The universal definition of “full-term” pregnancy, with its emphasis on reducing preterm birth and increasing planned deliveries, has created confusion about the concept of full-term pregnancy. The concept of “full-term” pregnancy provides clinicians with guidelines and influences the public perception of the optimal timing of delivery for a healthy pregnancy. Full-term birth is currently defined as births other than preterm and term pregnancies. Preterm birth is classically defined as birth at less than 37 weeks from the start of the last menstrual period, and term birth is defined as birth at more than 42 weeks; therefore, the traditional concept of full-term birth is birth at 37 to 42 weeks. According to the international classification of diseases, a full-term birth is a birth between 37 weeks and 0 days and 41 weeks plus 6 days. In 2005, a working group of the National Institute of Child Health and Human Development renamed deliveries between 34 weeks 0 days and 36 weeks plus 6 days of gestation from near full term to late preterm birth to emphasize that the morbidity and mortality rates of these newborns are similar to those of preterm infants and to highlight the adverse consequences of delivery before 37 weeks of gestation. This nomenclature recognizes fetal maturation as a continuum, however, the term “full-term” pregnancy remains unchanged for deliveries between 37 weeks 0 days and 41 weeks plus 6 days of gestation. Recent data suggest that the incidence of adverse maternal and neonatal outcomes during full-term pregnancies spanning 6 gestational weeks varies, with a U-shaped pattern and a nadir at approximately 39 weeks and 0 days to 40 weeks plus 6 days. Until more accurate methods became available, the date of the last menstrual period was the main method of calculating the weeks of gestation, as women usually did not remember the date of conception but rather the date of menstruation. With the advent of ultrasound, pregnancy tests, assisted reproductive technology and ovulation test kits, the actual time of conception and subsequent gestational age can be determined more accurately than in the past. Therefore, it becomes inappropriate to continue with the same wide gestational week definition of full-term birth that was previously used to determine the less precise period of date. To further refine the definition of full-term pregnancy, the National Institute of Child Health and Human Development, the American College of Obstetricians and Gynecologists, the American Academy of Pediatrics, the Society for Maternal-Fetal Medicine, the Birth Defects Foundation, and the World Health Organization (WHO) convened an expert meeting in Bethesda, Maryland, on December 17, 2012, and the recommendations from this meeting are reported here. Current outcomes of full-term pregnancies in the United States, demographics suggest a shift toward earlier gestational weeks in the last few years. The risk of fetal death is higher for deliveries beyond 42 weeks 0 days of gestation than for pregnancies between 38 weeks 0 days and 41 weeks plus 6 days, and the risk of death is higher for pregnancies between 37 weeks 0 days and 38 weeks plus 6 days than for pregnancies between 39 weeks and 41 weeks plus 6 days. Infants born at 39 weeks 0 days to 41 weeks 0 days had the lowest mortality rate. The incidence of neonatal respiratory distress syndrome, the use of ventilators, and admission to the neonatal intensive care unit showed the lowest incidence from 39 weeks 0 days to 40 weeks plus 6 days of gestation, with higher incidence in both the first (37-38 weeks) and subsequent (41-42 weeks) groups. In general, it appears that the ability to assess risk and trends based on the length of full-term pregnancy (37 weeks 0 days to 41 weeks plus 6 days) is limited to mortality and not to morbidity.WHO has conducted multi-country basic surveys on birth outcomes.WHO multi-country survey studies on maternal and newborn health show that the average week of gestation at delivery in all countries ranges from 38.5 to 38.9 weeks; relative to The risk of early neonatal death and stillbirth was elevated for deliveries at 37 weeks 0 days to 38 weeks plus 6 days, relative to 39 weeks 0 days to 40 weeks plus 6 days (corrected OR 1.21 (95% CI, 1.03-1.41) for the former and 1.31 (95% CI, 1.09-1.58) for the latter). Thus, in the United States and low- and middle-income countries, infants delivered at 37 weeks 0 days to 38 weeks plus 6 days of gestation are at higher risk of neonatal morbidity and mortality than those born at 39 weeks 0 days to 41 weeks plus 6 days of gestation. Redefining full-term pregnancy Given what is known today about the increased adverse perinatal outcomes associated with deliveries at 37 to 38 weeks and 41 to 42 weeks compared to 39 to 40 weeks of gestation, how should full-term pregnancy be redefined? The workshop participants agreed that there is variability in fetal maturity and prognosis between 37 weeks 0 days and 41 weeks plus 6 days and that the timing of full-term pregnancy requires further subclassification. The working group recommended that deliveries between 37 weeks 0 days and 38 weeks plus 6 days be specifically referred to as early full-term births, and deliveries between 39 weeks 0 days and 40 weeks plus 6 days of gestation as full-term births; it also recommended that deliveries between 41 weeks 0 days and 41 weeks plus 6 days be mentioned as late full-term births. This classification has implications for prenatal counseling, management, and research. Given the known increased morbidity and mortality of deliveries before 39 weeks, it is important not to terminate a pregnancy before then without a medical indication. It is also important to emphasize the appropriateness of an early full-term stage of labor for medically indicated terminations or spontaneous labor or spontaneous rupture of membranes from 37 weeks 0 days to 38 weeks plus 6 days of gestation. The definition, subclassification of preterm and full-term births implies the need for precise determination of the week of gestation, and this exact date will likely result in a lower rate of classification as a term birth or early full-term birth. The most accurate method of estimating gestational age for those women conceived other than through assisted reproductive technology is obtained by ultrasound in early pregnancy, and although once recommended by the American Medical Association, this working group believes that a universal policy of mandatory early pregnancy ultrasound is generally unrealistic. Therefore, for women with a definite date of last menstruation, it is sufficient to wait until 18 to 20 weeks of gestation to determine gestational age by ultrasound of the fetus while screening for fetal anatomy. In contrast, women with an ambiguous date of last menstrual period should have an early ultrasound examination to determine the gestational week. A suggested method for determining the gestational age is shown in Fig. Conclusion The use of “full-term pregnancy” as a stand-alone definition should be inappropriate because it covers a wide range of gestational weeks, is accompanied by different levels of infant and maternal risk, and undermines the practice and efforts of evidence-based medicine to limit delivery before 39 weeks of non-medically indicated pregnancy. This working group recommends that the six gestational weeks previously defined as encompassing full-term pregnancy be subdivided here into early full-term, full- and late-full-term, and past-term pregnancies. Communication of these precise and reasonable classifications is necessary. The use of precise language by clinicians and the public can potentially influence the choice of timing of delivery, thereby benefiting the health of women and children.