"In the last several decades, there have been several studies looking at the link between sperm and recurring miscarriage, but nobody actually found a correlation -- mainly because they were only looking at general semen analysis," says the study's author, Dr. Harry Hatasaka, medical director of the Utah Center for Reproductive Medicine at the University of Utah.
"As far as I know, this was one of the first studies to look at the genetic side of things in much more detail," Hatasaka adds, "which is why, I believe, the correlation has finally been made."
Whether occurring just one time or repeatedly, the majority of miscarriages are caused by chromosomal abnormalities -- genetic defects within the embryo that affect its ability to thrive. In the past, it was believed that only a defective egg could lead to this event.
More recently, however, experts have come to believe that a defective sperm may also contribute to faulty conception, and in doing so become a cause of miscarriage. But doctors say this study was the first to prove it can happen.
"It is something we always suspected, but now this is one of the strongest pieces of information we have to indicate that it is a definite possibility in a subgroup of patients -- and the study adds an important dimension to the investigation of what is behind a couple's recurring pregnancy losses," says Dr. Peter Schlegel, acting chairman of urology at New York Presbyterian at Weill Cornell Medical Center in New York City.
Indeed, Schlegel says, preliminary information shows that sperm abnormalities can play a significant role in either getting pregnant or maintaining a pregnancy. This study, he says, adds to this growing body of knowledge.
The new study, published in the June issue of Obstetrics and Gynecology, focused on a small group of just 24 men, whose partners all had at least one unexplained pregnancy loss. According to Hatasaka, all of the women underwent what he says was "state of the art testing," including genetic screenings, and were found to be normal.
To check the men, researchers obtained semen samples from each partner, along with samples from 26 sperm donors with a history of at least one successful pregnancy within the previous two years. Sperm was also collected from a general population of 42 men. The age range for all the men in the study was between 26 and 36.
After the samples were retrieved, the semen was liquefied, isolated and then subjected to a series of highly detailed tests. This included checking for motility (the ability of the sperm to move or swim), concentration (the number of sperm in a selected sample), viability (general health), morphology (form, structure and genetic material), plus the way the sperm would react in fluids that approximate what is found in the female reproductive system.
"We were primarily looking for evidence of breaks in the DNA that would indicate a genetic defect that would result in a defected embryo, which would eventually result in pregnancy loss," Hatasaka says.
The result: While some of the tests showed similar results among all the men, in those whose partners had a history of miscarriage, researchers identified some specific differences, including the presence of chromosomal abnormalities.
"Even though it may not manifest in a simple semen analysis, this study shows that there must be some genetic defect that halts the process of embryogenisis [the creation of life] at some point and leads to recurrent pregnancy loss," Hatasaka says.
The good news is that "at least some potential causes of abnormal sperm are treatable conditions that might also increase pregnancy odds," Schlegel says.
Hatasaka adds that environmental factors, particularly cigarette smoke, can cause some of the cell changes capable of altering the DNA, resulting in the kind of genetic breaks in the sperm that are now linked to miscarriage.
"If your partner is having recurring miscarriages, clearly, stopping smoking might make an important difference," Hatasaka says.
Currently, there is no U.S. Food and Drug Administration test specifically approved for evaluating sperm for genetic defects linked to miscarriage.
However, experts say most major fertility centers or genetic laboratories should be able to perform the tests.
To learn more about the causes of recurrent miscarriage, check out: The American College of Obstetricians and Gynecologists. For more on male fertility, visit this page at the University of Utah School of Medicine.