By: T. Berry Brazelton, M.D., and Joshua Sparrow, M.D.

Q. Please help. I am trying to find information on the causes of my grandchild’s low birth weight. She was full term and weighed 4 pounds 7 ounces. I am concerned about the consequences for her growth and development.

Should my daughter be concerned about the outcome of future pregnancies?

A. There are many causes for low birth weight. Some may predict future pregnancies resulting in low birth weight babies, or at least suggest some increased risk for more small babies, while others may be more likely to be once-only occurrences.

Among the possible causes: cigarette smoking during pregnancy, elevated blood pressure, problems with the placenta (which brings nutrition to the fetus’ blood stream from the mother’s), and inadequate maternal weight gain during pregnancy.

The impact of a mother’s health on her pregnancy and her baby’s future is one reason why prenatal care is so important. High blood pressure can develop for the first time during pregnancy in women with no prior history of it, and can be effectively treated, so blood pressure monitoring is a cornerstone of prenatal care.

But since some health issues are evident before a pregnancy and will take more than nine months to address, access to health care for all women of childbearing age is critical for healthy pregnancies and healthy babies.

It will also save a bundle in health care and educational expenses that many premature and very low birth weight babies will need. Six billion dollars per year of our health care costs are spent on neonatal intensive care for premature infants, to say nothing of the costs for special education and other services that premature infants are more likely to need later on. A health care system that fails to care for all women of childbearing age will cost us all more in the long run.

Significant stress during pregnancy has been found to be associated with premature births, and may also be associated with low birth weight in full-term babies since stress in the expectant mother can increase her stress hormones, which in turn can constrict the uterine artery which supplies nutrients through the placenta to the fetus.

A recent study found that mothers who took time off during the last three months of pregnancy were less likely to have premature babies. With only three months of unpaid maternity leave, few working expectant mothers can afford this luxury. Paid maternity leave during the last trimester could reduce the risks – and the costs – of prematurity and low birth weight.

Your daughter’s obstetrician may be able to tell her whether there was any evidence of problems with the placenta or other troubles during this pregnancy, and whether they are of the sort that might be more likely to occur again.

The pediatrician may also be able to help out here. A baby’s length in proportion to her weight may indicate whether low weight is more likely a result of a placental problem late in pregnancy or, instead, whether genetic or other less common causes are involved.

A long, skinny baby (normal length, low weight) is more likely to be the result of a problem with the placenta late in pregnancy: Often they look wizened and worried, and may be irritable and more difficult to soothe. A very “small all over” baby (low weight and length) may have experienced a problem earlier in the pregnancy, for example an infection, or again a problem with the placenta beginning earlier on.

Genetics may also play a role – especially in a baby whose height and weight are low – as a cause for a disorder in the child of which low birth weight is only one feature. In this case there would be other, more specific signs of such a disorder as well. Your daughter can ask the baby’s pediatrician if the low birth weight is a standalone issue or part of a larger syndrome.

As for these and other possible causes of concern for a low birth weight baby’s growth and development, we would hate to see you and your daughter worry about all the possibilities and would instead urge you to ask the pediatrician to review the pregnancy with the obstetrician, and then to watch carefully over her growth and development with you.

If your daughter’s pregnancy was entirely normal and your grandchild is entirely healthy, then chances are good that her growth and development will proceed normally too. But urge the pediatrician to follow closely. Let him or her know that if the baby does need help catching up, you all are ready to get going, the sooner the better.

You may be concerned about the “fetal programming” hypothesis put forward by David Barker which states that conditions during pregnancy can have lifelong effects for the fetus’ future health, and correlates low birth weight due to malnutrition during pregnancy with future health problems. However, it is important to remember that research like Barker’s examines statistical probabilities for very large population samples, and can’t really tell you much about your grandchild. These large studies that predict the chance of one outcome or another in large groups of people can’t tell us which way the coin will flip for any single individual.

Fortunately, you are there to vigilantly watch over this baby’s growth and development, and to help your daughter respond if the pediatrician finds any cause for concern.

Development is such a powerful force, especially in the first years of life. The human brain never again grows and changes as dramatically as it does in infants. In this period it is remarkably adaptive, developing new circuits and pathways to bypass and overcome specific areas that are not able to keep up.

Early intervention – before a child turns 3 years of age – provided by specially trained professionals (speech and language therapists, occupational therapists and physical therapists, for example) can help make the most of the astounding capacity of the very young human brain to recover and grow.

Responses to questions are not intended to constitute or to take the place of medical or psychiatric evaluation, diagnosis or treatment. If you have a question about your child’s health or well-being, consult your child’s health-care provider.

Dr. Brazelton, prior to his passing, was the founder and head of the Brazelton Touchpoints Center, which promotes and supports community initiatives that are collaborative, strength-based, prevention-focused sources of support for families raising children in our increasingly stressful world. Dr. Sparrow, a child psychiatrist, is currently the Director of the Brazelton Touchpoints Center. Learn more about the Center at

Reprinted with permission from the authors.