Is there a right amount of weight for women to gain while pregnant? According to the experts, there most definitely is, but that number tends to become more important when you're in the public eye.

The very pregnant Jessica Simpson has been held up as an example of excessive maternal weight gain by various media outlets, with The View's Joy Behar calling her "fat," and an ob-gyn telling Slate, "she's an absolute porker."

But Simpson has apparently only gained 40 pounds, just a bit over Health Canada's recommendation of 25 to 35 pounds for those of normal weight. The agency has a Pregnancy Weight Gain Calculator available to help determine healthy weight gain for both the baby and the mother.

Of more concern is Simpson's own admission that she's taken "a break from working out," according to Hello! Magazine. Exercise during pregnancy can help prevent maternal obesity, which in turn has been linked to many potential issues, including high blood pressure, miscarriage and autism in the child.

Michelle F. Mottola, of the University of Western Ontario's Exercise and Pregnancy Laboratory, has broken down the specifics of exercising while pregnant, and has determined that not only should mothers keep working out while carrying their child, but it can be a good idea to start a program at that time too.

In a paper entitled "Exercise In Pregnancy and the Postpartum Period," co-authored by Mottola, the recommendation includes15 minutes of continuous exercise three times a week, increasing gradually to 30-minute sessions four times a week for those who hadn't exercised previously. Suggestions for activities include brisk walking, stationary cycling, cross-country skiing, swimming, or aquafit are aerobic exercises -- exercises that aren't particularly bouncy or traumatic to the joints and ligaments. And for those who haven't exercised before, wait until the second trimester to get going.

As for Simpson, her plans reportedly include joining Weight Watchers as a spokesperson -- a program that worked for new mom Jenny McCarthy in the past.

SEE: Many celebrities have opened up about their weight gain during pregnancy -- and their own reactions were varied:

• Jessica Alba
• Jennifer Garner
• Leah Remini
• Kate Hudson
• Jenny McCarthy
• Gabrielle Reece
• Jennifer Lopez
• Gisele Bundchen

CORRECTION: This article incorrectly stated that Mariah Carey had also done Weight Watchers after giving birth. In fact, Carey is a spokesperson for Jenny Craig. The text has been changed.