New research dispels the popularly held belief that having sex in the last few weeks of pregnancy speeds the baby's arrival. In fact, the study found the opposite to be true; women who abstained from sex delivered earlier than those who did not. The results were published in the June issue of the journal Obstetrics & Gynecology

Researchers from Ohio State University Medical Center studied 93 pregnant women, about half of whom engaged in sex during the final three weeks of their pregnancy. During successive doctor's visits, the women underwent cervical examinations and reported how many times they had had intercourse in the previous week.

The researchers found no connection between the amount of sex a pregnant woman had and the degree of "ripening" of her cervix (a measure of how close she is to delivering the baby). Overall, women who were sexually active delivered significantly later (average of 39.9 weeks) than women who abstained from sex (average of 39.3 weeks).

Jonathan Schaffir, M.D., lead author and an obstetrician at Ohio State Medical Center, tried to make sense of these findings. Dr. Schaffir speculated that women who experience pain or pressure in their pelvis and abdomen—potential signs that they are nearing delivery—may be abstaining from sex. Women who are more comfortable late in their pregnancy might be more sexually active.

While more research will be needed to figure out why sexual activity may be linked to a delayed birth, Dr. Schiffer concluded that having sex late into a pregnancy does not induce labor. "Patients may continue to hear the 'old wives' tale' that intercourse will hasten labor," Dr. Schiffer said, "But according to this data, they should not hear it from the medical community."