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Few sights are more distressing to a midwife than that of an unresponsive newborn. But this was the situation Judith Mercer, a certified nurse-midwife, was facing when she assisted in a home birth in 1979. As she stared at the pale and lifeless little boy, she was terrified that she wouldn't be able to resuscitate him. She tried to stimulate him with her fingers, but he did not respond. She looked down at the umbilical cord, which connected the baby directly to his mother's placenta, and saw that it was pulsating—still delivering blood to the boy's body. His color was returning ever so slowly. A minute and a half later, the little boy opened his eyes and took a quiet breath. He did not even cry. The still-attached umbilical cord, Mercer realized, had seemingly saved this boy's life by pumping blood and oxygen—life, basically—from his mother's body to his own.
Cutting the umbilical cord. Babies are born attached to their mothers by the umbilical cord, which delivers nutrients and oxygen throughout pregnancy. After birth, the cord is clamped near the baby's navel and then cut. Delaying cord clamping by a minute or two may improve a baby's iron stores.
Mercer was awed by what she had seen. She vowed, right then and there, to study what she had witnessed and understand why and how the umbilical cord might have saved that baby boy. "That baby affected the whole second half of my lifetime," she says. Mercer went back to school and got a PhD, and as a clinical professor of nursing at the University of Rhode Island, she has dedicated her life to studying the benefits of what is known as delayed cord clamping. Until recently, it was common practice that within seconds of a birth, obstetrical care providers clamp the umbilical cord connecting mother to baby, severing the blood flow between them. As Mercer's research has shown and supported, delaying the clamping of the umbilical cord by at least 1 minute can provide benefits. The cord not only continues to provide blood and oxygen to the newborn but also increases the baby's hemoglobin levels at birth and improves stores of iron in the first months of life.
In March 2013, the Cochrane Collaboration, a nonprofit international consortium funded in part by the U.S. Department of Health and Human Services, analyzed the results of 15 clinical trials—many conducted by Mercer—and concluded that delayed clamping increases birth weight (by increasing the newborn's blood volume) and halves the risk that babies will be iron-deficient when they are three to six months old. (Iron deficiency is a risk factor for future cognitive problems.) At that time, few healthcare providers who delivered babies delayed the clamping of umbilical cords, in part because it took extra time and in part because delaying clamping slightly increases the risk for newborn jaundice, characterized by slight yellowing of the skin and whites of the eyes. Jaundice occurs when a product of hemoglobin breakdown, called bilirubin, accumulates in the blood. Its production is a normal occurrence as damaged red blood cells are removed from circulation and destroyed. However, when the baby's liver has trouble processing the bilirubin, it cannot be effectively excreted in stool, causing it to accumulate in the blood. The condition, however, can usually be treated with ultraviolet light therapy and rarely causes complications.
With mounting scientific evidence and almost forty years after Mercer's initial experience, the American College of Obstetricians and Gynecologists (ACOG) issued an expert Committee Opinion in 2017 that recommended a delay in umbilical cord clamping for at least 30-60 seconds after birth—an increase over previous practice of clamping the cord after about 15-20 seconds following birth. The recommendation to delay umbilical cord clamping to no earlier than 1 minute after birth was echoed by the World Health Organization. Mercer's continued research has shown that benefits of delayed cord clamping by several minutes appears to be especially advantageous for preterm infants (born three or more weeks before their due date).

Although Mercer's research emphasizes the importance of the umbilical cord after birth, the umbilical cord's primary function is to transport nutrients and oxygen to a developing baby during pregnancy, the period from fertilization to birth. Pregnancy begins when a woman's egg is fertilized by a sperm, forming a zygote that develops into an embryo and then a fetus. Starting about four weeks after fertilization, the umbilical cord begins to develop.
The embryo, and later the fetus, is carried in a fluid-filled amniotic (membranous) sac in the muscular organ known as the uterus. The umbilical cord connects the embryo or fetus to the placenta, an organ attached to the uterus that supplies oxygen and nutrients to the developing baby and processes the waste products for elimination through the mother's bloodstream. After birth, the umbilical cord is clamped and severed. (INFOGRAPHIC E.1)
Once a woman is pregnant, her body makes gradual yet significant changes to support the growth of the fetus, and this shift alters the woman's nutritional needs. One key change is that her heart works harder and pumps more blood throughout her body—her blood volume typically increases by about 50%—and her breathing rate increases. In addition, gastrointestinal motility decreases, slowing the passage of food and potentially causing constipation, a common complaint during pregnancy.
A woman's metabolic rate increases during pregnancy, and subsequent energy demands increase to compensate. Between 5% and 20% of the increase in energy need is due to the oxygen demands of the developing fetus and maternal support tissues. Over the course of the pregnancy, there is a shift in fuel utilization by the mother to meet these increased energy requirements. Because the fetus is dependent on glucose as its primary fuel source, the mother's body relies more heavily on fatty acids to fuel her own needs. This conserves glucose so that more can be transferred to the fetus to meets this specific fuel requirement and supply its energy needs.
Women need extra food and nutrients to help their babies grow. However, more than half of all women are overweight (defined as a body mass index, or BMI, over 25) or obese (a BMI over 30) when they become pregnant. Still others gain too much weight during pregnancy—both of which can put the mother and baby's health at risk, according to recent research.
Typically, a pregnant woman only needs to start consuming more calories after the first trimester, because early in pregnancy, the developing fetus is comparatively small in relation to the mother's body mass. In general, in the second and third trimesters, pregnant women need between 2200 and 2900 total calories a day; the exact number depends on prepregnancy weight and the mother's activity level. Pregnant women should increase their caloric intake gradually, emphasizing nutrient-dense foods. Ideally, to meet increased energy demands, they should eat on average an extra 340 calories per day in the second trimester and an extra 450 calories per day in the third trimester. Underweight women need even more calories, because they must gain weight to meet the energy demands of pregnancy. Conversely, overweight women need fewer added calories during their pregnancy. Physically active women require more calories to offset energy expenditure.
One excellent resource for pregnancy meal planning is the Health and Nutrition Information for pregnant and breastfeeding women on the U.S. Department of Agriculture (USDA) website. It provides a personalized daily food plan based on age, height, weight, physical activity level, and stage of pregnancy or breastfeeding status. That said, a better way to gauge appropriate food intake is to monitor weight gain during pregnancy rather than to count daily calories. Appropriate weight gain across the course of pregnancy would indicate that energy intake is sufficient to meet the increased energy demands of pregnancy. (INFOGRAPHIC E.5)
Nutrients Needed in Increased Amounts
Ultimately, pregnant women need only an average of 15% more total calories than nonpregnant women but about 50% more of some nutrients such as protein, folate, zinc, iodine, and iron. Pregnant women can meet most of their nutritional requirements through food; in fact, the only nutrient for which a supplement is universally recommended is iron. However, prenatal multivitamin/mineral supplements are often recommended for pregnant women who may not consume adequate amounts of vitamins and minerals in their diet or for those who have high-risk pregnancies. Pregnant women who are vegans should also take supplemental vitamin D, iron, and vitamin B12 to ensure adequate intake of these nutrients. When choosing supplements, however, pregnant women should be careful to follow the advice of their doctor or midwife and not buy products that contain more than the recommended intake of any nutrient, as doing so could cause toxicity. (Refer to Spotlight D for more on dietary supplementation.)
Folate (the synthetic form of which is called folic acid), a water-soluble B vitamin, is one of the key nutrients that mothers-to-be need before and during pregnancy, as it is crucial for the development of new cells. Folate deficiency is associated with fetal growth problems, birth defects, schizophrenia, and autism. In addition, women who don't get enough folate during the first 12 weeks of pregnancy are up to 70% more likely to give birth to babies with neural tube defects such as spina bifida.
Spina bifida is linked to insufficient folic acid in a mother's diet. Spina bifida is a neural tube defect—a disorder involving incomplete development of the brain, spinal cord, and/or their protective coverings. It occurs when the fetus's spine fails to close properly during the first month of pregnancy.
The U.S. Centers for Disease Control and Prevention (CDC) recommends that all women between the ages of 15 and 45 years—even if they are not pregnant—consume a daily dose of 400 micrograms of folic acid in a multivitamin or the equivalent through folate-rich foods. This recommendation applies to all women of child-bearing age because half of U.S. pregnancies are unplanned, and birth defects from folate deficiency develop as early as three to four weeks into pregnancy, before most women even know they are pregnant. During pregnancy, women should consume the equivalent of 600 micrograms of folate daily from foods or supplements. To help women meet these requirements, in 1998, the U.S. Food and Drug Administration began requiring food manufacturers to add folic acid to common grain products such as breads, cereals, flours, and pastas.
Some women have trouble getting the nutrients they need because they suffer from morning sickness, triggered by hormonal changes that can cause nausea and vomiting in the first trimester and may sometimes cause unique food aversions. They are also at a heightened risk for pica, an eating disorder that causes individuals to want to ingest nonfood substances such as clay, paint chips, paste, plaster, dirt, or hair. Pica may be a sign of anemia.
With new diagnostic criteria and increasing rates of obesity, it is estimated that as many as 18% of pregnant women may develop gestational diabetes, which is characterized by elevated levels of blood glucose that pass to the fetus, causing it to be large for gestational age and thereby increasing the risk of complications to both mother and newborn. Although gestational diabetes generally resolves after pregnancy, it increases the risk that the mother will develop type 2 diabetes later in life. (Refer to Spotlight A for more on gestational diabetes.)
Preeclampsia is another condition that may affect as many as 1 in 20 women during the latter part of their pregnancies. Characterized by a sudden increase in blood pressure (hypertension) as well as protein in the urine, preeclampsia may initially result in fluid retention and swelling in the feet, ankles, hands, and face. Although the exact cause is unknown, women who gain excessive body weight during pregnancy or those with existing hypertension, diabetes, or obesity prior to pregnancy are at higher risk for developing preeclampsia. As with gestational diabetes, preeclampsia does not resolve until delivery. With diagnosis, monitoring, and treatment, the risk of complications and consequences for both the mother and developing baby can be reduced. Adequate hydration, a healthy diet, and regular exercise may help reduce risk of developing preeclampsia.
Pregnant women should also avoid alcohol. Fetal alcohol syndrome is a group of conditions causing physical, behavioral, and learning problems in children whose mothers drank heavily during pregnancy. Alcohol consumed by a woman during pregnancy travels through her blood and into the baby's blood, tissues, and organs, where it breaks down slowly, exposing the fetus to the alcohol for long periods. The CDC says that there is no safe level of alcohol consumption during pregnancy.
Individuals exposed to alcohol in the womb may suffer lifelong effects. The effects of alcohol on a developing fetus can have profound consequences, including growth problems, brain damage, learning disabilities, physical abnormalities, and behavior issues.
Although caffeine is not nearly as dangerous as alcohol, a healthcare provider might recommend limiting the amount of caffeine consumed during pregnancy because it crosses the placenta into the bloodstream of a developing baby. Although most studies report no adverse effects of maternal caffeine consumption on the infant, there is some evidence that high intakes of caffeine are associated with an increased likelihood of SGA births, miscarriage, and childhood acute leukemia. The World Health Organization recommends a maternal caffeine intake of below 300 mg per day, and the American College of Obstetricians and Gynecologists recommends less than 200 mg per day. Brewed coffee contains about 135 mg per 8-ounce cup, and caffeine-containing soft drinks generally contain between 40-50 mg per 12-ounce can. Smoking—although not a nutritional issue per se—should be discontinued during pregnancy because it increases the risk of miscarriage, puts the baby at risk of premature and SGA birth, and increases the chance of infant mortality.
Pregnant women need to be careful to avoid microbial-contaminated foods. Hormonal changes during pregnancy suppress the immune system of the mother. Although such changes are necessary for the survival of the fetus, they increase the chance of foodborne infections. Pregnant women are about 20 times more likely to develop listeriosis than a nonpregnant individual. Listeriosis is a serious infection caused by eating food tainted with the bacterium Listeria monocytogenes, which can cause premature birth, miscarriage, fetal death, and newborn illness because the bacteria can cross the placenta. To minimize their risk of listeriosis, expecting women should not eat hot dogs or other luncheon meats unless they have been heated to steaming hot. They should also avoid unpasteurized cheeses such as brie, blue cheeses, camembert, and some fetas; uncooked refrigerated smoked seafood; refrigerated meat spreads and pâtés; and unpasteurized milks and juices. Campylobacter jejuni is another bacterium that can cross the placenta and cause early termination of pregnancy by the body (spontaneous abortion) and stillbirth. Raw poultry is nearly always contaminated with it, so it is important to adequately cook poultry and avoid cross-contaminating foods that will be eaten raw with drippings from uncooked poultry.
Foodborne infections are discussed further in Spotlight H Food Safety.
Pregnant women and nursing mothers should also be careful to avoid consuming mercury as it can severely impair brain development of the fetus and of children. Because seafood is the primary source of mercury in the diet, pregnant and nursing women are advised to select fish that have low levels of mercury contamination. (INFOGRAPHIC E.6)INFOGRAPHIC E.6 Food Safety during Pregnancy During pregnancy, a woman's immune system is suppressed, placing her at increased risk of contracting a foodborne illness. In some cases, these infections and toxins in foods can place either mom or the fetus at risk of severe complications.
Composition of Breast Milk
The composition of breast milk varies depending on the stage of lactation, milk volume, feeding frequency, and differences among women. The first form of milk that is produced is called colostrum, which is produced for about five days after birth. It is thick and yellowish and contains higher amounts of protein and critical antibodies than mature milk does. Once lactation is established, the primary components of mature breast milk are water (87%), carbohydrates, fats, proteins, vitamins, and minerals. At the beginning of the feeding, the milk, called foremilk, contains mostly lactose and proteins and only a little fat. The end of the feeding produces hindmilk. The hindmilk contains more fat, the main source of energy for the infant. Both foremilk and hindmilk are nutritious, but hindmilk has more calories. Despite the differences in breast milk composition, babies will be more satiated if they get both foremilk and hindmilk during feedings.
Breast milk is the ideal infant food. It provides babies with many crucial nutrients as well as antibodies that enhance their ability to fight infections and strengthen their immune systems. Breast milk is rich in vitamins, is full of essential fatty acids for brain development, contains the appropriate balance of proteins and minerals to enhance digestion, and promotes infant oral motor development. In addition, breastfeeding also reduces the risk of diarrhea and vomiting in infants and mitigates their risk of becoming obese later in life. There is also limited evidence that it may reduce the risk for chronic diseases later in life, such as type 2 diabetes and heart disease.
There are also documented benefits to breastfeeding, including reductions in incidence of upper respiratory infections during the first two years of life, in childhood leukemia, in sudden infant death syndrome, and in orthodontic problems. Evidence also exists to support higher IQ scores among children who were breastfed for at least six months. Also, breastfeeding is convenient and less expensive than formula feeding and it plays an essential role in promoting mother-infant bonding. There are added benefits for mothers who nurse that include a reduced risk of ovarian and breast cancer, less risk of developing type 2 diabetes, and possibly a faster return to prepregnancy body weight. (INFOGRAPHIC E.8)
Babies don't get all of their nutrients through breast milk alone. Parents are advised to supplement their breastfed babies with 400 IU of vitamin D each day, starting from the first few days of life. Breastfed babies of vegan or vitamin B12-deficient mothers may also require vitamin B12 supplements. All newborns are also typically given an injection of vitamin K in the hospital after birth. Babies have very little vitamin K, an important blood-clotting vitamin, in their bodies because it crosses the placenta poorly to the developing baby. In addition, although it has recently been recognized that the unborn infant's gut may contain low levels of certain bacteria that synthesize vitamin K, very little of the vitamin is absorbed from the colon where these bacteria reside.
Infants vary considerably in terms of their growth, development, nutritional needs, and feeding patterns. During the first two to six weeks of their lives, they primarily feed, sleep, and grow. By late infancy, newborn reflexes have gone away and a baby has mastered certain physical tasks that allow him or her to progress from a diet of exclusive breast milk or formula to foods with an increasingly wide variety of flavors and textures. The ways parents feed their babies not only nourish them but also help to promote motor development and establish key feeding skills, healthy habits, and strong family relationships.
Babies grow at different rates because of differing genetic factors and prenatal history, but growth is also an important indicator of adequate nutrition. Inadequate intake of calories or essential nutrients can significantly affect mental and physical development, particularly during the critical periods from birth to one year. Infants should double their birth weight by four to six months and typically triple it by their first birthday. They also grow in length by approximately 50% in their first year. (INFOGRAPHIC E.10)
Iron Needs in Infancy
Following a healthy pregnancy, most—but not all—infants have iron stores to help meet their needs until around four months of age, after which the risk for iron deficiency increases. Iron is necessary for the formation of brain cells, so iron deficiency can hinder psychomotor development. Research suggests that treating young children once they have iron deficiencies is not enough—it does not prevent cognitive problems—so it may be more important to prevent iron deficiency from developing in the first place. Babies at the highest risk for iron deficiency are those who were born prematurely, who are fed formula that is not fortified with iron, and who are exclusively breastfed without iron supplements. Because of the risks, doctors recommend that parents begin feeding their infants iron supplements after the age of four months if babies are not being fed iron-fortified complementary foods such as rice cereal.

Because iron deficiency during pregnancy and in infants is so common and so difficult to prevent without supplementation and because it can impair cognitive development, the case for delayed cord clamping is strong. "We can affect their health throughout their lifespan," Judith Mercer says. To date, six studies have confirmed that when doctors or midwives delay the clamping of the umbilical cord by 2 to 3 minutes, an infant's risk of iron deficiency at the age of four to six months drops significantly. It's possible then that by allowing blood and iron to pass from mother to child right after birth, a mother can give her baby one more gift before they are physically separated. Yet obstetrical care providers say that the practice is still not the norm and that umbilical cords are typically clamped immediately after birth unless a parent specifically requests otherwise.
Mercer is convinced of the universal benefits of delayed cord clamping. And the practice is not only gaining acceptance but also gaining endorsement by some obstetric health organizations due, in part, to her work and advocacy. It could be a while before all obstetrical practitioners change their routine practice, however, so Mercer plans to continue designing, conducting, and publishing studies in the hopes of turning the medical tide. She will also have to prove that the benefits of delayed cord clamping outweigh any potential risks.
During the 38-42 weeks of pregnancy, the developing embryo or fetus is supplied with nutrients and oxygen from the mother's placenta, which is attached to her uterus. The nutrients and oxygen are transported from the placenta to the fetus through the umbilical cord.
A woman's nutrient and energy needs change during pregnancy to support growth of the developing embryo or fetus and maternal support tissues.
A woman's energy needs gradually increase as pregnancy advances, with an average increase of 15%. Nutrient needs increase by as much as 50% for some vitamins and minerals.
The Health and Medicine Division of the National Academies of Sciences, Engineering, and Medicine provides guidelines for appropriate weight gain during pregnancy based on BMI at conception to reduce complications during pregnancy and at delivery as well as to promote a healthy birth weight for the baby.
Birth weight is influenced by several factors. Infants who are born preterm or are small for gestational age have increased risk of death, complications, and certain medical conditions as adults.
Insufficient intake of essential nutrients can increase the risk of birth defects, particularly during critical periods of accelerated embryonic or fetal development.
Folate plays an important role in the prevention of neural tube defects.
Iron needs are increased by 50% during pregnancy, which often warrants supplementation to prevent iron-deficiency anemia that affects oxygen supply and iron status of the embryo or fetus.
Potential nutrition-related complications during pregnancy include morning sickness, pica, gestational diabetes, and preeclampsia.
To reduce risks to the developing embryo or fetus, pregnant women are advised to avoid alcohol, limit their intake of certain fish because of potential mercury contamination, and avoid microbial-contaminated foods.
The American Academy of Pediatrics recommends that mothers exclusively breastfeed their babies through six months of age and then continue breastfeeding (ideally to one year or beyond) while also introducing complementary solid foods according to the infant's developmental readiness.
Breastfeeding supplies the growing infant with essential nutrients in appropriate proportions, provides antibodies to strengthen immunity, and has many additional benefits for both the mother and baby.
Breast milk may not supply sufficient vitamin D; therefore, supplementation for breastfed infants is recommended. Infants who are exclusively breastfed after six months of age may require iron supplementation.
Women who are breastfeeding have increased energy and nutrient needs for producing milk as well as replenishing nutrient stores.
Infants develop rapidly in the first year of life and require a consistent supply of energy and essential nutrients. Growth is an important indicator of adequate nutrition.