Viability

VIABILITY, a term denoting in forensic medicine the ability of a fetus to continue life outside the mother's womb. Viability is determined by two factors: sufficient maturity of the fetus and the absence of significantly pronounced developmental defects or diseases. It is impossible to establish with precision the gestational age starting from which a fetus becomes viable. It is known from experience that from the 20th week of pregnancy and even earlier, children can often be born alive, although they usually die immediately. As an exception, fetuses of 25 weeks' gestation have survived, and repeatedly those of 27–29 weeks. Obstetricians place the beginning of viability at the 28th week of intrauterine life, but even they note high mortality at this age, despite clinical conditions and careful nursing. From a forensic medical point of view, the boundaries of viability are defined differently by authors, namely within the range of 30–32 weeks. Taking into account the usually observed less favorable conditions for the survival of the fetus, it would be more accurate to consider 8 lunar months as the minimum term (Kosorotov, Minakov). By this time, the length of the fetus reaches 40 cm, weight 1,500–2,000 g, the skin is reddish, covered everywhere with down (lanugo); the subcutaneous fat layer is still weakly developed, and the child has a senile appearance. The hair on the head is sparse and short. The cartilages of the nose and ears are soft and not fully formed. The nails are only beginning to harden and reach almost to the ends of the fingers on the hands. Sometimes, along the edge of the pupil, remnants of the pupillary membrane, permeated with vessels, are noticeable. In boys, the testicles have either already left the inguinal canal or are in the process of passing through. In girls, the labia are rounded due to fat deposition. In the calcaneus, an ossification center of about 5 mm in diameter is found, and in the talus, one half that size. The convolutions of the brain are clearly defined. In the large intestines, there is quite a lot of meconium. The average weight of the placenta is 451 g, the average length of the umbilical cord is 46 cm. By the end of the ninth lunar month (36th week), the length of the fetus is approximately 44 cm, the average weight 2,000 g, the skin is already pale pink, fat deposits increase, and the down begins to disappear. The average weight of the placenta is 461 g, the average length of the umbilical cord is 47 cm. After 8 lunar months have passed, the viability of the fetus, its resistance to external influences, is not established immediately, but increases gradually as it approaches the term of normal birth. To judge the degree of viability, body length is of great importance, on the basis of which one can determine the age of intrauterine life of the fetus with accuracy suitable for practical purposes. For this purpose, if the body length does not exceed 25 cm, the square root is extracted from the number of centimeters of body length; with greater height, the number of centimeters is divided by 5. Examples: fetus length 9 cm — 3 lunar months; fetus length 40 cm — 8 lunar months. Less often than from prematurity, non-viability depends on 1) malformations, such as: acephaly, atresia of the intestine, mouth, diaphragmatic hernia, ectopia of the heart, anomalies of its development, obstruction of the pulmonary artery, cystic kidneys, etc.; however, developmental defects do not exclude short-term life; 2) pathological changes lead to the same consequences, e.g., severely pronounced congenital syphilis, and injuries associated with the act of birth, e.g., compression of the head and hemorrhage into the cranial cavity; 3) finally, a fetus born alive may turn out to be non-viable due to blockage of the airways with mucus and the entry of amniotic fluid into them, as happens with the premature onset of respiratory movements. In general, the natural death of a fetus due to non-viability is more probable the earlier it is born before the expiration of the normal term of pregnancy.