FACTORS AFFECTING BIRTHWEIGHT

Do you want a small baby? Your chance is best if you are a simple Chinese peasant girl of seventeen or less, in your first pregnancy. Do you want a large baby? You are more likely to have one if you are a white woman of the upper social stratum, thirty-five years old or more, with your tenth or eleventh child.

Many factors affect the baby’s size. Boys are usually three ounces heavier than girls. The average weight at birth of a Chinese baby is 6’/2 pounds (2958 grams); of a Negro baby, 7 pounds (3165 grams); of a white baby, Ivz pounds (3391 grams). A white girl pregnant for the first time at sixteen or younger will have a baby weighing 5 ounces less than the baby of her sister who postpones childbearing until she is thirty-five. Women in a tenth pregnancy have babies 12 ounces heavier than those in a first pregnancy; the increase is gradual, each child slightly heavier than the previous one.

Socio-Economic Factors

In addition, socio economic factors affect the weight of the newborn. Babies born to patients in the economically privileged groups average a half-pound more than those born to a less favored population sample. One reason, as brought forth in a recent study in Scotland, is that prematurity is far less common among the former. The premature rate of the most affluent tenth of the population was 4 per cent, in contrast to 8 per cent among the remaining nine-tenths. The well-to-do woman has relatively more rest and leisure, which probably contributes to diminished likelihood of premature termination of her pregnancy.

Factor of Nutrition

Then there is the matter of nutrition. Does a mother’s caloric intake during pregnancy influence b-rthweight? The question remains unsettled, but the bulk of evidence favors the conclusion that the maternal diet does not appreciably affect the size of the baby. Such a view agrees with data from animal experiments: to affect the nutrition of the fetus, the mother animal has to be starved almost to death. It is universal biologic law among vivipara (animals bearing live young) that the fetus is a true parasite and, like all true parasites, ruthless and cruel, even to the point of destroying the host in order to obtain food. If the mother’s diet is deficient in iron, she becomes anemic, but the fetal blood remains normal; and if the mother’s calcium intake is extremely low, her bones suffer, but the fetus is nevertheless born with a normal skeleton.

Factor of Heredity

Heredity plays a role in fetal size. Ordinarily parents descended from a lineage of big people breed infants of large size and those with small parents and grandparents produce babies of less than average birthweight.

Factor of Maternal Disease

Maternal illness may affect birthweight. Debilitating diseases usually eventuate in small babies, as does the complication of chronic high blood pressure. The only illness associated with babies of excessive size is maternal diabetes. The tendency of diabetics to deliver very large infants is independent of the severity of the diabetes or the degree of control of the diabetic condition. However, the woman whose diabetes is of recent origin is more likely to have a baby of excessive size than the woman whose diabetes is long standing.

All the factors listed here which affect birthweight apply to the average patient in a large series of cases; in this matter the individual is often an exception, so that the couple who, according to all rules, ought to produce a large baby may produce a small one, and vice versa. It may be said, however, that couples usually have a standard-sized term baby, so that if the first baby is large, subsequent babies are usually large, or, if the first is small, they tend to continue small.

Weight Range at Term

The only certain fact in this realm is the marked variation in the birthweight of nine-month children; any figure between five and nine pounds is likely, and between three and a half and thirteen pounds, possible.

Babies of Excessive Size

How common are very large babies, and what is the most a newborn infant can weigh?

One frequently hears of babies with birthweights over eleven pounds, and sometimes one hears of newborns much larger. Most of the latter reports must be considered apocryphal; in such cases careful investigation will usually show that the weight had been estimated by hefting the child with one hand, not by weighing it.

In 23,500 consecutive deliveries at the Johns Hopkins Hospital, 251 babies weighed over 10 pounds (1 in 93.6); 35 (1 in 542) weighed over 11 pounds; 8 (1 in 2937) weighed over 12 pounds; and 2 (1 in 11,750) weighed over 13 pounds. These two were males; the smaller, who weighed pounds, 7 ounces, was the ninth child of a thirty-four-year-old patient; and the larger—14 pounds, 4 ounces—was the seventh child of a woman of forty-four. Among 30,000 deliveries in Munich, no baby weighed over 13 pounds, 4 ounces, and the largest infant born at the New York Lying-in Hospital in 100,000 cases weighed 15 pounds.

Despite the actual rarity of such phenomena I am sure that one-third of American mothers claim the distinction of having borne twelve-, fourteen-, or even sixteen-pound babies. The first question after each birth is, ‘How is she?’; the second, ‘What is it?’ If to the third—’How much does it weigh?’—the doctor replies: ‘Seven pounds,’ jaws drop and joy is remote, but if he answers, ‘Twelve pounds,’ everyone beams. Physicians realized this long before the days of obstetrical hospitals, and since at the usual home delivery the only scale was the doctor’s hand, he found it tactful to err by three or four additional pounds.

World’s Biggest Newborn

The world’s record for the largest baby is claimed by Sale City, Georgia, where in February 1916 Dr. D. P. Belcher attended Mrs. Rowe when she bore a stillborn female weighing 25 pounds. The physician failed to stipulate the type of scale or its condition. The largest baby with carefully verified weight was delivered at a hospital in Aldershot, England, and reported in 1933 by Dr. Moss in the British Medical Journal. The woman, twenty-two years old, had had one previous baby, which weighed 10 pounds. Both she and her husband were six feet tall. In this pregnancy, five days before the calculated confinement date, she gave birth to a baby weighing 24 pounds, 2 ounces. The newborn was 35 inches long—heavier and taller than the average child at one year. It was born dead. According to medical literature, no child has ever been born alive weighing more than 15.5 pounds, although the modern free usage of Cesarean section should make such a live birth not only possible but likely.