Is Obesity Causing Infertility?

Obesity and IVF trouble are possibly linked

(RxWiki News) Did you know that one out of every three American women of childbearing age is battling obesity? And the consequences of this condition can affect fertility.

A new study investigating the correlation between severe obesity and the failure of in vitro fertilization, or IVF, was conducted at Brigham and Women's Hospital (BWH) in Boston, Massachusetts.

"Talk to your doctor about safe ways to fight obesity."

IVF is a manual process of fertilization that involves combining an egg and sperm in a laboratory dish.

If the IVF procedure is successful – this happens when the egg is successfully fertilized – the fertilized egg goes through a procedure called embryo transfer in which the embryo is physically placed in the uterus.

The study was led by Catherine Racowsky, PhD, Obstetrics, Gynecology and Reproductive Biology and director of the Assisted Reproductive Technologies Laboratory at BWH and performed by Ronit Machtinger, MD, of BWH, in collaboration with Catherine Combelles, PhD of Biology, of Middlebury College.

The investigation was conducted because of data indicating that obese women often have poor reproductive outcomes. The reasons for these poor outcomes have not been clearly identified.

Racowsky and team looked at 276 mature human eggs that failed to fertilize in the IVF process; 105 were from severely obese women – defined as having a body mass index (BMI) between 35.0 and 50.1 kg/m2 – and 171 eggs were from women with a normal body mass index (BMI) – defined as between 18.5 and 24.9 kg/m2.

Body mass index, or BMI, is a figure that is calculated using a person's weight and height. BMI is used to look for weight categories that may cause health problems.

Dr. Racowsky explained that this is the first study to reveal how BMI may negatively affect egg quality in women. He argues that, "These observations provide novel insight into a possible cause for the reduced likelihood of success with IVF in severely obese women."

An egg has the best chance of successful fertilization and supporting embryo development when it has one organized set of chromosomes attached to one spindle; this is considered a "mature" egg.

However, the study found that severely obese women typically have a greater chance of having eggs containing multiple spindles with disorganized chromosomes. Dr. Racowsky and team found these two specific facts during observation:

• Nearly 60 percent of the eggs from the severely obese group had two spindles, while only 35 percent of the eggs from the normal BMI group had two spindles.

• Among the eggs with one spindle, nearly 30 percent of the eggs from the severely obese group had disorganized chromosomes, while only 9 percent of the eggs from the normal BMI group had disorganized chromosomes.

The spindle attaches to the chromosomes in order to pull a set of chromosomes apart during the fertilization so each set of chromosomes from the sperm and the egg to combine the chromosomes. 

Racowsky made sure to point out that this study only involved eggs that had been stimulated through IVF and had then failed to fertilize; she did not hold this data to be true for all failed egg fertilizations in general.

She stated that more research needs to be conducted to fully understand what is causing the spindle abnormalities and disorganized chromosomes.

This study was published on September 11 online in the journal Human Reproduction.

Review Date: 
September 23, 2012