic regression models showed that compared with women with 18 to 23 months interpregnancy interval, women with an interpregnancy interval of <6 months (adjusted odds ratio, 1.23; 95% confidence interval, 1.14–1.34) and ≥60 months (adjusted odds ratio, 1.11; 95% confidence interval, 1.04–1.19) had significantly higher adjusted odds of severe maternal morbidity. The odds of nontransfusion severe maternal morbidity is higher in women with long interpregnancy intervals (≥60 months) after controlling for the same potential confounders (adjusted odds ratio, 1.17, 95% confidence interval, 1.04–1.31). In addition, we found significantly higher odds of requiring ventilation (adjusted odds ratio, 1.34; 95% confidence interval, 1.03–1.75) and maternal sepsis (adjusted odds ratio, 2.08; 95% confidence interval, 1.31–3.31) in women with long interpregnancy interval.

The risk of severe maternal morbidity was higher in women with short interpregnancy interval (<6 months) and long interpregnancy interval (≥60 months) compared with women with normal interpregnancy interval (18–23 months). The risk of nontransfusion severe maternal morbidity was significantly higher in women with long interpregnancy interval (≥60 months). Interpregnancy interval is a modifiable risk factor, and counseling women to have an adequate gap between pregnancies may be an important strategy to decrease the risk of severe maternal morbidity.