University at Buffalo (UB)
Release Date: June 2, 1998 This content is archived.
SAN DIEGO -- Fertility researchers at the University at Buffalo School of Medicine and Biomedical Sciences have found a link between specific clinical pregnancies and very low levels of two sperm abnormalities.
The two abnormalities -- premature chromosomal decondensation and premature acrosome reaction, which are overlooked in a standard semen analysis -- had never been linked to low pregnancy rates, said Lani J. Burkman, Ph.D., UB assistant professor of gynecology and obstetrics, and urology, and head of the Andrology Section of the UB Department of Gynecology-Obstetrics.
By analyzing hundreds of semen samples and comparing them with subsequent pregnancies in the couples studied, Burkman and colleagues determined that samples showing more than 14 percent premature chromosomal decondensation or more than 7 percent premature acrosome reactions had only a slim chance of leading to a pregnancy.
"We were surprised to see that these two factors related to pregnancy so clearly," said Burkman, lead researcher on the study. "This is a new finding, and it's impressive because the test is so simple."
Burkman will present results of the study today (June 2) at the meeting of the American Urology Association.
The acrosome is a enzyme-filled cap covering half the sperm head. Just before fertilization, enzymes from the acrosome, activated at the proper time, soften the egg's covering, or zona, allowing the sperm head with its genetic material to fertilize the egg. If the enzymes are released too soon, a process called premature acrosome reaction, the sperm is rendered useless.
Premature chromosomal decondensation refers to the untimely unraveling of the sperm's tightly packed genetic cargo. If this begins before the sperm has penetrated the egg, the sperm head swells and fertilization becomes impossible.
"In our study, when pregnancy occurred, we knew that the partner's sperm were capable of fertilizing the egg," Burkman said. "When pregnancy did not occur, the possibility existed that the sperm failed at one or more points in the fertilization process."
For this study, researchers analyzed semen samples from 250 consecutive patients who came to their andrology laboratory, housed in Children's Hospital of Buffalo. Samples were rejected if the male did not follow instructions carefully or if the samples were more than one hour old.
Each sperm slide was scored for percentage of sperm showing the premature acrosome reaction or evidence of chromosomal decondensation. These scores then were correlated with the couples' pregnancy results, grouped as natural pregnancies, intrauterine inseminations and in vitro fertilizations (IUI/IVF), or no pregnancies.
Results showed a very low incidence of chromosomal decondensation or acrosome reaction in the natural pregnancy group, while in the no-pregnancy group, the rates for both errors were significantly higher.
Based on these data, the researchers established fertility thresholds of 14 percent chromosomal decondensation and 7 percent premature acrosome reactions, then tested their criteria on subsequent new pregnancies. They found that of the 29 couples who later achieved a pregnancy, 82 percent fit the new semen criteria.
"Eighty percent of what we guessed would happen, happened," Burkman said. "This also means that only 20 percent of the problem semen cases could be linked to a pregnancy. So couples with either of these errors have greatly reduced pregnancy potential.
"Fifteen years ago, we knew so little about the human sperm that we couldn't come close to models for predicting pregnancy," she said. "We know much more now."
Also participating in the study were Kent Crickard, M.D., Frank Gonzalez, M.D., and Hemlata Bhakoo, Ph.D., all of UB and Children's Hospital, and MaryLou M. Bodziak of Children's Hospital.