Fetal viability

Viability, as the word has been used in United States constitutional law since Roe v. Wade, is the potential of the fetus to survive outside the uterus after birth, natural or induced, when supported by up-to-date medicine. Fetal viability depends largely on the fetal organ maturity, and environmental conditions.[2] According to Websters Encyclopedic Unabridged Dictionary of the English Language, viability of a fetus means having reached such a stage of development as to be capable of living, under normal conditions, outside the uterus. Viability exists as a function of biomedical and technological capacities, which are different in different parts of the world. As a consequence, there is, at the present time, no worldwide, uniform gestational age that defines viability.[3]

According to the McGraw-Hill medical dictionary a nonviable fetus is "an expelled or delivered fetus which, although living, cannot possibly survive to the point of sustaining life independently, even with support of the best available medical therapy."[4] A legal definition states: "Nonviable means not capable of living, growing, or developing and functioning successfully. It is antithesis of viable, which is defined as having attained such form and development of organs as to be normally capable of living outside the uterus." [Wolfe v. Isbell, 291 Ala. 327, 329 (Ala. 1973)][5]

Various jurisdictions have different legal definitions of viability. In Ireland, under the Health (Regulation of Termination of Pregnancy) Act 2018, fetal viability is defined as "the point in a pregnancy at which, in the reasonable opinion of a medical practitioner, the foetus is capable of survival outside the uterus without extraordinary life-sustaining measures." [Definitions (Part 2)(8)][6]

Preterm infants survival rates based on different studies.[7][8][9][10][11][12]

There is no sharp limit of development, gestational age, or weight at which a human fetus automatically becomes viable.[1] According to studies between 2003 and 2005, 20 to 35 percent of babies born at 24 weeks of gestation survive, while 50 to 70 percent of babies born at 25 weeks, and more than 90 percent born at 26 to 27 weeks, survive.[13] It is rare for a baby weighing less than 500 g (17.6 ounces) to survive.[1] The chances of a fetus surviving increase 3-4% per day between 23 and 24 weeks of gestation and about 2-3% per day between 24 and 26 weeks of gestation. After 26 weeks the rate of survival increases at a much slower rate because survival is high already.[14][15][16][17]

Stages in prenatal development, showing viability and point of 50% chance of survival (limit of viability) at bottom. Weeks and months numbered by gestation.

The period of viability refers (traditionally) to the period after the twenty-eighth week,[18] or more recently the twenty-fourth week, of gestation when a human fetus is capable of living outside of the womb. Whether the fetus is in the period of viability has legal ramifications as far as the fetus' rights of protection are concerned.[19]

It sometimes incorporates weight as well as gestational age.[20][21][22]

The limit of viability is the gestational age at which a prematurely born fetus/infant has a 50% chance of long-term survival outside its mother's womb. With the support of neonatal intensive care units, the limit of viability in the developed world has declined since 50 years ago.[30][31]

Currently, the limit of viability is considered to be around 24 weeks, although the incidence of major disabilities remains high at this point.[32][33] Neo-natologists generally would not provide intensive care at 23 weeks, but would from 26 weeks.[34][35][36]

Different jurisdictions have different policies regarding the resuscitation of extremely premature newborns, that may be based on various factors such as gestational age, weight and medical presentation of the baby, the desires of parents and medical practitioners. The high risk of severe disability of very premature babies or of mortality despite medical efforts lead to ethical debates over quality of life and futile medical care, but also about the sanctity of life as viewed in various religious doctrines.[37]

As of 2006, the two youngest children to survive premature birth are thought to be James Elgin Gill (born on 20 May 1987 in Ottawa, Ontario, Canada, at 21 weeks and 5 days gestational age),[38][39] and Amillia Taylor (an IVF pregnancy, born on 24 October 2006 in Miami, Florida, at 21 weeks and 6 days gestational age).[40][41] Both children were born just under 20 weeks from fertilization (or 22 weeks' gestation). At birth, Taylor was 9 inches (22.86 cm) long and weighed 10 ounces (283 grams).[40] She suffered digestive and respiratory problems, together with a brain hemorrhage. She was discharged from the Baptist Children's Hospital on 20 February 2007.[40] As of 2013, Taylor was in kindergarten and at the small end of the normal growth curve with some developmental delays.[42]

A preterm birth, also known as premature birth, is defined as babies born alive before 37 weeks of pregnancy are completed.[43] There are three types of preterm births: extremely preterm (less than 28 weeks), very preterm (28 to 32 weeks) and moderate to late preterm (32 to 37 weeks).[43]

There are several factors that affect the chance of survival of the baby. Two notable factors are age and weight. The baby's gestational age (number of completed weeks of pregnancy) at the time of birth and the baby's weight (also a measure of growth) influence whether the baby will survive. Another major factor is gender: male infants are slightly less mature and have a slightly higher risk of dying than female infants.

Several types of health problems also influence fetal viability. For example, breathing problems, congenital abnormalities or malformations, and the presence of other severe diseases, especially infection, threaten the survival of the neonate.

Other factors may influence survival by altering the rate of organ maturation or by changing the supply of oxygen to the developing fetus.

The mother's health plays a significant role in the child's viability. Diabetes in the mother, if not well controlled, slows organ maturation; infants of such mothers have a higher mortality. Severe high blood pressure before the 8th month of pregnancy may cause changes in the placenta, decreasing the delivery of nutrients and/or oxygen to the developing fetus and leading to problems before and after delivery.

Rupture of the fetal membranes before 24 weeks of gestation with loss of amniotic fluid markedly decreases the baby's chances of survival, even if the baby is delivered much later.[14]

The quality of the facility—whether the hospital offers neonatal critical care services, whether it is a Level I pediatric trauma care facility, the availability of corticosteroids and other medications at the facility, the experience and number of physicians and nurses in neonatology and obstetrics and of the providers has a limited but still significant impact on fetal viability. Facilities that have obstetrical services and emergency rooms and operating facilities, even if smaller, can be used in areas where higher services are not available to stabilize the mother and fetus or neonate until they can be transferred to an appropriate facility.[44][16][45][46]

• Beginning of human personhood
• Futile medical care
• Office for Human Research Protections#Additional protection for pregnant women, human fetuses, and neonates