Obesity is a common phenomenon among women of reproductive age. In England and Western countries, a fifth of pregnancies are in women with obesity.
Many fertility problems are due to obesity and are common among overweight women: menstrual cycle irregular or rare, an increased risk of a lack of productivity, increased risk during fertility treatments, increased risk of miscarriage and reduced chances of successful fertility treatment.
Even when the pregnancy is successful, obesity leads to increased percentage of pregnancy complications: increase in blood pressure, the development of gestational diabetes, increased risk for birth defects, increased risk of having a high weight infants and increased likelihood for Caesarean section.
Moreover, infants to obese mothers are more likely to have neonatal development of obesity in childhood and obesity in adulthood.

General evaluation of accepted measures of overweight and obesity is the body mass index measurement, known as BMI (Body Mass Index).
BMI over 25 are defined as the excess weight, BMI over 30 are considered obese, and values ​​above 35 are considered morbidly obese, which is extremely conducive to the development of diseases such as diabetes, hypertension, hypercholesterolemia, heart disease, asphyxia apnea, back and joints pain and substantial disruption to the quality of life.

The rate of obesity among girls and young women has doubled in the last 25 years and most chances are that these girls will grow up to be obese women, this means their fertility damage is expected.

The link between obesity and fertility is mainly due to a decrease in the cycle of ovulation. One common syndromes associated with obesity and a decrease in fertility is Polycystic Ovarian Syndrome. which 4% -7% of all women have, but the prevalence increases to 61% among overweight women. Obese women with PCOS suffer more from lack of ovulation which results productivity damage.
The main mechanism which causes the lack of ovulation in women is due to the phenomenon of fat tissue resistance to insulin. This phenomenon is most common in women with abdominal obesity, also called apple-shaped obesity, and accompanied by hormonal changes that prevent normal ovulation cycles. Even overweight women with normal ovulation cycles have greater difficulty achieving pregnancy than women in normal weight.

Obese pregnant women, whether pregnancy was achieved naturally or after fertility treatments, have an increased rate of early abortions and recurrent miscarriages.
The reason for this is hormonal and due to insulin resistance, accompanied by high levels of insulin in the blood and obesity accompanied by high levels of leptin (fat hormone).
Obesity also causes an increased percentage of pregnancy complications, including imbalanced blood pressure, gestational diabetes, the development of blood clots and embolisms, infections, and mood swings.
Fetal complications also are at a higher rate, and include fetal distress, lack of fetal development, abnormal presentation of the fetus, and shoulder being stuck in the birth canal. It also indicates the need for labor by instruments and Cesarean section.

The rate of development of birth defects in fetuses in obese women rises by 7% for every extra BMI point, and that over the values ​​of 25.
Ability to test the accuracy of the ultrasound during pregnancy in obese women is affected, so this test is not accurate for 22-24 weeks in 10% of overweight and obese women, thus preventing early detection of fetal abnormalities.
Mortality rate are also dependent on the mother’s BMI and pregnant women exceeds four times in obese women. Preterm birth rates are higher in overweight women mainly due to pre eclampsia modes in the mother and premature newborn. Among women with extreme obesity, with a BMI over 40, one in 121 women gives birth to a stillborn.

The combination of risks to the mother and the fetus require weight loss prior to pregnancy, whether spontaneous or in the process of fertility treatments. To maintain a normal pregnancy and bring a healthy baby into the world, women should make every effort to reduce the weight before planning a pregnancy.
Many obese women go to fertility centers. They often need more cycles of hormonal stimulation to create follicles, but overall, the rate of pregnancy after three cycles in obese women are 41% compared to 50% in women with normal body weight.

Losing weight, even a 5% -10% of body weight, improves insulin sensitivity, increases the ovulatory cycles, improves hormonal balance in women with polycystic ovaries and increases the chances of a healthy pregnancy.