Stillbirths and live births in the periviable period.

<bold>Purpose: </bold>We use data from California, where 13% of US births occur, to address two questions arising from efforts in the first decade of this century to avoid stillbirths before 25 6/7 weeks of gestation (i.e., in the periviable period). First, did stillbirths decline in the first decade of this century? Second, if stillbirths did decline, did periviable live births increase simultaneously? Answering these questions is important given that periviable infants represent less than 1% of live births but account for roughly 40% of infant mortality and 20% of hospital-based obstetric costs in the United States.<bold>Methods: </bold>We constructed 240 monthly conception cohorts, starting with that conceived in January 1991, from 9,880,536 singleton pregnancies that reached the 20 0/7 week of gestation. We used time-series design and Box-Jenkins methods that address confounding by autocorrelation, including secular trends and seasonality to answer our questions.<bold>Results: </bold>We detected a downward shift in stillbirths in April 2007 that coincided with an upward shift in periviable live births.<bold>Conclusions: </bold>Our findings imply that, since 2007, fewer Californians than expected from history and from the size of conception cohorts reaching 20 0/7 weeks of gestation have had to contend with the sequelae of stillbirths, but more than expected likely have had to contend with those of periviable births. [ABSTRACT FROM AUTHOR]