"She has an increased risk of uterine atony, or failure, of the uterus to contract after delivery, which can cause life-threatening blood loss and may require hysterectomy," said Wenstrom, who added that women who have multiple pregnancies are at risk for a condition called placenta previa. In such cases, she said, "the placenta implants over the cervix -- also associated with life threatening bleeding."
Although it seems only time is limiting the number of children that families like the Duggars can have, doctors say each pregnancy actually scars the walls of the womb, leaving limited real estate for a new pregnancy.
"Every time you have a pregnancy, the placenta implants in the uterus and that implantation site cannot be used again because it's scarred," said Dr. Diane Harper of the University of Missouri in Kansas City.
The more children you have, the more likely the placenta will implant in an inopportune place such as over the cervix (placenta previa). "You run the risk of developing problems with the placenta attachment," Harper said.
Going through 19 labors also stretches the mother's pelvic muscles and ligaments, sometimes to the point of causing uncomfortable or embarrassing problems.
Moms who've had multiple pregnancies usually have short labors and they're usually able to push the baby out with relatively little effort, according to Harper. But the elasticity of their pelvic floor can cause other problems.
If a baby starts to come prematurely, doctors have greater difficulty keeping the woman from delivering, Harper said. If the muscles around the uterus are sufficiently weakened, the result may be a condition called uterine prolapse, in which the uterus drops partway into the vagina.
The weakened muscles can also leave a woman incontinent, Harper said.
"The abdominal wall will lose all tone, causing intestinal hernias as well as putting intestines at risk for volvulus [a bowel twisted in a loop]," said Harper.
Other doctors say it is not so much the number of pregnancies that put the average women at risk as her age.
"From an obstetric point of view, the number of children is less important than the maternal age at time of birth, history of obstetric complications, and general maternal health," said Dr. Lauren Streicher, assistant professor of obstetrics and gynecology at the Feinberg School of Medicine in Chicago.
For example, older parents are more likely to have children with genetic abnormalities such as Down syndrome. The Mayo Clinic also points out that older woman are also more likely to develop preeclampsia -- the condition that sent Michelle Duggar in for an emergency C-section Thursday.
Despite all the risks, Duggar has shown the human body is capable of reproducing successfully for decades.