Being underweight or overweight may disrupt the normal process of consistent ovulation and is considered as a significant risk factor affecting the success rates of assisted reproductive procedures. Now, a study published in the journal, Fertility and Sterility, reports that female obesity reduces in vitro fertilization (IVF) outcome without affecting the embryo quality, indicating its effect in altering the uterine environment.
The study, headed by José Bellver from the Instituto Valenciano de Infertilidad, Spain, conducted a retrospective study to evaluate embryo quality and reproductive outcomes including implantation, pregnancy, miscarriage, and live birth rates, by analyzing 6,500 IVF-ICSI cycles. Based on body mass index (BMI), the women were categorized into 4 groups: lean (<20 kg/m2; n=1,070), normal (20–24.9 kg/m2; n=3,930), overweight (25–29.9 kg/m2; n=1,081), and obese (≥30 kg/m2; n=419).
The results did not show any difference in insemination procedure, fertilization rate, day of embryo transfer, average number of transferred and cryopreserved embryos, percentage of blastocyst transfers, or embryo quality on day 2 and 3 between the four groups. However, the researchers noted significantly reduced implantation, pregnancy, and live birth rates in obese subjects. With each unit advance in BMI, pregnancy and live birth rates showed a progressive reduction with a significant odds ratio of 0.984 and 0.981, respectively. Also, the collective rate of pregnancy after the completion of four IVF cycles showed a substantial reduction with increase in BMI.
Earlier, Martinuzzi, et al. (Journal of Assisted Reproduction and Genetics, 2008) reported that elevated BMI does not adversely affect the clinical pregnancy rates of young women with normal ovarian reserve opting for infertility treatment. During the retrospective study, the researchers analyzed 417 first, fresh IVF attempts conducted between October 2004 and December 2006. All study participants below 35 years of age, showed normal cycle day 3 follicle stimulating hormone and estradiol concentrations. Based on the BMI, the subjects were categorized into four groups with BMIs of <18.5 kg/m2, 18.5–24.9 kg/m2, 25–29.9 kg/m2, and ≥30 kg/m2. The researchers observed a greater difficulty in visualizing the air bubble location during embryo transfer and reduced implantation rates at elevated body mass indices. Cancellation rates, peak estradiol concentrations, and mean number of oocytes retrieved were comparable among the groups, in addition to similar clinical and ongoing pregnancy rates.
Contrary to these findings, Sneed and co-workers (Human Reproduction, 2008) reported that increased BMI has a profound negative influence on infertility in younger patients opting for IVF, and the effect gradually reduces with increase in the patient’s age. Beyond 36 years of age, the impact will be minimal.
The current study, validating the negative effect of BMI on IVF outcome, may help physicians to educate patients regarding the management of this risk factor to improve the chances of conception and live birth rates. However, further researches and clinical trial studies are mandatory to explore the age-related effect of BMI on IVF outcomes.
References
1. Bellver J, Ayllón Y, Ferrando M, et al. Female obesity impairs in vitro fertilization outcome without affecting embryo quality. Fertil Steril. 2009 Jan 24. [Epub ahead of print].
2. Martinuzzi K, Ryan S, Luna M, Copperman AB. Elevated body mass index (BMI) does not adversely affect in vitro fertilization outcome in young women. J Assist Reprod Genet. 2008 May;25(5):169-75.
3. Sneed ML, Uhler ML, Grotjan HE, Rapisarda JJ, Lederer KJ, Beltsos AN. Body mass index: impact on IVF success appears age-related. Hum Reprod. 2008 Aug;23(8):1835-9.
