question: why babies don't suffocate inside the womb during the latest stages of pregnancy?
comment: Their circulatory systems are connected to the mother’s through the umbilical cord. Therefore, they are receiving oxygenated blood and don’t need to breathe.
passages: At any age, if the fetal well-being appears to be compromised, or if intrauterine infection is suspected, the baby should be delivered quickly by induction of labour.
  
  Section::::Management.:Term.
   Section::::Role of the placenta.
  
  The healthy placenta is a semipermeable membrane that does form a barrier for most pathogens and for certain xenobiotic substances. However, it is by design an imperfect barrier since it must transport substances required for growth and development. Placental transport can be by passive diffusion for smaller molecules that are lipid soluble or
   A fetus, receiving oxygen via the placenta, is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), so fetuses produce another form of hemoglobin with a much higher affinity for oxygen (hemoglobin F) to function under these conditions.
  
  Section::::Physiology.:Carbon dioxide transport.
   Sometimes, a child is born with no rupture of the amniotic sac (no rupture of membranes). In such cases, the child may still be entirely within the sac once born; such a birth is known as an en-caul birth.
  
  Section::::Effects.
  
  When the amniotic sac ruptures, production of prostaglandins increases and the cushioning between the fetus and uterus is decreased, both of which are processes that increase the frequency and intensity of contractions.
   The key pollutant for infant mortality rates is carbon monoxide. Carbon monoxide is a colorless, odorless gas that does great harm especially to infants because of their immature respiratory system.
   At birth, the baby's lungs are filled with fluid secreted by the lungs and are not inflated. After birth the infant's central nervous system reacts to the sudden change in temperature and environment. This triggers the first breath, within about 10 seconds after delivery. Before birth, the lungs are filled with fetal lung fluid. After the first breath, the fluid is quickly absorbed into the body or exhaled. The resistance in the lung's blood vessels decreases giving an increased surface area for gas exchange, and the lungs begin to breathe spontaneously. This accompanies other changes which result in an increased amount of blood entering the lung tissues.
   When such premature babies are born, the main causes of mortality are that the respiratory system and the central nervous system are not completely differentiated. If given expert postnatal care, some preterm babies weighing less than may survive, and are referred to as "extremely low birth weight" or "immature infants".
  
  Preterm birth is the most common cause of infant mortality, causing almost 30 percent of neonatal deaths. At an occurrence rate of 5% to 18% of all deliveries, it is also more common than postmature birth, which occurs in 3% to 12% of pregnancies.
  
  Section::::Circulatory system.
  
  Section::::Circulatory system.:Before birth.
   Sometimes these postnatal closures are incomplete or absent. The vessels or cross-connections remain open (patent), leading to the following conditions: 
  
  BULLET::::- Patent foramen ovale in the heart
  
  BULLET::::- Patent ductus arteriosus in the great vessels
  
  BULLET::::- Patent ductus venosus in the great vessels
  
  Section::::Structure.:Adult remnants.
  
  Remnants of the fetal circulation can be found in the adult.
   Section::::Management.:Before 24 weeks.
  
  Before 24 weeks, a fetus is not viable meaning it cannot live outside the mother. In this case, either watchful waiting at home or an induction of labor done.
   The 1950s brought a rapid escalation in neonatal services with the advent of mechanical ventilation of the newborn. This allowed for survival of smaller and smaller newborns. In the 1980s, the development of pulmonary surfactant replacement therapy further improved survival of extremely premature infants and decreased chronic lung disease, one of the complications of mechanical ventilation, among less severely premature infants. In 2006 newborns as small as 450 grams and as early as 22 weeks gestation have a chance of survival. In modern NICUs, infants weighing more than 1000 grams and born after 27 weeks gestation have an approximately 90% chance of survival and the majority have normal neurological development.
   In addition to differences in circulation, the developing fetus also employs a different type of oxygen transport molecule in its hemoglobin from that when it is born and breathing its own oxygen. Fetal hemoglobin enhances the fetus' ability to draw oxygen from the placenta. Its oxygen-hemoglobin dissociation curve is shifted to the left, meaning that it is able to absorb oxygen at lower concentrations than adult hemoglobin. This enables fetal hemoglobin to absorb oxygen from adult hemoglobin in the placenta, where the oxygen pressure is lower than at the lungs. Until around six months' old, the human infant's hemoglobin molecule is made up of two alpha and two gamma chains (2α2γ). The gamma chains are gradually replaced by beta chains until the molecule becomes hemoglobin A with its two alpha and two beta chains (2α2β).
   4. To avoid having the baby aspirate the contents of the amniotic sac at the moment of birth. Most often, the amniotic sac will break of its own accord, most often by the beginning of the second stage of labor. If it remains intact, it is sure to break with maternal pushing efforts. But in a rare case, the baby can be born with an intact bag that must be quickly broken to allow the baby to breathe.
   The majority of infants who have survived following an incidence of bronchopulmonary dysplasia will eventually recover near-normal lung function, since lungs continue to grow during the first 5–7 years and the damage caused by bronchopulmonary dysplasia is to some extent reversible (even in adults). However, they are likely to be more susceptible to respiratory infections for the rest of their lives and the severity of later infections is often greater than that in their peers.
   The "ductus arteriosus" normally closes within one or two days of birth, leaving the "ligamentum arteriosum", while the umbilical vein and "ductus venosus" usually closes within two to five days after birth, leaving, respectively, the liver's "ligamentum teres" and "ligamentum venosus".
  
  Section::::Immune system.
  
  The placenta functions as a maternal-fetal barrier against the transmission of microbes. When this is insufficient, mother-to-child transmission of infectious diseases can occur.
   and their appearance around the seventh month marks the point at which limited respiration would be possible, and the premature baby could survive.
  
  Section::::Development.:Vitamin A deficiency.
   Oxygenated blood is delivered to the fetus via the umbilical vein from the placenta, which is anchored to the wall of the mother's uterus. The chorion acts as a barrier between the maternal and fetal circulation so that there is no admixture of maternal and fetal blood. Blood in the maternal circulation is delivered via open ended arterioles to the intervillous space of the chorionic plate, where it bathes the chorionic villi that carry umbilical capillary beds, thereby allowing gas exchange to occur between the maternal and fetal circulation. Deoxygenated maternal blood drains into open ended intervillous venules to return to maternal circulation. Due to the admixture of oxygenated and deoxygenated blood, maternal blood in the intervillous space is lower in oxygen than arterial blood. As such, fetal hemoglobin must be able to bind oxygen with greater affinity than adult hemoglobin in order to compensate for the relatively lower oxygen tension of the maternal blood supplying the chorion.
   Section::::Physiology.
  
  The core concept behind fetal circulation is that fetal hemoglobin (HbF) has a higher affinity for oxygen than does adult hemoglobin, which allows a diffusion of oxygen from the mother's circulatory system to the fetus.
  
  Section::::Physiology.:Blood pressure.
  
  It is the fetal heart and not the mother's heart that builds up the fetal blood pressure to drive its blood through the fetal circulation.
  
  Intracardiac pressure remains identical between the right and left ventricles of the human fetus.
   Congenital disorders are acquired before birth. Infants with certain congenital heart defects can survive only as long as the ductus remains open: in such cases the closure of the ductus can be delayed by the administration of prostaglandins to permit sufficient time for the surgical correction of the anomalies. Conversely, in cases of patent ductus arteriosus, where the ductus does not properly close, drugs that inhibit prostaglandin synthesis can be used to encourage its closure, so that surgery can be avoided.
  
  Other heart birth defects include ventricular septal defect, pulmonary atresia, and tetralogy of Fallot.
  
  Section::::Fetal pain.
   BULLET::::- Suffocation: Babies lack the motor skills or strength to turn their heads should they roll into something that obstructs their breathing. They can become trapped and suffocate if they fall into gaps created by ill-fitting or additional mattresses. Babies can also suffocate if the mattress is too soft.
  
  BULLET::::- Entrapment: Infants can suffer injuries to their arms and legs if they become trapped between gaps. Gaps small enough for a limb to become trapped are not permitted.
   Maternal arteries and veins directly enter the intervillous space after 8 weeks gestation, and the intervillous space will contain about a unit of blood (400-500 mL). Much of this blood is returned to the mother with normal uterine contractions; thus, when a woman has a cesarean section, she is liable to lose more blood than a woman who has a vaginal delivery, as the blood from the intervillous space is not pushed back toward her body during such a delivery.
   Extracorporeal membrane oxygenation (ECMO) is a potential treatment, providing oxygenation through an apparatus that imitates the gas exchange process of the lungs. However, newborns cannot be placed on ECMO if they are under 4.5 pounds (2 kg), because they have extremely small vessels for cannulation, thus hindering adequate flow because of limitations from cannula size and subsequent higher resistance to blood flow (compare with vascular resistance). Furthermore, in infants aged less than 34 weeks of gestation, several physiologic systems are not well-developed, especially the cerebral vasculature and germinal matrix, resulting in high sensitivity to slight changes in pH, PaO and intracranial pressure. Subsequently, preterm infants are at unacceptably high risk for intraventricular hemorrhage (IVH) if administered ECMO at a gestational age of less than 32 weeks.
   Respiration in neonates is very irregular, prone to periodic breathing and apnea. In utero and at birth, the carotid body’s response to hypoxia is not fully developed; it takes a few days to a few weeks to increase its sensitivity to that of an adult carotid body. During this period of development, it is proposed that neonates heavily rely on other oxygen-sensing chemoreceptors, such as the aortic body or central chemoreceptors. However, non-carotid body chemoreceptors are sometimes not enough to ensure appropriate ventilatory response; SIDS deaths occur most frequently during the days or weeks in which the carotid body is still developing, and it is suggested that lack of appropriate carotid body activity is implicated in this condition. SIDS victims often are reported to have displayed some of the characteristic troubles in carotid body development, including periodic breathing, much sleep apnea, impaired arousal during sleep, and low sensitivity to hypoxia. The carotid bodies of SIDS victims also often display physiological abnormalities, such as hypo- and hypertrophy. Many of the findings on to carotid body’s relation to SIDS report that carotid body development is impaired by environmental factors that were already known to increase the risk of SIDS, such as premature birth and exposure to smoke, substances of abuse, hyperoxia, and hypoxia, so it may seem initially as if carotid body studies are only extending what we know about SIDS into another domain. However, understanding the mechanisms that impair carotid body development could help elucidate how certain aspects of neonatal, particularly premature, care might be improved. For example, oxygen therapy may be an example of a technique that exposes premature infants to such high oxygen levels that it prevents them from acquiring appropriate sensitivity to normal oxygen levels.
   At any gestational age, an opening in the fetal membranes provides a route for bacteria to enter the womb. This can lead to chorioamnionitis (an infection of the fetal membranes and amniotic fluid) which can be life-threatening to both the mother and fetus. The risk of infection increases the longer the membranes remain open and baby undelivered. Women with preterm PROM will develop an intra-amniotic infection 15–25% of the time, and the chances of infection increase at earlier gestational ages.
  
  Section::::Outcomes.:Pre-term birth (before 37 weeks).
   The volume of amniotic fluid increases with the growth of fetus. From the 10th to the 20th week it increases from 25ml to 400ml approximately. Approximately in the 10th-11th week the breathing and swallowing of the fetus slightly decrease the amount of fluid, but neither urination nor swallowing contributes significantly to fluid quantity changes, until the 25th week, when keratinization of skin is complete. Then the relationship between fluid and fetal growth stops. It reaches a plateau of 800ml by the 28-week gestational age. The amount of fluid declines to roughly 400 ml at 42 weeks. There is about 500 cc to1L of amniotic fluid at birth.
   The nicotine in cigarette smoke constricts the blood vessels in the placenta and carbon monoxide, which is poisonous, enters the baby's bloodstream, replacing some of the valuable oxygen molecules carried by hemoglobin in the red blood cells. Moreover, because the fetus cannot breathe the smoke out, it has to wait for the placenta to clear it. These effects account for the fact that, on average, babies born to smoking mothers are usually born too early and have low birth weight (less than 2,500 grams or 5.5 pounds), making it more likely the baby will become sick or die.
  
raw_presuppositions: Babies should suffocate in the womb. Babies in the womb need to breathe.
raw_corrections: Babies are given oxygen through umbilical cord.  Babies in the womb don't need to breathe since they get oxygenated blood.