Betsy Kilmartin and her husband tried to conceive a child for nine months with no success. They saw a doctor to find out what could be causing the problem and found out there wasn't any specific biological cause -- it was what's considered unexplained infertility.
"It's hard, you're on an emotional roller coaster," Kilmartin told CBS News.
She used the drug clomiphene, or Clomid, to stimulate egg production and increase her chances of pregnancy. A new study shows the drug, which has become one of the standard treatments for unexplained infertility, may be the best option for couples like the Kilmartins.
A study published in the New England Journal of Medicine looked at 900 couples who had trouble conceiving for at least a year despite normal reproductive function. The study tested the different medications that can increase chances for healthy pregnancy, looking for the greatest success of a live birth with the lowest chance of having multiples, one of the main risk factors for fertility drugs.
Researchers were particularly interested in comparing two common drugs that promote extra egg release to a newer treatment using an aromatase inhibitor called letrozole, which has shown promising pregnancy rates without increased birth defects in other studies. The study was conducted at 12 clinics across the U.S. by the National Institute of Child Health and Human Development. Women in the study were between 18 and 40 years old and had male partners with sperm counts healthy enough for artificial insemination.
Though in-vitro fertilization is also an option for women having difficulty conceiving, it is much less common because it is expensive and most insurance doesn't cover the process; using a drug to promote ovary stimulation is the most common therapy.
This study tested three ovary-stimulating drugs that increase the odds for pregnancy by releasing more eggs: clomiphene (Clomid) and letrazole pills, and an injectable hormone called gonadotropin. The two pills were blind tested against one another.
The results? "Clomid was much more efficient than letrozole, achieving a live birth rate of 23 percent," Dr. Tomer Singer of Lenox Hill Human Reproduction told CBS News. "The letrozole group only achieved 18 percent."
The rate of becoming pregnant with multiples -- twins or triplets -- differed among the medications significantly. The clomiphene group had the fewest multiple babies born per pregnancy, at 5.7 percent, compared to 14.3 percent in the letrozole group and 13.4 percent in the group receiving gonadotropins.
"Letrozole treatment offered no advantages over clomiphene treatment," study author Esther Eisenberg, M.D., of the Fertility and Infertility Branch of the NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, said in a statement. "Women in the letrozole treatment group had fewer live births, but four times as many multiple pregnancies as women in the clomiphene group."
Injected gonadotropin treatments resulted in the highest number of births, 32 percent, but many were multiples -- twins or even triplets. The group receiving gonadotropin had 24 twins and 10 triplets, whereas multiples born to women in the other drug groups were all twins.
Pregnancies with multiple fetuses can involve more complications, often leading to substantially lower birth weights and pre-term births.
"There's a higher rate of c-sections, more diabetes, more preeclampsia," Singer said.
Limitations of the study could have affected the results slightly, including the fact that because gonadotropin is an injectable instead of a pill it could not be blindly studied against the other drugs. Additionally, the study was designed to compare current treatments using either Clomid or gonadotropin as one result versus the newer letrazole instead of studying the three drugs separately. Lastly, no control group was included because researchers felt it would be unethical to deny real treatment to couples who were seeking fertility help after trying to conceive for between one and three years.
Nevertheless, study researchers believe that the evidence is strong that current standard therapy using clomiphene remains the most effect way to stimulate ovaries and increase healthy pregnancy odds for couples with unexplained infertility.
After her treatment with Clomid, Kilmartin became pregnant with her son Lucas, who is now almost two years old. "I love children, I've always wanted to be a mother," Kilmartin said. "It seemed like forever to get there."
Following another round of treatment, she is now expecting the couple's second child.
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