For women undergoing assisted reproductive treatment, having a previous unilateral oophorectomy was associated with lower odds of pregnancy and live birth, according to a meta-analysis published in Fertility and Sterility.
“I found it strange that in the literature, only a few [studies] have suggested a negative effect of removing a whole ovary in women’s fertility, and I thought it would be worth it to investigate this issue,” Kenny A. Rodriguez-Wallberg, MD, PhD, adjunct professor in the department of oncology-pathology at Karolinska Institute in Stockholm, Sweden, told Healio. “There is convincing data from large studies including a large number of women indicating that women with one ovary come into menopause 1 year earlier than women with two ovaries. If that effect on menopause could be identified in such large studies, I thought that the effect on fertility also could be found if we could analyze a very large sample of women.”
Identifying studies for analysis
Rodriguez-Wallberg, who is also a senior consultant of reproductive medicine at Karolinska University Hospital and head of the laboratory of translational fertility preservation at Karolinska Institute, and colleagues identified 18 observational studies published before June 1, 2021, that included women who underwent in vitro fertilization or intracytoplasmic sperm injection (ICSI) and who either had a history of unilateral oophorectomy (UO) or intact ovaries. There were 1,057 IVF/ICSI cycles in women with previous UO and 45,813 IVF/ICSI cycles in women with intact ovaries.
According to the researchers, the studies in their analysis were moderate to high quality based on the Newcastle-Ottawa Quality Assessment Scale, although some small studies had low statistical power. The studies also showed a high level of heterogeneity due to differences in methodology, they said.
Reduced pregnancy, live birth rate
Five studies published between 1997 and 2017 included information on live birth rates. Analysis of these studies showed the live birth rate was significantly lower in women with UO history compared with controls, with low heterogeneity (OR = 0.72; 95% CI, 0.57-0.91).
Among all studies included, 15 reported the rate of pregnancy per IVF/ICSI cycle as an outcome. Like the live birth rate, the pregnancy rate per treatment cycle had low heterogeneity between studies and was significantly lower in women with UO(OR = 0.7; 95% CI, 0.57-0.86).
The researchers separately analyzed the correlation between pregnancy rate and the number of oocytes received and embryos transferred based on when studies were published.
Before 1992, there was no significant correlation between pregnancy rate and number of retrieved oocytes. Controlling for oocyte retrieval, there was “a significant negative correlation between the number of transferred embryos and pregnancy rate (estimate, –0.43; P = .0107) and a significantly lower pregnancy rate in the UO group than in the control group (estimate, –0.77; P < .0001),” the researchers wrote.
After 1992, there was only a significant correlation between pregnancy rates and the number of oocytes when patient group was not counted as a covariate (estimate, 0.11; P < .0001).
“Additional analyses including age and number of transferred embryos showed no effect of age, but a negative trend with increasing number of transferred embryos,” they wrote (estimate, –0.36; P < .0001).
Gonadotropin use was assessed in 15 studies, analyses of which revealed that women with UO had significantly higher dosages of gonadotropins and significantly lower numbers of retrieved oocytes compared with controls. However, heterogeneity remained high despite employing a random effects model.
“It seems to be so obvious that women who lack one ovary should have lower fertility, but the study of fertility is complex, and our finding is novel, as it has not been demonstrated before,” Rodriguez-Wallberg said.
However, the researchers warned that because the studies were largely heterogenous, the findings should be interpreted with caution.
In practice, the results from the meta-analysis can inform the decision to perform UO in women who are more likely to need assisted reproductive technology treatment.
“Given that the biological reserve of eggs is finite, we should in some cases also offer women with low reserve of eggs to freeze their eggs ahead of a surgery that may affect their future fertility,” Rodriguez-Wallberg said.
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