Late preterm birth: appreciable risks, rising incidence.

p e l s a t p p a d t h w t m r c r c n t a n v c H t t t u t a estern countries have experienced a sharp rise in the occurrence of preterm birth in recent decades. The reasons for this rise are well ocumented and include more frequent obstetric intervenion (particularly induction of labor), a higher rate of winning, mostly because of the use of ovulation stimulaion and assisted reproductive techniques with multiple mbryo transfer, and delayed childbearing, because older others, even those who deliver singletons, are at increased isk of preterm birth. The recent rise in preterm birth has occurred throughut the industrialized world, but has been particularly marked n the United States. Part of the reason that the United tates has such a high incidence of preterm birth is the xtremely high rate among African-Americans. Another, less ell-appreciated reason is that US preterm birth statistics, nlike those of most other high-income countries, are based n menstrual-based gestational age estimates, rather than ltrasound scanning estimates. All states except California lso record a clinical estimate of gestational age, which (at east until recently) did not specify the basis for the estimate. he clinical estimate provides rates of preterm birth that are ore similar to, albeit still somewhat higher than, those of ther industrialized countries. Finally, the high incidence of reterm birth in the United States, even among Caucasian others, is certainly at least partly caused by higher rates of bstetric intervention in general and labor induction in paricular. More frequent obstetric intervention in the United tates compared with other high-income countries may be elated to the medico-legal climate, closer fetal surveillance, nd the wish to avoid potentially avoidable obstetric disasters, articularly stillbirth. Most of the increase in preterm birth in the United tates and elsewhere is attributable to increases in late preerm birth, primarily between 34 and 36 weeks of gestation. dvances in neonatal care, including intensive care, have arkedly improved survival throughout the preterm gestaional age range. But these advances may have led many bstetricians and neonatologists to consider late preterm irths to be risk-free. Although the absolute risks are exremely low in such infants, my colleagues and I have shown hat even 34to 36-week infants are at increased risk for ortality in both the neonatal and post-neonatal periods. he relative risks (versus infants born at term) are modest ompared with infants born at 32 weeks, but the much arger and increasing numbers of births at late preterm gesl