Want a smaller baby to deliver? Doing regular moderate-intensity workouts throughout your pregnancy could lead to a lower birth weight.

A new study by New Zealand researchers finds that women who participate in regular aerobic exercise give birth to slightly smaller babies. Researchers at the University of New Zealand studied 84 first-time mothers who were divided into two groups: one that did a maximum of 40 minutes of moderately brisk cycling a week until 36 weeks of pregnancy and one that did not exercise.

The researchers also studied the impact of exercise on a woman's insulin sensitivity.

Exercise improves insulin sensitivity and helps prevent insulin resistance, a state in which the body's cells become less sensitive to the effects of insulin, a hormone secreted by the pancreatic gland, which helps convert glucose into energy. People with insulin resistance often go on to develop conditions such as diabetes, as their insulin resistance causes their body to go into insulin overdrive.

In pregnancy, however, the opposite is true: insulin resistance ensures that the fetus receives the nutrients it needs to grow. As a result, reducing it isn't wise.

Surprisingly, the New Zealand researchers found that among the pregnant women in the study who exercised, there was almost no impact on insulin sensitivity — and there was no impact on the development of the baby. Insulin levels were measured at 19 and 34 to 35 weeks of pregnancy using an IV glucose intolerance test.

Instead, babies of women who exercised were born between 49 and 237 grams (1.7 ounces and 8.4 ounces) lighter than their non-exercising counterparts, a positive finding, say researchers, as higher birth weights have been linked to obesity in adulthood. The birth weights were measured within 48 hours of the babies' delivery.

"Given that large birth size is associated with an increased risk of obesity, a modest reduction in birth weight may have long-term health benefits for offspring by lowering this risk in later life," Paul Hofman of the University of Auckland in New Zealand and co-author of the studysaid in a release..

The study is to be published in the May issue of Journal of Clinical Endocrinology & Metabolism.