A new study links fetal birth weight to type of conception. According to the study, infants conceived using fertility treatments are significantly smaller than infants born after natural conception. The study included 1,700 women who gave birth to one child. Multiple pregnancies were not used in the study because multiple pregnancies tend to result in lower birth weight babies.

The research study revealed that women utilizing fertility treatments to conceive gave birth to infants that were roughly 1/3 of a pound lighter than women who gave birth to infants conceived naturally. The study group included about 460 women who were treated at a fertility clinic for fertility problems. The women were treated with in-vitro fertilization and fertility drugs. About 100 of the women conceived naturally, without treatment. The women in the study group were compared to just less than 1,300 women who conceived naturally without fertility problems.

Women receiving fertility treatments to help them conceive gave birth to smaller singlets compared to the natural conception group. The highest gap in birth weight appeared between the natural group and the group taking fertility drugs to get pregnant. Women taking fertility drugs to force egg release gave birth to infants weighing up to 0.5 pounds less than women conceiving naturally.

Women who take fertility drugs to conceive may have underlying fertility problems that could increase the risk of low birth weight. In the case of PCOS, for instance, women are given fertility drugs to spark egg release and increase the chance of conception. In these cases, the PCOS could contribute to lower birth weight.

Researchers also believe the length of time it takes for a woman to conceive may have something to do with birth weight. For instance, women who take longer to conceive give birth to smaller babies. Due to recent studies on the impact of birth weight and fetal health on long-term health, researchers plan to continue studying the effect of birth weight on health throughout lifespan.

Source: Amber R. Cooper, M.D., M.S.C.I., Kathleen E. O’Neill, M.D., Jenifer E. Allsworth, M.D., Emily S. Jungheim, M.D., M.S.C.I., Anthony O. Odibo, M.D., M.S.C.E., Diana L. Gray, M.D., Valerie S. Ratts, M.D., Kelle H. Moley, M.D., Randall R. Odem, M.D. Fertility and Sterility. November, 2011.