Overweight effects the chances of becomming pregnant, both naturally and during artificial conception.

Whether one is overweight is determined by “body mass index” (BMI). BMI is defined as weight divided by height. A normal BMI is between 19 and 24. A BMI between 25 and 29 is defined as slightly overweight, 30-34 very overweight, and a BMI over 34 is defined as extremely overweight (obese).

Many overweight women have trouble getting pregnant. This is because their hormone system is disturbed by fatty tissue. This tissue converts hormones whose function is important in the female menstrual cycle. In case of obesity, it is not uncommon for the woman to experience irregular or no ovulation at all. There is also an increased risk of early miscarriage. In many cases, the pregnancy goes unnoticed because the menstruation comes late and is stronger than normal.

The chance of becoming pregnant through IVF (in vitro fertilisation) is also apparently lower for overweight women. The more overweight, the greater the problems. (See figure 4.)


Figure 4 shows the chance of becoming pregnant per IVF cycle based on the woman's body mass index (BMI). The statistics are taken from a survey of 3.586 IVF cycles at an English clinic.

The distribution of fatty tissue is also of importance. The more fatty tissue around the abdomen (ie. the more abdominal fat relative to hip fat), the greater the infertility problems.

Being overweight also increases the chances of complications during pregnancy and birth. Examples are high blood pressure, diabetes, and blood clots in the legs. The chances of giving birth to a living, healthy baby are less for overweight women.

Experience has shown that when overweight women lose 10% of their weight (or more in cases of obesity), 90% will resume regular menstruation – and ovulation.

Experience has shown that, of overweight women experiencing irregular menstruation, a weight loss of 10% (or more) results in regular menstruation - and ovulation– for 90% of them. Three fourths will become pregnant – one third of those without treatment. The risk of an early miscarriage is almost normal after the weight loss.

These findings have lead us to advise women with a BMI over 30 to lose 10% of their weight (or more in cases of greater overweight or obesity). This will help them achieve normal ovulation, acceptable chances of becoming pregnant without treatment, the best possible chances of becoming pregnant with treatment, and reduced risks for miscarriage.

We realise it is not easy to lose 10% of your weight.

Consult us if you need help in getting started losing weight.


Read more about other casuses of infertility