Gestational age determination
Gestational age determination is the process of calculating the age of a fetus or newborn based on the time elapsed since the mother's last menstrual period. This measurement is significant in various contexts, including legal cases concerning fetal viability, which refers to a fetus's ability to survive outside the womb. Typically measured in weeks, gestational age begins at two weeks before conception, making it consistently two weeks greater than the fetus’s developmental age. A normal pregnancy spans about 40 weeks, with full-term births occurring between 38 and 42 weeks.
Fetal development occurs in a structured manner, with specific milestones reached at designated gestational ages. Techniques used to estimate gestational age include examining the size of the long bones in deceased fetuses or assessing organ development through medical imaging of intact fetuses. The determination of gestational age holds importance in assessing the potential for a fetus to survive independently, which has become increasingly significant with advancements in neonatal care. Understanding gestational age can also play a critical role in legal proceedings, particularly those involving cases of fetal demise due to external factors.
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Gestational age determination
DEFINITION: Calculation of the age of a fetus or newborn based on the time of the mother’s last menstrual period.
SIGNIFICANCE: In certain legal cases involving the deaths of fetuses, the charges brought depend on whether the fetuses would have been viable—that is, able to live outside the womb—at the time of death. The viability of a fetus can usually be determined based on its gestational age.
Gestational age is measured in weeks based on the time since the mother’s last menstrual period. Most women have a 28-day menstrual cycle, although both longer and slightly shorter cycles are considered normal. Conception, the fertilization of an egg by sperm, normally occurs at the midpoint of the cycle, around day 14. Because gestational age is calculated from the woman’s last menstrual period, at conception, the embryo has a gestational age of two weeks; the gestational age is thus always two weeks greater than the conceptional or developmental age of the fetus. A normal pregnancy ends at forty weeks, or 280 days, gestational age, with babies being born between thirty-eight and forty-two weeks considered normal.
Fetal development happens in an orderly way, with certain developmental events occurring at specific gestational times. When a dead fetus is brought to a pathologist, the pathologist can use several methods to judge the gestational age of the fetus. If the fetus has decomposed, one common method is to measure the middle part of the long bones of the leg that have hardened into bone (the ends of the bones do not harden because they are still growing). Bones that can be used for this calculation include the femur (thighbone), tibia, or fibula (lower-leg bones). The measurements are then plugged into an equation that gives the gestational age. Certain measurements of facial bones can also give an accurate estimate of gestational age. If the fetus is intact, the development of various organs, such as the lungs, will help solidify an estimate of gestational age made through the examination of X-rays of the bones.
Gestational age is important in determining whether the fetus would have been able to live outside the mother’s body. With improvements in the technologies available for treating premature babies, the age of viability for fetuses has steadily decreased. In cases in which a woman is killed in late-term pregnancy, resulting in the death of her fetus, and in some cases of illegal late-term abortion, charges may be filed for of the fetus if it had reached an age where survival outside the mother was likely.
Bibliography
Harding, Richard and Alan D. Bocking. Fetal Growth and Development. New York: Cambridge University Press, 2001.
Huxley, Angie, Richard Froede, and Walter Birkby. “Strangulation of Pregnant Woman Leads to One First-Degree Murder Indictment for the Death of the Mother: A Medicolegal Reconsideration of Maternal/Fetal Homicide.” American Journal of forensic Medicine and Pathology 22 (March, 2001): 51-54.
James, Stuart H., and Jon J. Nordby, eds. Forensic Science: An Introduction to Scientific and Investigative Techniques. 2d ed. Boca Raton, Fla.: CRC Press, 2005.
Niel, Melissa, et al. "Age-at-Death Estimation of Fetuses and Infants in Forensic Anthropology: A New “Coupling” Method to Detect Biases Due to Altered Growth Trajectories." Biology (Basel), vol. 11, no. 2, Feb. 2022, doi.org/10.3390/biology11020200. Accessed 14 Aug. 2024.
Oka, Hiroko, et al. "Age Estimation Using Post-Mortem Computed Tomography and Fetal Dental Radiographic Findings in an Early to Mid-Pregnancy Fetus: A Case Report." Legal Medicine, vol. 62, May 2023, doi.org/10.1016/j.legalmed.2023.102232. Accessed 14 Aug. 2024.