New research shows the low birthweight rate is not due to fertility therapy.
An increase in low birthweight births occurred in Massachusetts from 1997 to 2004, and although in vitro fertilization and other fertility therapies are associated with such births, the contribution of these treatments to the trend was minor, new research shows.
Low birthweight, defined as a weight of less than 1 500 grams (3 pounds, 5 ounces), has been tied to a higher risk of developmental and learning problems and to lower academic achievement.
For adults, low birthweight has been linked to chronic health conditions, such as high blood pressure and heart disease. Researchers suspect that poor growth in the womb may "programme" the body's metabolism and development in ways that raise the odds of cardiovascular disease.
There has been an increase in low birthweight births throughout the US in the last few decades, Dr. B. B. Cohen, from the Massachusetts Department of Public Health, and colleagues point out in the Morbidity and Mortality Weekly Report. At the same time, use of fertility therapies has also increased.
Until recently, however, information was lacking to be able to assess whether these two trends were, in fact, related to each other.
In the current study, the research team was able to link 13 025 birth certificate records to fertility therapy records from 1997 to 2004 in Massachusetts.
The results show that 2% of all births were due to fertility therapies, while 7% of all low birthweight births were attributable to such treatments.
Overall, low birthweights among babies born without the assistance of fertility therapy rose from 4.8 to 5.1% during the study period, while infants born after fertility therapy climbed from 6.4 to 8.2%. This corresponds to 407 and 59 additional low birthweight babies.
"Although (fertility therapy) contributes disproportionately to low birthweight, only a small percentage of the excess low birthweight births in Massachusetts are explained by (fertility therapy); therefore, other causes for the increase in low birthweight should be examined," the authors conclude.
They add: "Future low birthweight research and prevention efforts are needed and should include: 1) determining the risk factors that contribute to increasing rates of low birthweight among (non-fertility therapy) births, and 2) investigating additional risk factors and (causes) for low birthweight" among fertility therapy infants.