Most pregnancies we hear about are the extreme ones. Lengthy labors, morning sickness that lasts from conception to delivery or giving birth to a toddler-sized infant. But what is an "average" pregnancy?

Thankfully the average human pregnancy is far shorter than your average elephant pregnancy, clocking in at an average length of 280 days. This calculates out to about 40 weeks or 9.33 calendar months of 30 days, when calculated from the first day of the last menstrual period.

"In reality, this ends up being 266 days (38 weeks) from the time of conception (scientifically the most accurate, but when these numbers were first described, science did not know about the timing of conception)," says Dr. Eldridge Pearsall, an OB/GYN from Beverly Hills, Calif. Today's blood tests and ultrasound also help with accurate dating.

How much weight does the average woman gain during this time of housing and eating for two? According to Dr. Pearsall, the average weight gain during pregnancy is 2.2 to 4.4 pounds during the first trimester of pregnancy (up to 13 weeks) and 1 pound per week thereafter. This average ends up being approximately 28 pounds.

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