More Sex, Even On "Off" Days, Increases Chances Of Pregnancy

Most of the miscarriages in this study occurred so soon that couples would not have even known they were pregnant if they had not been using pregnancy detection devices. Cutting way back on caffeine reduces the risk of miscarriage, but what can couples do to increase their chances of getting pregnant? The answer, not entirely intuitively, is to have more sex.

There is a very basic reason that "more sex" isn't usually a ticket for having more pregnancies. Women are only pregnant for 12 to 36 hours during the monthly periods. The fallopian tubes release an egg (or sometimes multiple eggs) after ovulation, and the egg has to be fertilized right away or it deteriorates. It isn't enough to have sex right at the moment the egg leaves the fallopian tube. Sperm have to be on their way shortly before ovulation. It can take several days for sperm to swim through cervical fluids into the uterus, and the consistency of cervical fluid has an influence on how fast the sperm arrive. Some sperm are better swimmers than others, and only one sperm fertilizes the egg, but if timing is a little off, then the woman is not fertile again until a similar point in her next menstrual cycle. Sex on other days shouldn't "count," except that recent research indicates that it does.

Dr. Tierney Lorenz, a visiting research scientist at the Kinsey Institute at Indiana University, notes that women who have more sex are more likely to get pregnant, even when they are having sex on days that they are not fertile. Why should this be? Dr. Lorenz and her colleagues believe that it has to do with the immune system. In a study of 32 women, Dr. Lorenz and her colleagues found that sexual activity changes the way a woman's body produces helper T cells.

These specialized white blood cells fight infection, but not all helper T cells fight infection in the same way. There are type 1 and type 2 helper T cells. The different kinds of helper T cells release different kinds of interleukins in response to microbes that enter the human body. Type 1 helper T cells attack bacteria. Type 2 helper T cells attack parasites. 

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When women have more sex, their bodies make more type 1 helper T cells. Their bodies are more attuned to fighting infections of a sort that are more likely to cause problems during pregnancy. When women have less sex, their bodies make more type 2 helper T cells. Their bodies are attuned to fighting microorganisms, perhaps even including the embryo, than fighting bacteria infections. Having more sex prepares the uterus to fight infections but to welcome the embryo.

A woman's body has to defend itself against infection but welcome sperm and the fertilized egg. The more sex a woman has, the more ready she will be for pregnancy.