The size of the baby is affected by race, colored babies, for example, averaging a smaller weight than white babies. And, as might be expected, the size of the parents is likely to be reflected in the size of their infants, large parents tending to have large children and vice versa. The number of children which the mother has previously borne is also a factor, since the first child is usually the smallest, the size of those following showing an increase with the mother’s age up to her twenty-eighth or thirtieth year, provided the successive pregnancies do not occur at too frequent intervals. The expectant mother’s general state of health, her state of nutrition, the character of her surroundings and her mode of living may be expected to influence her baby’s welfare. Hence, women who live in comfortable, or luxurious circumstances usually have more robust babies than those who are run down, poorly nourished or overworked. All of which hints at the great value of prenatal care which will be taken up in detail in a later chapter. [Illustration: FIG. 27.—Full term fetus in utero. Drawn by Max Brodel. (Used by permission of A. J. Nystrom & Co., Chicago.) ] =A multiple pregnancy= is one in which the pregnant uterus contains two or more embryos, these being termed twins when there are two and triplets when there are three; quadruplets, quintuplets and sextuplets when there are four, five and six embryos, respectively, six being the largest accredited number on record. The tendency to multiple pregnancies is apparently inherited, and it sometimes happens that several members of the same family connection have this predisposition, as evidenced by the number of twins and triplets to be found among relatives. It is estimated that twins occur once in 90 pregnancies and triplets once in about 7000 cases. Twin pregnancies may result from the fertilization of one or of two ova, and are designated as single ovum or double ovum twins respectively. In single ovum twins the egg becomes divided early in its development and two embryos are formed. In such a case there is one placenta, one chorion and two amnions and the babies are of the same sex. In double ovum twins two ova are fertilized; both may come from the same ovary or there may be one from each side. When double ovum twins occur, there are two placentæ, as a rule, though they may be somewhat fused; two amnions and two chorions and the babies may be of the same sex or each of a different sex. Twins are often prematurely born and each one is likely to be smaller than a baby resulting from a single pregnancy, but their combined weight is greater than that of one normal baby.