Unintended pregnancy and interpregnancy interval by maternal age, National Survey of Family Growth

Abstract

Background: The relationship between unintended pregnancy and interpregnancy interval (IPI) across maternal age is not clear.

Methods: Using data from the National Survey of Family Growth, we estimated the percentages of pregnancies that were unintended among IPI groups (<6, 6-11, 12-17, 18-23, 24+ months) by maternal age at last live birth (15-19, 20-24, 25-29, 30-44 years).

Results: Approximately 40% of pregnancies were unintended and 36% followed an IPI<18 months. Within each maternal age group, the percentage of pregnancies that were unintended decreased as IPI increased.

Conclusion: Unintended pregnancies are associated with shorter IPI across the reproductive age spectrum.

Keywords: Birth spacing; Interpregnancy intervals; Postpartum contraception; Pregnancy intention.

Fig. 1.

A) The percentage of pregnancies unintended (unwanted or mistimed) and B) the percentage of pregnancies conceived within a short (<18 month) interpregnancy interval by maternal age (in years) at last live birth: NSFG 2006–2010, 2011–2015 (6382 pregnancies among 5079 women). Linear trends were assessed using logistic models with age category at last live birth (15–19, 20–24, 25–29, 30–44 years) as a continuous variable.

Fig. 2.

The percentage of pregnancies unintended (unwanted or mistimed) by interpregnancy interval since last live birth, by maternal age at time of last live birth: NSFG 2006–2010, 2011–2015. Prevalence ratio (PR) and 95% confidence interval for unintended pregnancy are in comparison to reference group 18–23 months (6382 pregnancies among 5079 women). Linear trends were assessed using logistic models with interpregnancy interval (0–5, 6–11, 12–17, 18–23, 24+ months) as a continuous variable.