Birth weight is an important statistic -- it's right there on the announcements next to name, length, date and time of birth. It's also important from a medical standpoint, although of course there's a wide range of what's "normal" and what's low. A baby is considered to be of low birth weight if he or she weighs less than 5 pounds, 8 ounces (2,500 grams) at 37 weeks. Some babies are just small and don't have any problems associated with their size, but others have low birth weights because they experienced intrauterine growth restriction (IGR) -- they didn't get adequate nutrition while in the womb. Babies with low birth weight are at greater risk for health problems like hypoglycemia (low blood sugar) and must be closely monitored to ensure that they are growing at a normal rate.
A baby can have IGR even if the mother ate adequately while pregnant. Stress hormones such as epinephrine, norepinephrine and cortisol can all cause blood vessels to constrict, and this potentially includes the blood flow to the baby via the umbilical cord. In this case, the fetus may not be absorbing enough nutrients from the mother's body. Often, the potential for low birth weight is identified in utero, and your doctor can suggest ways to change the behaviors that may be causing it -- such as cutting down on your stress levels.
Next, we'll look at how stress can increase the risk of infection during a pregnancy.