What Scientists Know About the First Nine Months

What scientists have learned about those amazing first nine months--and what it means for mothers

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    PCBs are no longer manufactured in the U.S., but other chemicals potentially harmful to developing embryos and fetuses are. Theo Colborn, director of the World Wildlife Fund's contaminants program, says at least 150 chemicals pose possible risks for fetal development, and some of them can interfere with the naturally occurring sex hormones critical to the development of a fetus. Antiandrogens, for example, are widely found in fungicides and plastics. One in particular--DDE, a breakdown product of ddt--has been shown to cause hypospadias in laboratory mice, a birth defect in which the urethra fails to extend to the end of the penis. In humans, however, notes Dr. Allen Wilcox, editor of the journal Epidemiology, the link between hormone-like chemicals and birth defects remains elusive.

    The list of potential threats to embryonic life is long. It includes not only what the mother eats, drinks or inhales, explains N.Y.U.'s Nathanielsz, but also the hormones that surge through her body. Pregnant rats with high blood-glucose levels (chemically induced by wiping out their insulin) give birth to female offspring that are unusually susceptible to developing gestational diabetes. These daughter rats are able to produce enough insulin to keep their blood glucose in check, says Nathanielsz, but only until they become pregnant. At that point, their glucose level soars, because their pancreases were damaged by prenatal exposure to their mother's sugar-spiked blood. The next generation of daughters is, in turn, more susceptible to gestational diabetes, and the transgenerational chain goes on.

    In similar fashion, atherosclerosis may sometimes develop because of prenatal exposure to chronically high cholesterol levels. According to Dr. Wulf Palinski, an endocrinologist at the University of California at San Diego, there appears to be a kind of metabolic memory of prenatal life that is permanently retained. In genetically similar groups of rabbits and kittens, at least, those born to mothers on fatty diets were far more likely to develop arterial plaques than those whose mothers ate lean.

    But of all the long-term health threats, maternal undernourishment--which stunts growth even when babies are born full term--may top the list. "People who are small at birth have, for life, fewer kidney cells, and so they are more likely to go into renal failure when they get sick," observes Dr. David Barker, director of the environmental epidemiology unit at England's University of Southampton. The same is true of insulin-producing cells in the pancreas, so that low-birth-weight babies stand a higher chance of developing diabetes later in life because their pancreases--where insulin is produced--have to work that much harder. Barker, whose research has linked low birth weight to heart disease, points out that undernourishment can trigger lifelong metabolic changes. In adulthood, for example, obesity may become a problem because food scarcity in prenatal life causes the body to shift the rate at which calories are turned into glucose for immediate use or stored as reservoirs of fat.

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