http://www.babyzone.com/askanexpert/answer.asp?qid=186
Can being overweight affect my chances of getting pregnant?
Before answer this question, we must take a look at how the body works. There are two sources of estrogen in the body: the ovary (directly) and the adrenal gland (indirectly). The ovary estrogen phasesup and downin what are part of the variations of a normal menstrual cycle. Additionally adrenal glands make something called androstenedione, which is related to cholesterol, and actually even testosterone and progesterone. So it's common that hormones often are converted back and forth. In the case of the adrenal androstenedione, fat cells convert it into estronean estrogen.
So, if you're significantly overweight, while your ovaries are trying to behave and cycle normally, the steady input of estrone from this other pathway will interfere. A steady supply of estrogen will blunt the peaks and valleys of the ovary's function, which ultimately interferes with ovulation. Also, all of this estrogen can even lead to precancerous changes in the womb (uterus)which are usually reversible.
Besides causing increased risk of heart disease, hypertension, and diabetes, obesity can also cause biochemistry to gang up on your chances for decent ovulation.
How can you tell whether you're the one who's going to be affected?
If you're having regular periods, then you're probably having regular ovulations. If the periods are sporadic, then probably so are your ovulations.
One extra note: thyroid problems can cause both irregular periods and obesity, so it isn't unreasonable to begin your infertility work-up with blood work to check for this.
http://www.bbc.co.uk/parenting/having_a ... ndex.shtml
Women
Look at your weight. Not being overweight helps conception and makes pregnancy more comfortable. A carefully monitored weight-loss diet can be safe during pregnancy and is sometimes advised for women who are seriously overweight, but always check with your doctor.
Being underweight can make you less fertile, while being overweight puts you at greater risk of complications such as high blood pressure and diabetes during pregnancy.
http://www.bbc.co.uk/devon/community_li ... tion.shtml