Weight loss can help in obesity-induced infertility.

Obesity can affect ovulation and the very chances of pregnancy. Can weight loss help? A weight loss program was assessed by the University of Adelaide, Australia, to determine whether it could help infertile overweight women to become pregnant without further medical intervention. Women in this study lost an average of 6.3 kg, with 12 of the 13 subjects resuming ovulation and 11 becoming pregnant.

In another study conducted by the University Hospital of Obstetrics and Gynecology, Heidelberg, Germany weight loss resulted in a significant reduction in blood glucose, insulin, and sex hormones concentrations. The pregnancy rate was 29% in this group and of them, 80% showed an improvement of their menstrual  function. Thus, weight reduction is the appropriate treatment for women with obesity-related endocrine derangement, menstrual irregularity and infertility.

While obesity is associated with poor pregnancy outcome and miscarriage and is a risk factor for both maternal and fetal complications, and the optimal weight gain or loss during pregnancy remain controversial. Dietary advice should be offered on an individual basis according to the pre-pregnancy BMI, concluded researchers at St Thomas' Hospital, London, UK.

On the other hand, pregnancies following even such a drastic measures as weight loss surgery or Fluoxetine, were possible and even  less complicated than pregnancy in obese women.

It's OK to lose weight before and after, but not during pregnancy!

Luckily, moms-to-be are wise enough to avoid losing weight during pregnancy

Weight loss attempts among women who report being pregnant are uncommon. Only 3.7% out of 1794, interviewed in 47 states reported that they are trying to lose weight while being pregnant. These attempts were more likely to occur in the first trimester and among women who smoke and drink, have diabetes or are very overweight.

Weight loss during the first month of pregnancy can cause neural tube defect.

France Central East Registry of Congenital Malformations presented data on pregnant women who lost 2 to 14 kg during the first month after conception and whose fetuses developed neural tube defects. Researchers suggest a hypothesis that the ketone body concentration increased due to weightloss in early pregnancy is a risk factor for neural tube defects.

However, taken the entire pregnancy course, your child seems to be  protected more than you probably thought.

734 women and their baby daughters born at the University of Amsterdam Hospital between August 1944 and April 1946, were examined before, during, or after a severe famine of the Hunger Winter. The results suggest that acute maternal under-nutrition affects fetal growth only below a certain threshold of severe irreversible malnutrition after which even after these mothers were sufficiently fed, their daughters birth size did not respond by adequate growth.  

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Hum Reprod, 10(10):2705-12 1995
Minerva Ginecol, 48(9):333-44 1996
Br Med Bull, 53(2):341-58 1997
J Clin Nutr, 66(5):1116-24 1997