A list of myths associated with pregnancy is nearly as long as the actual gestation of a baby. That is, assuming we change the metric by which we measure "length" from inches or feet... to "months."
Anyway, some of the most popular pregnancy myths are: cocoa butter prevents stretch marks -- it does not; don't dye your hair -- you can; don't fly -- feel free to; don't date Gary Busey -- actually, you probably shouldn't date Gary Busey while you're pregnant, and don't pet your cat. This is not a euphemism. You can pet your feline friend all you want during pregnancy. Although, it's a good idea to stay away from the litter box for fear of toxoplasmosis (a parasitic disease found in the cat's poop.)
Now, the one thing each of these myths has in common is that they relate to the pregnant woman. However, women aren't the only ones grappling with junk science, hyperbole and misinformation during pregnancy. Men are, too. The difference being that the list of myths men fear is precisely one item long.
The one and only thing men fear during pregnancy is that during sex, they will poke the baby in the head with their penis. Amazing, right? At a time when a couple's life is uniquely and specifically focused on the needs of the woman, men find a way to make it about how big their penis is.
So, what's the truth? Is it possible for a man to poke the baby in the head with the tip of his penis while he's having sex with his partner or wife? Before we tell you if the answer is "this" or "that" -- "yes" or "no," first, a brief anatomy lesson.
The growing baby is floating inside a sac of amniotic fluid which is floating inside the amniotic sac inside the uterus. The uterus is protected by the cervix, a rigid barrier to the vagina which slowly opens over the course of the pregnancy. The birth canal is 3 to 7 inches in length, depending on the woman's state of arousal.
The ultra sound picture above is of an actual penis inside a woman who is six months pregnant. The white colored area above the penis is the cervix. Beyond that is the uterus, amniotic sac and baby. As you can see, the direction of the penis is down. During sex, the penis fits in a space underneath the cervix and uterus.
So, what's the answer? Can you poke the baby in the head during sex with the tip of the penis? No. It's not possible, because the baby is protected behind the rigid cervix, uterus, and amniotic fluid.
It is possible to "jostle" the baby.
Yup. It's possible for a man, regardless of his penis' length, to gently jostle the baby.
However... It's no more of a jostle than the baby would experience if the pregnant woman were to run up a set of stairs or to exercise. As you can see from the photo, it's quite possible for the shaft of the penis to "brush up against" the cervix, which could, in turn, "jostle" the contents of the amniotic sac... and thus, "jostle" the growing baby.
Source: Huffington Post