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 and infants are compiled, premature infants are overrepresented.

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 at birth

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 due 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 other words, many of the babies who are born long before they are expected, but are born with the appearance and size of full term, or near full term infants are likely not premature but, instead, their mothers had been given the wrong estimated date of confinement.

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.)

Premature neonates around the world

"Approximately 4 million children are born in the United States each year, of which approximately 11% are premature... 1% of these low birth weight (LBW) infants are less than 1,500 grams at birth and more than 80% of these very-low-birth-weight (VLBW) infants survive to discharge. A significant minority, 20-40%, of the very-low-birthweight babies have complex medical problems." Verma RP. Sridhar S. Spitzer AR. Continuing care of NICU graduates. Clinical Pediatrics. 42(4):299-315, 2003 May. UI: 12800725

Neonatal intensive care unit

In countries offering technilogically advanced medical care, special units for the care of premature and other ill newborns called neonatal instensive care units exist. If a baby requires support of breathing with mechanical ventilation, then admission to the neonatal ICU is usual.

Discharge from the hospital

The criteria used to determine if a baby is ready to be discharged vary from hospital to hospital, but there are some generalizations that may be made. The baby who is ready to go home to his parent's care is usually able to feed by a nipple (bottle or breast), and is gaining weight adequately with such feeding. He no longer requires an "incubator"- that is a temperature-controlled environment, but can maintain his body temperature in a crib or bassinet. The baby is not having periods of abnormal heart rhythyms that are potentially lifethreatening, or lifethreatening periods of apnea.

Even once the premature baby is no longer obviously small, the immaturity of his organ systems puts him at greater risk than a full term infant.

Continuing care of premature infants after discharge

Premature babies who require care in the neonatal intensive care unit are sometimes offered specialized care after discharge.

References

Verma RP. Sridhar S. Spitzer AR. Continuing care of NICU graduates. [Review] [102 refs] [Journal Article. Review] Clinical Pediatrics. 42(4):299-315, 2003 May. UI: 12800725