“Pregnancy is so exhausting, let the baby come out after 37 weeks full term.” “Doctor, I’ve counted the days, I want a C-section at 38 weeks.” Chinese people are most concerned about reading the yellow calendar, and this preoccupation is even reflected in the birth of a child. Many parents believe that the year, month, day and even hour of a baby’s birth is inextricably linked to its fate in life. With this kind of thinking, many mothers will choose an auspicious time and day to have a C-section and give birth to their babies, even if that auspicious day and hour is still far away from the due date. Have you ever moved to a similar thought? Delivery during 37 weeks and less than 42 weeks of pregnancy is called a full-term labor. This definition of full term has not changed since it was established in 1970 by the Second European Society of Perinatal Medicine. Based on this definition, many expectant mothers think it’s perfectly fine to bring their babies out early after 37 weeks of pregnancy, because they’re full-term anyway. In fact, we often see newborns who are delivered by C-section or even induced before 39 weeks due to personal reasons of the pregnant woman. They are covered with fetal fat, the amniotic fluid is clear, and the nails and hair have not started to grow vigorously, which are all signs that the baby is not mature enough. Even serious complications of the respiratory system such as immature newborn lungs can occur in severe cases. In recent years, more and more studies have shown that the immediate and long-term prognosis of full-term babies born beyond 37 weeks differ significantly with the gestational week of birth. Gestational age, a persistent biological factor, continues to have a similar dose-effect relationship even in the term range. Full-term infants at 37 or 38 weeks of gestation have a clear advantage over full-term infants after 39 weeks of gestation in terms of lung maturation and brain development, and in terms of complications such as hypoglycemia, pathologic jaundice, and infections. The last few weeks after full-term allow for adequate maturation of the baby’s lungs and brain, and the incidence of each of these complications is much smaller. Full-term babies before 39 weeks are not preterm, but they are more deceptive than preterm babies. Fetuses born before 39 weeks are not naturally born, they are less adapted to the intrauterine-extrauterine transition and are at increased risk of independent survival after birth, an adverse effect that can last into infancy. As the old saying goes: a day in the belly is better than a week outside – although there is no strict scientific truth to this statement. A 2013 report published in the American Journal of Obstetrics and Gynecology offers an updated perspective, dividing full-term pregnancies into four stages: early term: 37 weeks 0 days to 38 weeks 6 days; full term: 39 weeks 0 days to 40 weeks 6 days; late term: 41 weeks 0 days to 41 weeks 6 days; and overripe: >42 weeks. The paper concluded that only newborns born between 39 and 41 weeks are full-term infants in the true sense of the word. This new definition, endorsed by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, is designed to discourage physicians and patients from unnecessarily inducing labor or performing a cesarean section too early (less than 39 weeks). Instead, planned inductions or cesarean deliveries before 39 weeks should only occur in pregnant women with definite pregnancy complications. For example, placenta praevia, for example, multiple pregnancies, for example, preeclampsia and other hypertensive disorders or poorly controlled gestational diabetes. At this point, the obstetrician should weigh the pros and cons and choose the appropriate week of gestation for induction of labor or cesarean section while trying to ensure the safety of the mother and baby, nor should he or she expose the mother and baby to higher risks by seeking maturity of gestational age. Of course, some pregnant women may go into labor earlier than 39 weeks, but we usually believe that such natural labor is also a sign of fetal placental maturity, and there is no need to worry too much about it.