# Interpregnancy Interval and Pregnancy Outcomes

> **NIH NIH R03** · RESEARCH INST NATIONWIDE CHILDREN'S HOSP · 2020 · $76,967

## Abstract

PROJECT SUMMARY-ABSTRACT
It is believed that women who become pregnant again shortly after giving birth are at elevated risk of
having a preterm infant in the subsequent pregnancy. The World Health Organization states: “After a
live birth, the recommended interval before attempting the next pregnancy is at least 24 months in order
to reduce the risk of adverse maternal, perinatal and infant outcomes.” The American Congress of
Obstetricians and Gynecologists states “The optimal interval between delivery and subsequent
pregnancy is 18 months to 5 years; the greatest risk of low birth weight and preterm birth occurs when
the interconception interval is less than 6 months.” Recently, novel evidence has questioned short
intervals’ causality for preterm birth. Studies in Australia, California, Canada and Sweden used case-
crossover designs, comparing preterm birth following short versus longer intervals within women who
had 3 livebirths, and therefore 2 intervals, answering the question “is risk of preterm birth after a short
interval greater than that of the same woman after a longer interval?” Two studies found intervals <6
months not to carry increased risk, and two found slight increases for short intervals, although the risk
was less than was observed in a corresponding conventional analysis. However, experts have raised
concerns regarding the case-crossover design for this question. Because of these concerns, a critical
need exists to assess the causality the association of short interpregnancy interval and preterm birth, so
that existing recommendations can be either reaffirmed or modified. Our long term goal is to understand
the etiology of preterm birth, and learn how it may be prevented. Our objective in this application is to
establish the most appropriate way to evaluate the impact of interpregnancy interval on preterm birth;
and explore the impact of study design on this question utilizing detailed data collected by the National
Survey of Family Growth. We will employ modern causal inference methods to compare results of a
conventional analysis; an analysis utilizing the enhanced NSFG data, including the degree of
pregnancy intendedness and how long the first child was breastfed; and several within-woman
crossover analyses. We propose 2 aims: 1)To determine whether after adjustment for enhanced time-
varying confounders, women who become pregnant shortly after a birth are at increased risk of
preterm delivery. 2) To describe the effects of study design, compare the properties of different
designs, and determine the optimal design for the association of interval and preterm birth. Upon
completion of this project we expect to have provided important data to inform official
recommendations regarding pregnancy spacing, thereby influencing clinical care and policy, and
improving maternal and neonatal health.

## Key facts

- **NIH application ID:** 9991877
- **Project number:** 5R03HD099241-02
- **Recipient organization:** RESEARCH INST NATIONWIDE CHILDREN'S HOSP
- **Principal Investigator:** Mark A Klebanoff
- **Activity code:** R03 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $76,967
- **Award type:** 5
- **Project period:** 2019-08-12 → 2021-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9991877

## Citation

> US National Institutes of Health, RePORTER application 9991877, Interpregnancy Interval and Pregnancy Outcomes (5R03HD099241-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9991877. Licensed CC0.

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