Mommy instinct

Mommy instinct is the concept that women who are pregnant or have given birth will somehow automatically know how to care for themselves and their children, better than any doctor or expert or family member who may have already experienced what the mother is dealing with. Sometimes, they can even extend this advice to other people or others' children. The concept is a combination of both the appeal to nature and appeal to no authority fallacies with sprinklings of bad appeals to common sense.

A dangerous idea
According to mommy-instinct doctrine, a woman experiencing a problem with her children or with her pregnancy should not seek advice from experts who know what they're talking about; she must "listen" to her own instincts and make what (she thinks) is the best decision. Problem: even after listening to instinct, she might still not have the answer, so she asks people who aren't experts, like the Pearls or nutritionists. At worst, she may elect to not seek help when the circumstances become the most dire, like during a child's epileptic seizure or in the case of an ectopic pregnancy.

Who buys the woo
Appealing to mommy instinct covers a broad number of areas of the wooniverse, including chemophobia, anti-vaccine hysteria, alternative medicine, nature woo, food woo, homeschooling, and many other types of anti-intellectualism. As such, it is promoted quite heavily on various social media sites such as Facebook and Pinterest by woomeisters who sell self help books and remedies to the gullible and those who don't want to be taken for sheeple.

Religious implications
Without calling it "instinct", some religions appeal to maternalism through their rhetoric or dogma. In Christianity, the maternal "instinct" is the calling all women must follow, painted by joy. Christianity as well as other Abrahamic religions also use childbirth as punishment for original sin and therefore an obligation, an idea that makes the anti-choice crowd happy. In this mindset, it's a woman's responsibility to give birth, thereby making them useful to the rest of society — a notion very admirable to the patriarchy.

Certain pagan religions, appealing to matriarchal concepts, state that a woman's power is in her uterus, since they're the ones who carry a pregnancy to term, suffer the ultimate pains of childbirth, and actually bring a new life into the world; therefore, they are stronger than the mens. The cults involved in the goddess movement also use childbirth to define a woman's worth, albeit from a somewhat ironic feminist perspective.

Ironically...
There are currently studies on birthing positions by the World Health Organization suggesting that the lithotomy (lying on the back), while making the medical personnel's job easier, is the most painful and damaging for the mother. The WHO suggests letting the mother choose the position she feels the most confortable with.