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Periviable birth (Limit of viability)

Authors
Richard A Ehrenkranz, MD, FAAP
Mark R Mercurio, MD, MA
Section Editor
Richard Martin, MD
Deputy Editor
Melanie S Kim, MD

INTRODUCTION

Periviability, also referred to as the limit of viability, is defined as the stage of fetal maturity that ensures a reasonable chance of extrauterine survival. With active intervention, most infants born at 26 weeks and above have a high likelihood of survival, and virtually none below 22 weeks will survive. The chance of survival thus increases dramatically over these few weeks, and this crucial time window may be considered the period of periviability. In addition to the high risk of death in the immediate newborn period, children born at the limit of viability have a high risk of permanent disability. An understanding of both of these risks is essential to parental counseling and decision-making, with regard to attempted resuscitation and provision of life-sustaining measures in the newborn intensive care unit (NICU).

Survival and morbidity of extremely preterm infants born below 26 weeks gestation will be reviewed. In addition, a management approach for infants born in the periviable period, based upon prognosis, will be presented. The management of pregnancies at or near the limit of viability is discussed separately. (See "Delivery of the preterm low birth weight singleton fetus", section on 'Management at the limit of viability'.)

SURVIVAL RATES

Factors that affect survival rates in extremely preterm infants (gestational age [GA] <26 weeks) include GA, birth weight (BW), gender, plurality, and the use of antenatal corticosteroid therapy [1-3].

Gestational age — The major factor in determining viability is GA. Survival rates reported in a number studies [1,4-18] during the initial neonatal intensive care unit (NICU) admission for infants 22 to 25 completed weeks gestation (220/7 to 256/7 weeks gestation) are displayed in the table (table 1). These reports span time periods ranging from six months to six years between 1993 and 2014, and represent several large geographic areas in Western Europe, Japan, a network of tertiary level academic centers in the United States, and a population-based study of California. These data clearly demonstrated the rise of survival rate as GA increased from 22 to 25 weeks, as well as improvement in survival of periviable infants over the past two decades.

These publications and the changes in outcome emphasize the importance of basing discussions about delivery room management for periviable infants upon the latest available data. In addition, although these results highlight the impact of GA on viability, it is important to recognize that ascertaining an accurate GA is challenging. Thus, estimated GA alone may not truly reflect the prognosis. (See 'Interpreting the data' below and "Postnatal assessment of gestational age" and "Prenatal assessment of gestational age and estimated date of delivery".)

                  

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Literature review current through: Feb 2017. | This topic last updated: Fri Mar 24 00:00:00 GMT+00:00 2017.
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