The "Late Preterm" Birth-Ten Years Later.

Abstract

* Abbreviations: ACOG — : American Congress of Obstetricians and Gynecologists NCHS — : National Center for Health Statistics NICHD — : Eunice Kennedy Shriver National Institute of Child Health and Human Development SMFM — : Society for Maternal and Fetal Medicine It is now 10 years since the phrase late preterm entered the medical lexicon.1 The impact of this milestone on perinatal patient care and research and a brief note concerning the unresolved issues on this topic are the focus of this Pediatric Perspective. In 1969, the World Health Organization proposed that a preterm birth should be defined as “childbirth occurring at less than 37 completed weeks, or 259 days of gestation counting from the first day of the last menstrual period in women with regular (28-day) menstrual cycles.”2 However, in the mid-1970s through the 1980s, researchers began identifying their research participants close to term gestation as “near-term.” Although no specific lower gestational age limits were stated, the implication was that such participants were fully mature and did not differ from full-term infants in any respect.3 Coincidentally, the US preterm birth rate, calculated from the last menstrual period, increased 31% between 1981 and 2003 (9.4% in 1981 and 12.3% in 2003).4 Most of this increase was due to births between 32 and 36 weeks. The distribution of gestational age at delivery had shifted toward lower gestational ages, such that in 2002 the peak gestational age for US singleton births was 39 weeks, compared with 40 weeks in 1991. During this period, for pregnancies between 32 and 36 weeks, there was a 22% increase in medical interventions, defined as inductions or cesarean births in the absence of prolonged rupture of the membranes.4 Thus, at the turn of the 21st century, some startling perinatal epidemiologic data had emerged. There was a steady increase in US preterm births. The fastest-growing segment was births between 34 and 36 weeks’ gestation, accounting for 74% of preterm births. The ethnic and racial … Address for correspondence to Tonse N. K. Raju, MD, DCH, 6710-B Rockledge Blvd, Room 2330, Mail Stop 7002, Bethesda, MD 20892. E-mail: rajut{at}mail.nih.gov