On the heels of previous research, another link between cigarette smoking and infertility has been uncovered. In the latest analysis, researchers at the University of California, Riverside examined the impact of smoke exposure on ovulation and egg function in a group of hamsters.1
Their study was published online in May at the website of the medical journal Biology of Reproduction.
"After fertilization, the pre-implantation embryo is transported to the uterus for implantation and further embryonic development," wrote lead researcher Prue Talbot, PhD, a professor of Cell Biology at the University of California, Riverside, and doctoral student Christine Gieseke. "Proper timing throughout all stages of [egg] pickup and transport is critical for successful fertilization and pregnancy."
Detrimental Impact of Cigarette Smoke
However, cigarette smoke has been shown in both animal studies and lab experiments to have a negative effect on reproductive function; specifically, in the ability of the egg to move from the ovary to the site of fertilization in the oviduct (fallopian tube).
"There are a number of epidemiological studies showing that women who smoke during pregnancy have fertility problems," Talbot told Priority Healthcare. "Unfortunately, the studies do not really clarify what is affected by smoke exposure. However, several adverse outcomes in humans (delayed time to conception, ectopic pregnancy, infertility) could be due to effects of smoke on the oviduct."
Digger Deeper for More Answers
To successfully move the egg through the oviduct in animals, the egg first must stick to the upper portion of the oviduct. This ensures that cilia, microscopic hair-like structures in the oviduct, can propel the egg along. In their study, Talbot and Gieseke wanted to determine whether exposing the egg and oviduct to cigarette smoke alters this process. They also wanted to know if the egg and its surrounding, cloud-like protective cells called cumulus cells (also known as the oocyte (egg) cumulus complex) were direct targets of cigarette smoke.
"We knew from prior studies that oviductal functions were inhibited in our model system by smoke solutions," Talbot told Priority Healthcare. "This was our first study to show that both the oviduct and cumulus complex are affected by smoke."
What the Study Uncovered
After exposing hamster oviducts and eggs to six types of cigarette smoke, the research team found that it did have a negative impact on how the eggs moved through the oviduct. Some eggs did not properly stick to the upper portion of the oviduct; other eggs stuck to the oviduct, but did not move at all; or some eggs properly adhered to the oviduct, but their movement was slowed.
Affecting the egg's transport through the tube could prevent subsequent conception. "The oocyte cumulus complex may be delayed, and so not arrive at the site of fertilization in time," Talbot explained. "Alternatively, the oocyte cumulus complex may not get picked up [by the oviduct] at all. If the latter occurs, there is an opportunity for ectopic implantation in the peritoneal cavity."
Other Negative Impacts
The two researchers also found that as the egg's adhesion to the upper portion of the oviduct increased, the likelihood that the egg was picked up by the oviduct to begin its trip to the site of fertilization was reduced. Medical experts point out that increased adhesion prevents the oviduct from picking up eggs after they are released from their follicles—a normal process of ovulation.2 In this study, between 40% to 60% fewer eggs were able to move through the hamsters' oviducts. "The mechanism that caused an increase in adhesion after exposure to smoke solutions is not known; however, it is known that the proper amount of adhesion is critical for oocyte cumulus complex pickup," they wrote.
When smoke exposure to the oviduct was removed, the investigators found that the eggs' adhesion to the oviduct was still well above normal.
Exposing most of the eggs directly to the various types of cigarette smoke also reduced the numbers of cumulus cells surrounding eggs that they need to properly ovulate, the researchers noted. Finally, they learned that cigarette smoke directly targets both the cumulus-coated eggs and the oviduct, though the oviduct experiences increased adverse effects.
Does the Same Hold True in Women?
While findings in animal studies can't always be reproduced in people, this study still has implications for women attempting pregnancy, wrote Mary Ann Handel, PhD, co-editor of the journal in which this study was published. The study, she wrote, "will … provide one more cautionary note about significant health effects of smoking."
There have been other studies on the effects of smoking in people relative to ovulation, embryo implantation, and pregnancy. "Present evidence supports an adverse effect of smoking on ovarian function, which is prolonged and dose-dependent," wrote researchers at the University of Florida who conducted a review of this topic in the medical literature.3
In one of the most recent studies to evaluate the effect of cigarette smoking on ovulation,4 doctors learned the exposing cigarette smoke to the cumulus cells surrounding human eggs during ovulation can lead to DNA damage in the cells.
Other experts contend cigarette smoking can boost the risk of miscarriage, and can negatively effect fetal development, such as slowing the baby's growth rate. In addition, nicotine can cause blood vessels in the uterus and placenta to narrow, and can negatively affect the blood pressure and heart rate of both the mother and developing fetus.5
"Smoking cigarettes during pregnancy … causes considerable health damage to the fetus and to the infant during the initial growth phase," wrote Knut-Olaf Haustein, MD, with the Institute for Nicotine Research and Smoking Cessation in Erfurt, Germany, in a 1999 review paper. "A smoking mother puts her child at considerable risk, not only of higher incidence of [miscarriage], premature ablatio placentae [premature separation of the placenta from the uterine wall prior to delivery], and reduced weight at birth, but also of deformities."6
1. Gieseke C, Talbot P. Cigarette smoke inhibits hamster oocyte pickup by increasing adhesion between the oocyte cumulus complex and oviductal cilia. Biol Reprod 2005 May 11;[Epub ahead of print].
2. Lam X, Gieseke C, Knoll M, Talbot P. Assay and importance of adhesive interaction between hamster (Mesocricetus auratus) oocyte cumulus complexes and the oviductal epithelium. Biol Reprod 2000 Mar;62(3):579-88.
3. Shiverick KT, Salafia C. Cigarette smoking and pregnancy I: ovarian, uterine, and placental effects. Placenta 1999 May;20(4):265-72.
4. Sinko I, Morocz M, Zadori J, Kokavszky K, Rasko I. Effect of cigarette smoking on DNA damage of human cumulus cells analyzed by comet assay. Reprod Toxicol 2005 May-Jun;20(1):65-71.
5. Economides D, Braithwaite J. Smoking, pregnancy and the fetus. JR Soc Health 1994 Aug;114(4):198-201.
6. Haustein KO. Cigarette smoking, nicotine and pregnancy. Int J Clin Pharmacol Ther 1999 Sep;37(9):417-27.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
