December 2011, VOLUME128 /ISSUE 6

Limits of Human Viability in the United States: A Medicolegal Review

  1. Bonnie Hope Arzuaga, MDa,b,
  2. Ben Hokew Lee, MD, MPH, MSCRb,c
  1. aSection of Neonatology, Department of Pediatrics, University of Chicago Medical Center, Chicago, Illinois; and
  2. bDepartment of Pediatrics, Goryeb Children's Hospital, and
  3. cMidAtlantic Neonatal Research Institute, Morristown Medical Center at Atlantic Health, Morristown, New Jersey

Throughout American history, medical and legal definitions of human viability have evolved on interrelated but slightly different trajectories. In the early 19th century, although common law did not consider abortion to be a criminal offense, it was discouraged after the onset of quickening, which connected the initial delineation of viability to the sensation of fetal movement within the womb. When post–Civil War physicians campaigned to outlaw abortion, it was transformed into a criminal act, because societal attitudes had redefined human life as beginning at conception.1

In 1935, the American Academy of Pediatrics defined a premature infant as one who weighed <2500 g at birth regardless of gestational age,2 a standard first adopted in Europe in 1919.3 Although no minimum weight for viability was established, 1250 g was frequently used and corresponded to an estimated gestational age (EGA) of 28 weeks.2,4 In the mid-20th century, the addition of gestational age and crown-to-heel length to assist with the definition of viability was advocated.5,6

In the 1950s, infantile respiratory distress syndrome was described to the Royal College of Obstetricians and Gynaecologists of the United Kingdom7 and identified as a principal cause of death in infants younger than 37 weeks' EGA. This led to a landmark distinction between “premature” and “growth-restricted” infants who weighed <2500 g at birth.8 In the ensuing decades, neonatal mechanical ventilation and parenteral nutrition became established as contemporary cornerstones of neonatal medicine. Although the mortality rate of infants born at <1800 g was not significantly altered by initial intermittent positive-pressure ventilator strategies,9 the subsequent advent of continuous positive airway pressure in the 1970s markedly improved these outcomes.10,11 As neonatal total parenteral nutritional therapy became increasingly mainstream,12 the medical definition of viability continued to evolve as well.

During this time, the landmark US Supreme Court case of Roe v Wade legalized abortion in the United States. This legislation developed a trimester framework for gestational age, establishing that abortions in the third trimester could be performed only if the health of the mother was in jeopardy, which implied that a fetus was legally viable at 28 weeks.13 Subsequent cases during this decade failed to establish alternative legal definitions of viability. In 1976, Planned Parenthood of Central Missouri v Danforth determined that viability was achieved at different times for each pregnancy and, therefore, was a matter of judgment of the attending physician.14 Three years later, Colautti v Franklin rejected a Pennsylvania statute that would have required physicians to protect the life of a potentially viable fetus either during or after an abortive procedure, ruling instead that the determination of viability was to be performed on a case-by-case basis.15

In 1978, the first infants who weighed <750 g were successfully ventilated16; by the 1980s, survival of infants who were born weighing 500 to 700 g or were of 24 to 26 weeks' gestation became an expected possibility in regional NICUs, which anecdotally established these characteristics as contemporary limits of viability.16,17 With extremely low birth weight infants at the limits of viability surviving beyond the postnatal period, the study of long-term outcomes, particularly neurodevelopmental impairment and growth failure, became increasingly important.16,,19 The 1980s and 1990s brought new waves of neonatal biomedical advances, led by tracheal instillation of surfactant for respiratory distress syndrome20,,22 and the use of antenatal corticosteroids in women with imminent delivery of a preterm infant at 24 to 34 weeks' gestation.23 With these changes, survival of infants born at 23 and 24 weeks' EGA became increasingly frequent.24,,26

Although the medical limit of viability began to enter into the second trimester, the legal definition of this limit continued to defy strict delineation. In 1989, Webster v Reproductive Health Services declined to uphold a provision that required physicians to test for fetal viability before performing an abortion of fetuses aged 20 weeks' EGA or older.27 Three years later, in the seminal case of Planned Parenthood of Southeastern Pa. v Casey, the Courts abandoned Roe's landmark trimester framework and adopted previability and postviability statutes. In this decision, the Court stated, “Whenever viability may occur, be it at 23–24 weeks, the standard at the time, or earlier, as may be the standard sometime in the future, the attainment of viability serves as the critical fact in abortion legislature.28

The legal limit of viability continued to be restructured with the Born Alive Infants Protection Act (BAIPA) of 2002. This act aimed to protect infants born with signs of life regardless of gestational age or whether the birth was a product of an abortive procedure. Subsequently, the US Department of Health and Human Services announced that it would uphold the BAIPA and use it to investigate alleged violations of the Emergency Medical Treatment and Labor Act (EMTALA), including claims of an infant “suffering from an emergency medical condition” not being medically evaluated.29,30 In 2004, Preston v Meriter Hospital Inc used this policy in litigation against hospital staff who chose not to attempt resuscitation of a 700-g 23-week-gestation newborn, claiming that the infant was not provided appropriate medical screening in violation of the EMTALA. The hospital's counsel argued that because the infant was born in the labor and delivery unit, the EMTALA did not apply. On this count, the appeals court ruled in favor of the plaintiff, stating that the infant deserved screening by a physician regardless of the actual department in which he was born, which made the EMTALA a mandate capable of enforcing a medical determination of viability for infants born at the margins of viability, regardless of the actual birth weight, gestational age, or location within a hospital.31

At present, specific regulations on abortion limits or legal definitions of viability have been delegated to the individual states and territories of the United States (Table 1); the majority of these statues have deferred judgment of viability to the attending physician.32 Of those that state or infer a gestational limit of viability, the limit ranges from 19 to 28 weeks.33,,47 Alabama has the strictest limitations, dictating that after 19 weeks' gestation, a physician must determine in “good faith medical judgment” whether the child is viable before performing an abortion.45 Texas has a notable caveat to its viability definition in that it excludes any fetus whose biparietal diameter is <60 mm.46


Individual State and Territory Statutes Pertaining to Viability and/or Abortion Restrictions

Under contemporary standards of care, the decision to resuscitate a 22- or 23-week infant is guided by antenatal bioethical deliberations and perinatal evaluations estimating the fetoneonatal probability of survival, including birth weight, EGA, and clinical appearance, as imperfect as these assessments may be.48 A mandate for neonatal resuscitation to include a “trial of life” for infants born at the limit of viability may result in an increase in overall, but not necessarily medically or neurodevelopmentally intact, survival of extremely premature infants.49 Recently, among resuscitated infants who weighed >400 g at birth, ∼6% of 22 weeks' EGA infants and 26% of 23 weeks' EGA infants were reported to survive to NICU discharge, which illustrates a contemporary definition of human viability.50 As the medical and legal definitions of fetal viability continue to redefine themselves, their interrelationships will continue to be refined and debated as well.


We thank Lauren L. Straub, JD candidate, for assistance with the legal body of literature.


    • Accepted September 23, 2011.
  • Address correspondence to Bonnie Hope Arzuaga, MD, Comer Children's Hospital at University of Chicago, 5721 S Maryland Ave, Chicago, IL 60637. E-mail: bonniehope{at}
  • Drs Arzuaga and Lee made substantial contributions to the conception and design of and the acquisition of data for this article; Dr Arzuaga drafted the initial version, which was then revised critically by Dr Lee. Both authors reviewed the final version of the article before submission.

  • FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.

  • EGA
    estimated gestational age


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