Premature infants

Premature infants are babies born before full-term gestation. Prematurity is an important topic in both pediatrics and obstetrics because the health of a baby at birth is strongly dependent on completion of a term pregnancy. Premature babies account for a disproportionately high amount of neonatal morbidity and mortality of all babies, that is, when epidemiologic statistics on reported illness and deaths among newborns are compiled, premature infants are overrepresented among newborns.

Prematurity is qualitatively different according to the extent of in utero (in the womb) development that the baby has undergone, the closer that the baby is to term, generally, the better his or her chances of survival and a normal life after survival.The "youngest" of premature newborns, those who have undergone the least amount of time in the womb, are generally worse off than the infants who have come closer to term gestation. Most of the severe problems associated with prematurity, that is, death, disability, and illness, affects “very preterm” infants (those born before 32 weeks' gestation), and especially “extremely preterm” infants (those born before 28 weeks of gestation). (Tucker J. McGuire W. Epidemiology of preterm birth.[see comment]. [Review] [0 refs] [Journal Article. Review] BMJ. 329(7467):675-8, 2004 Sep 18. UI: 15374920). About 1-2% of babies in Europe and North America are "very preterm". There are other characteristics that are important in physicians' view of the health and care of these babies, but, as in all populations defined by medical criteria, the specific way that this term is applied is important in reviewing the known literature on prematurity. Just how is prematurity defined?

Prediction of due date and estimation of gestational age

A fair percentage of babies who are pre-term by estimation of a calendar due date have characteristics of full term babies. One study 3 comparing sonographic with menstrual dates from a large database found that only 78% of pregnancies designated preterm (less than 37 completed weeks) by menstrual dates were actually preterm, according to a confirming sonogram. (Klebanoff MA. Gestational age: not always what it seems.[comment]. [Comment. Editorial] Obstetrics & Gynecology. 109(4):798-9, 2007 Apr. UI: 17400838). That de date is determined by the reported date of the last menstrual period, and in women who do not keep records, and for those who have irregular periods, the date given may be inaccurate.

In the embryo and fetus, development proceeds in a predictable fashion. In general, in all vertebrate embryos, stages occur first at the head, and later the "tail", and first towards the midline and later at the distal areas of the body. There are changes in the fetal physiology as the gestational age increases and approaches 37 weeks that are usual for independant life. (Give examples of hormones and inflammatory proteins)

Some of the features that are typical at varying gestational ages are summarized below: (Please note that these features are included for educational purposes, and not because they specifically "make" a diagnosis of a particular gestational age.)

25-26 weeks: This is about the limit for prematurity in which the baby has a reasonable chance at survival.

27-28 weeks:

29 weeks: "The pupils are normally relatively dilated until 29 weeks of gestation, at which time the pupillary light response first becomes apparent." (reference for quote: Douglas R. Fredrick, MD:Chapter 17. Special Subjects of Pediatric Interest in Paul Riordan-Eva and John P. Whitcher (Eds) Vaughan & Asbury's General Ophthalmology 16th Edition, Copyright © 2004 by The McGraw-Hill Companies, Inc.)