1998; Erickson and Bjerkedal, 1978; Ferraz et al., 1988; Fuentes-Afflick and Hessol, 2000; Hsieh et al., 2005; Kallan, 1992, 1997; Klebanoff, 1988; Lang et al., 1990; Miller, 1994; Rawlings et al., 1995; Shults et al., 1999; Smith et al., 2003; Zhu and Le, 2003; Zhu et al., 2001). These published reports did not distinguish spontaneous from indicated preterm birth, however. The definition of short interpregnancy interval varies widely across studies; the most common definition is less than or equal to 6 months.
The relationships between short interpregnancy interval and preterm birth, low birth weight, and small-for-gestational age birth have been noted to be similar in magnitude and significance for African American and white women (James et al., 1999; Kallan, 1992, 1997; Zhu et al., 2001). Most studies have found that the prevalence of short interpregnancy intervals is higher among African American women than white women (James et al., 1999; Kallan, 1992, 1997; Zhu et al., 2001), but others have not found such a higher prevalence (Kallan, 1992; Klerman et al., 1998). International studies have shown that a short interpregnancy interval has been associated with preterm birth in rural Greece, the Philippines, the United Arab Emirates, and Latin America (Blackmore-Prince et al., 2000; Conde-Agudelo et al., 2005; Lang et al., 1990; Zhu et al., 2001).
The magnitude of the increased risk for preterm birth with an interpregnancy interval of less than 6 months is estimated to be 30 to 60 percent (Kallan, 1997). A single report has suggested that the magnitude and the significance of a short interpregnancy interval are the greatest when the index pregnancy was a preterm birth rather than a term birth (Hsieh et al., 2005).
Klebanoff (1988) notes that a short interpregnancy interval is primarily a marker for a woman who is otherwise at high risk of delivering her infant preterm and that modification of that interval alone may be unlikely to have a major impact on low birth weight. Other investigators also support the notion that a short interpregnancy interval may function as a marker of other risk factors rather than exerting an independent effect on preterm birth (Brody and Braken, 1987; Erickson and Bjerkedal, 1978). This concept may be extended to the impact of a short interpregnancy interval on low birth weight. In a Brazilian study, the effect of a short interpregnancy