The baby's advent into the world marks epic changes for newborn and mother alike. Major fetal organs like the lungs, stomach, intestines, and kidneys, which have remained untested because there was no oxygen to breathe, food to digest, or wastes to eliminate, all must start functioning at once in some cases within seconds of delivery. Others already in use like the heart and brain must adapt without hesitation to a world for which they have been meticulously designed and prepared but that differs utterly from the one in which they've functioned. Blood coming into the heart must suddenly be shunted to the lungs, meaning the opening between the 2 upper chambers (necessary for circulation when oxygen enters the bloodstream through the placenta) needs to be sealed at once. The nervous system immediately starts making use of information from eyes practically blinded by a blizzard of incoming data (not to mention the eyedrops doctors give them to prevent infections). Returning to the idea that we are mechanical buildings, it is as if we were constructed under the ocean, then thrust up onto dry land in perfect working order - and immediately pressed into service.

A baby, unlike a fetus, must sustain itself against shocks, changes in temperature, disease; still later, against the rough and tumble of school, work, dating, loss, and having children of one's own. Starting at birth, it must negotiate for itself. Thus the days of being a parasitic dependent on an acquiescent host are (one hopes) over.

For the mother, there is a corresponding loss of primacy in the fetus' life. She has been everything – food, climate, shelter, security — literally the air her child has breathed. She was occupied by an invader, one who caused her willingly to put up with enormous discomfort and changes in herself, who is now outside her, crying out.

The “sweet sorrow” of parting may be lost on her as the shock of separation sets in. But babies, like fetuses, have a remarkable way of insinuating themselves into their parents' lives. Indeed, their helpless perfection and helplessness gives them the power, as every proud parent learns, to attract not only admirers and sympathizers, but adoring crowds.

From a fetal perspective, the process of birth is a crisis. In the womb, the fetus was snuggled in a soft, warm, dark, and quiet world. The placenta provided nutrition and oxygen continuously. Suddenly, the contractions of labor and vaginal childbirth forcibly squeeze the fetus through the birth canal, limiting oxygenated blood flow during contractions and shifting the skull bones to accommodate the small space. After birth, the newborn’s system must make drastic adjustments to a world that is colder, brighter, and louder, and where he or she will experience hunger and thirst. The neonatal period (neo- = “new”; -natal = “birth”) spans the first to the thirtieth day of life outside of the uterus.

Overview

The first breath a newborn takes at birth inflates the lungs and dramatically alters the circulatory system, closing the three shunts that directed oxygenated blood away from the lungs and liver during fetal life. Clamping and cutting the umbilical cord collapses the three umbilical blood vessels. The proximal umbilical arteries remain a part of the circulatory system, whereas the distal umbilical arteries and the umbilical vein become fibrotic. The newborn keeps warm by breaking down brown adipose tissue in the process of nonshivering thermogenesis. The first consumption of breast milk or formula floods the newborn’s sterile gastrointestinal tract with beneficial bacteria that eventually establish themselves as the bacterial flora, which aid in digestion.

Respiratory Adjustments

Although the fetus “practices” breathing by inhaling amniotic fluid in utero, there is no air in the uterus and thus no true opportunity to breathe. (There is also no need to breathe because the placenta supplies the fetus with all the oxygenated blood it needs.) During gestation, the partially collapsed lungs are filled with amniotic fluid and exhibit very little metabolic activity. Several factors stimulate newborns to take their first breath at birth. First, labor contractions temporarily constrict umbilical blood vessels, reducing oxygenated blood flow to the fetus and elevating carbon dioxide levels in the blood. High carbon dioxide levels cause acidosis and stimulate the respiratory center in the brain, triggering the newborn to take a breath.

The first breath typically is taken within 10 seconds of birth, after mucus is aspirated from the infant’s mouth and nose. The first breaths inflate the lungs to nearly full capacity and dramatically decrease lung pressure and resistance to blood flow, causing a major circulatory reconfiguration. Pulmonary alveoli open, and alveolar capillaries fill with blood. Amniotic fluid in the lungs drains or is absorbed, and the lungs immediately take over the task of the placenta, exchanging carbon dioxide for oxygen by the process of respiration.

Circulatory Adjustments

The process of clamping and cutting the umbilical cord collapses the umbilical blood vessels. In the absence of medical assistance, this occlusion would occur naturally within 20 minutes of birth because the Wharton’s jelly within the umbilical cord would swell in response to the lower temperature outside of the mother’s body, and the blood vessels would constrict. Natural occlusion has occurred when the umbilical cord is no longer pulsating. For the most part, the collapsed vessels atrophy and become fibrotic remnants, existing in the mature circulatory system as ligaments of the abdominal wall and liver. The ductus venosus degenerates to become the ligamentum venosum beneath the liver. Only the proximal sections of the two umbilical arteries remain functional, taking on the role of supplying blood to the upper part of the bladder (image).

The newborn’s first breath is vital to initiate the transition from the fetal to the neonatal circulatory pattern. Inflation of the lungs decreases blood pressure throughout the pulmonary system, as well as in the right atrium and ventricle. In response to this pressure change, the flow of blood temporarily reverses direction through the foramen ovale, moving from the left to the right atrium, and blocking the shunt with two flaps of tissue. Within 1 year, the tissue flaps usually fuse over the shunt, turning the foramen ovale into the fossa ovalis. The ductus arteriosus constricts as a result of increased oxygen concentration, and becomes the ligamentum arteriosum. Closing of the ductus arteriosus ensures that all blood pumped to the pulmonary circuit will be oxygenated by the newly functional neonatal lungs.

Thermoregulatory Adjustments

The fetus floats in warm amniotic fluid that is maintained at a temperature of approximately 98.6°F with very little fluctuation. Birth exposes newborns to a cooler environment in which they have to regulate their own body temperature. Newborns have a higher ratio of surface area to volume than adults. This means that their body has less volume throughout which to produce heat, and more surface area from which to lose heat. As a result, newborns produce heat more slowly and lose it more quickly. Newborns also have immature musculature that limits their ability to generate heat by shivering. Moreover, their nervous systems are underdeveloped, so they cannot quickly constrict superficial blood vessels in response to cold. They also have little subcutaneous fat for insulation. All these factors make it harder for newborns to maintain their body temperature.

Newborns, however, do have a special method for generating heat: nonshivering thermogenesis, which involves the breakdown of brown adipose tissue, or brown fat, which is distributed over the back, chest, and shoulders. Brown fat differs from the more familiar white fat in two ways:

• It is highly vascularized. This allows for faster delivery of oxygen, which leads to faster cellular respiration.
• It is packed with a special type of mitochondria that are able to engage in cellular respiration reactions that produce less ATP and more heat than standard cellular respiration reactions.

The breakdown of brown fat occurs automatically upon exposure to cold, so it is an important heat regulator in newborns. During fetal development, the placenta secretes inhibitors that prevent metabolism of brown adipose fat and promote its accumulation in preparation for birth.

In the minutes following birth, a newborn must undergo dramatic systemic changes to be able to survive outside the womb. An obstetrician, midwife, or nurse can estimate how well a newborn is doing by obtaining an Apgar score. The Apgar score was introduced in 1952 by the anesthesiologist Dr. Virginia Apgar as a method to assess the effects on the newborn of anesthesia given to the laboring mother. Healthcare providers now use it to assess the general wellbeing of the newborn, whether or not analgesics or anesthetics were used.

Five criteria—skin color, heart rate, reflex, muscle tone, and respiration—are assessed, and each criterion is assigned a score of 0, 1, or 2. Scores are taken at 1 minute after birth and again at 5 minutes after birth. Each time that scores are taken, the five scores are added together. High scores (out of a possible 10) indicate the baby has made the transition from the womb well, whereas lower scores indicate that the baby may be in distress.

The technique for determining an Apgar score is quick and easy, painless for the newborn, and does not require any instruments except for a stethoscope. A convenient way to remember the five scoring criteria is to apply the mnemonic APGAR, for “appearance” (skin color), “pulse” (heart rate), “grimace” (reflex), “activity” (muscle tone), and “respiration.”

Of the five Apgar criteria, heart rate and respiration are the most critical. Poor scores for either of these measurements may indicate the need for immediate medical attention to resuscitate or stabilize the newborn. In general, any score lower than 7 at the 5-minute mark indicates that medical assistance may be needed. A total score below 5 indicates an emergency situation. Normally, a newborn will get an intermediate score of 1 for some of the Apgar criteria and will progress to a 2 by the 5-minute assessment. Scores of 8 or above are normal.

Write down if you would like someone in particular, such as your partner, to cut the umbilical cord. You could also mention if you would prefer delayed cord clamping. This is where the umbilical cord is not clamped or cut until after pulsations have stopped or until after the placenta is delivered.

Delayed cord clamping is an increasingly popular practice (many services now do this routinely) because delaying the clamping of the cord can mean your newborn ends up with more blood volume than it would have if the cord had been clamped immediately.

If your baby requires emergency treatment delayed cord clamping will not be an option.

Gastrointestinal and Urinary Adjustments

In adults, the gastrointestinal tract harbors bacterial flora—trillions of bacteria that aid in digestion, produce vitamins, and protect from the invasion or replication of pathogens. In stark contrast, the fetal intestine is sterile. The first consumption of breast milk or formula floods the neonatal gastrointestinal tract with beneficial bacteria that begin to establish the bacterial flora.

The fetal kidneys filter blood and produce urine, but the neonatal kidneys are still immature and inefficient at concentrating urine. Therefore, newborns produce very dilute urine, making it particularly important for infants to obtain sufficient fluids from breast milk or formula.

Throughout the second half of gestation, the fetal intestines accumulate a tarry, greenish black meconium. The newborn’s first stools consist almost entirely of meconium; they later transition to seedy yellow stools or slightly formed tan stools as meconium is cleared and replaced with digested breast milk or formula, respectively. Unlike these later stools, meconium is sterile; it is devoid of bacteria because the fetus is in a sterile environment and has not consumed any breast milk or formula. Typically, an infant does not pass meconium until after birth. However, in 5–20 percent of births, the fetus has a bowel movement in utero, which can cause major complications in the newborn.

The passage of meconium in the uterus signals fetal distress, particularly fetal hypoxia (i.e., oxygen deprivation). This may be caused by maternal drug abuse (especially tobacco or cocaine), maternal hypertension, depletion of amniotic fluid, long labor or difficult birth, or a defect in the placenta that prevents it from delivering adequate oxygen to the fetus. Meconium passage is typically a complication of full-term or post-term newborns because it is rarely passed before 34 weeks of gestation, when the gastrointestinal system has matured and is appropriately controlled by nervous system stimuli. Fetal distress can stimulate the vagus nerve to trigger gastrointestinal peristalsis and relaxation of the anal sphincter. Notably, fetal hypoxic stress also induces a gasping reflex, increasing the likelihood that meconium will be inhaled into the fetal lungs.

Although meconium is a sterile substance, it interferes with the antibiotic properties of the amniotic fluid and makes the newborn and mother more vulnerable to bacterial infections at birth and during the perinatal period. Specifically, inflammation of the fetal membranes, inflammation of the uterine lining, or neonatal sepsis (infection in the newborn) may occur. Meconium also irritates delicate fetal skin and can cause a rash.

The first sign that a fetus has passed meconium usually does not come until childbirth, when the amniotic sac ruptures. Normal amniotic fluid is clear and watery, but amniotic fluid in which meconium has been passed is stained greenish or yellowish. Antibiotics given to the mother may reduce the incidence of maternal bacterial infections, but it is critical that meconium is aspirated from the newborn before the first breath. Under these conditions, an obstetrician will extensively aspirate the infant’s airways as soon as the head is delivered, while the rest of the infant’s body is still inside the birth canal.

Aspiration of meconium with the first breath can result in labored breathing, a barrel-shaped chest, or a low Apgar score. An obstetrician can identify meconium aspiration by listening to the lungs with a stethoscope for a coarse rattling sound. Blood gas tests and chest X-rays of the infant can confirm meconium aspiration. Inhaled meconium after birth could obstruct a newborn’s airways leading to alveolar collapse, interfere with surfactant function by stripping it from the lungs, or cause pulmonary inflammation or hypertension. Any of these complications will make the newborn much more vulnerable to pulmonary infection, including pneumonia.

At birth, your baby’s tummy can hold only about one or two teaspoons. At 1 week old, your baby’s stomach grows to hold about 2 ounces — the size of an almond. Newborns usually lose a little weight in the first few days after being born. Three to five days after coming home from the hospital, you’ll take your baby back to the doctor’s office to make sure everything is on track. Meanwhile, keep a record of your baby’s dirty diapers and feedings, so you can tell whether your baby is eating enough.

Do not give cereal to babies less than 6 months old, and don’t add formula to what your baby eats without checking with your baby’s doctor. A baby’s digestive system is still undeveloped, and breastmilk is easier to digest than formula.

Spitting up is a common occurrence for newborns and is usually not a sign of a more serious problem. After feeding, try to keep the infant calm and in an upright position for a little while. Keep a burp towel handy, just in case. Contact your health care provider immediately if your infant:

• Is not gaining weight
• Is spitting up so forcefully that stomach contents shoot out of the infant's mouth
• Spits up green or yellow liquid, blood, or a substance that looks like coffee grounds
• Has blood in the stool
• Shows other signs of illness, such as fever, diarrhea, or difficulty with breathing

Some parents worry that their infant will spit up and choke if they are put to sleep on their backs, but this is not the case. Healthy infants naturally swallow or cough up fluids—it's a reflex all people have. Where the opening to the windpipe is located in the body makes it unlikely for fluids to cause choking. Babies may actually clear such fluids better when on their backs.

The NICHD's Safe to Sleep® Campaign (formerly the Back to Sleep campaign) recommends placing infants to sleep on their backs to reduce the risk for sudden infant death syndrome (SIDS). Since the recommendation for back sleeping began in 1992, the number of fatal choking deaths has not increased. In fact, in most of the few reported cases of fatal choking, an infant was sleeping on his or her stomach.

Newborn screening is the practice of testing newborns for certain disorders and conditions in the first 24 to 48 hours after they are born. In some cases, infants seem healthy at birth, but if they have these disorders or conditions they can develop serious medical problems later in infancy or childhood.

Newborn screening helps reduce and sometimes prevent negative outcomes by identifying conditions early. This may allow treatment to begin early enough to prevent damage. Newborn screening helps infants who, not very long ago, might have died in infancy or early childhood to grow to healthy adulthood.

Jaundice can cause an infant's skin, eyes, and mouth to turn a yellowish color. The yellow color is caused by a buildup of bilirubin, a substance that is produced in the body during the normal process of breaking down old red blood cells and forming new ones.

Normally the liver removes bilirubin from the body. But, for many infants, in the first few days after birth, the liver is not yet working at its full power. As a result, the level of bilirubin in the blood gets too high, causing the infant's color to become slightly yellow—this is jaundice.

Although jaundice is common and usually not serious, in some cases, high levels of bilirubin could cause brain injury. All infants with jaundice need to be seen by a healthcare provider.

Many infants need no treatment. Their livers start to catch up quickly and begin to remove bilirubin normally, usually within a few days after birth. For some infants, healthcare providers prescribe phototherapy—a treatment using a special lamp—to help break down the bilirubin in their bodies.

If your infant has jaundice, ask your healthcare provider how long the child's jaundice should last after leaving the hospital, and schedule a follow-up appointment as directed. If the jaundice lasts longer than expected, or an infant who did not have jaundice starts to turn yellowish after going home, a healthcare provider should be consulted right away. If you intend to get discharged early, particularly within 48 hours of birth, your infant's jaundice may peak later in the first week.

It is almost impossible to say how severe the jaundice level is by just looking at the baby's skin, especially for infants of color. Therefore, make every effort to keep follow-up appointments so the healthcare provider can check the level of jaundice with a simple blood test.

Jaundice is the yellow color seen in the skin of many newborns. Jaundice happens when a chemical called bilirubin builds up in the baby’s blood. During pregnancy, the mother’s liver removes bilirubin for the baby, but after birth the baby’s liver must remove the bilirubin. In some babies, the liver might not be developed enough to efficiently get rid of bilirubin. When too much bilirubin builds up in a new baby’s body, the skin and whites of the eyes might look yellow. This yellow coloring is called jaundice.

When severe jaundice goes untreated for too long, it can cause a condition called kernicterus. Kernicterus is a type of brain damage that can result from high levels of bilirubin in a baby’s blood. It can cause athetoid cerebral palsy and hearing loss. Kernicterus also causes problems with vision and teeth and sometimes can cause intellectual disabilities. Early detection and management of jaundice can prevent kernicterus.

Within a few minutes of being born, babies will automatically look to get milk from their mother's breast. Babies don't need to learn how to latch. The challenge as a new mom is learning how to tell the difference between a baby who is hungry and one who is tired or just uncomfortable. Breastfeeding on cue will help you recognize some of your baby's hunger signs, such as lip smacking and fist gnawing. When in doubt, always offer the breast. A baby who isn't hungry won't eat. Think of breastfeeding like a dance and let your baby lead. Be patient. Keep trying. You will get it.

Babies can’t tell time. In the first few weeks, there’s no such thing as a baby “sleeping pattern” or “sleep training.” Instead, new babies go through many little bursts of being awake and asleep throughout the day and night. Often, there are just a few long stretches of sleep. During those first weeks, most of your baby’s awake time is spent feeding.

So, as long as your baby is peeing and pooping enough for at least 6 dirty diapers a day, you only need to wake your baby to feed if it’s been longer than four hours since the last feeding. If your breasts get very full, especially at night, try expressing some milk either by hand or with a breast pump. And remember to sleep when the baby sleeps. Your sleep is important too!