As above. Also, how would the answer to this title question explain babies that are born premature, or babies that are born so late that the labour has to be induced?
Thank you in advance! I have wondered this for a while!
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True, it’s not completely understood how or why women go into labor (which is crazy to me, given how many babies have been born! You’d think we’d know more!)
It is thought to have to do with a few different hormones working together – starting with a release of estrogen, which tells the uterus to be on the lookout for oxytocin, which is what starts the contractions.
pregnancy is a continuous process. mother, baby, and placenta are constantly exchanging messages in the form of hormones, nutrients, and immune cells.
its is thought that once a fetus’s lungs are developed, a signal is sent from the fetus to the mother that first initiates labor. that signal causes a “cascade” to begin. mom’s body releases estrogen, baby changes position and starts pressing on the cervix, the cervix starts changing, etc.
It’s really hard to say. Human reproduction is, to put it lightly, a giant hot mess. Much of it doesn’t make sense, and there’s always more factors at play than we realize.
There’s a lot of strict control over what research can be done on humans, particularly on fetuses and surrounding pregnancy. Much of what we have learned about early development is from IVF. I doubt we will ever really know.
There are some facts we do know, although they don’t really form a cohesive picture at this time.
Generally speaking in human pregnancy, the mother has almost no control. This is unique among mammalian pregnancy, most mother’s have at least some control over what the fetus can take, some can even terminate pregnancies that they feel won’t be successful. Humans can’t. It’s actually a reason humans menstruate, to ‘filter out’ weak embryos, and to preemptively build a lining that can prevent the placenta from breeching maternal blood vessels. So by that logic, it’s unlikely that a mother’s body has much say in when labor starts. Except for certain situations such as extreme dehydration, food poisoning, infections of the reproductive or urinary tract.
There’s some indication that as the placenta begins to wear out, it emits certain hormones that initiate labor. As others have stated, lung development seems to play a role. It’s believed that sex, orgasm, and nipple stimulation might trigger labor, and people at risk for preterm labor are recommended to avoid it. However, for people not at risk for preterm labor, it is generally considered a myth that those activities will trigger labor. Certain hormones produced in response to those activities are used in labor induction so maybe they could play a role. But so does natural light, blue light, and melatonin.
Typically, the beginning of labor is marked by loss of the mucus plug/”bloody show”, and/or rupture of the amniotic sac/”water breaking”. It’s possible to have both of these events without going into labor. It’s also possible for a mucus plug to regrow, and for a ruptured amniotic sac to heal. It’s possible for a cervix to dilate without a single contraction. In fact, I delivered my premature stillborn daughter without contractions, and the doctor only induced mild contractions to deliver the placenta.
But what about twins and triplets? Nearly all triplets are born early, and twins are frequently premature. It couldn’t be lung development or an old placenta. It’s thought that a contributing factor is excessive uterine distension. Literally there’s no more room to grow.
The last little while is like a practice run, and the body starts giving contractions more and more until there’s a cascade of hormones and it goes into full blown labor. Hospitals like to use Pitocin to speed things up, or get things going since the body makes oxytocin on its own to start things out, so that they can make sure the baby is delivered when they’re there.
The cervix being a certain dialation is key, because a baby will not leave unless the cervix (a donut with a larger hole the long into the pregnancy you get) is low enough and open enough to essentially “let go” of the baby. By that time, the baby has slipped into a head first position. The hormones are what softens the cervix and opens it up more, so by the time the baby is due, the hormones have done their job.
Certain developments have to occur in the baby as well. Some of the last things to develop are the lungs, which are crucial to the baby surviving outside of the womb.
In addition to other answers, there are several emergency eject buttons, as it were.
Most pregnant women won’t break their bag of water like you see in movies, but if it does happen due to either membrane sweeping (a way to induce labor,) trauma, or just pure happenstance, two things result: the fluid from inside the bag will come into contact with the mother and the bag will begin to deflate. Both of these will trigger the start of active labor in the mother. Her cervix will begin to dilate and her uterus will start ushering the baby into position if it isn’t already there.
This is really useful for something like preventing the baby from getting too big before birth because a will hopefully break the bag before getting too big to be born (obviously not always the case, but you can see the evolutionary benefit to having a semi-fragile bag.) Our embryonic development is limited by our brain growth, because the skull and the shoulders are the biggest diameters when we’re born. Newborn heads look straight up like [xenomorph skulls](https://bloody-disgusting.com/wp-content/uploads/2020/12/125689_Special-Effects-Mechanical-Alien-Creature-Head_7.jpg) because they have to be squeezed to fit through the birth canal.
I mean, I know that babies are not supposed to be born as early as they are. We should stay in for another 6 months to a year for development. We only come out because the baby’s head would be too damn big to fit through the vaginal canal and we would kill our mother trying to come out any later. If you look at most other mammals, they can move/crawl/stand/run right after they’re born. Humans are stupid
For all of us who have had to have a Pitosin drip to start mad labor for hours…No! Several things happen in combination: The lung will mature, a layer of fat develops on the child and helps with the normal weight loss after birth. Then a substance is sent from the child to the mother to start the process.
If you are a first time mother, the baby drops. Otherwise your cervix tilts forward and softens. This is when you feel the Braxton Hicks contractions as everything gets ready and you can have even a couple of cm. in dilation.
This is where it can go haywire. Some of us will do the drop and then a whole lot of nothing. Both my babies had to be induced. In the past, I would have died. I would have labored until my body gave up. As the baby was never removed surgically, both Mother and child died. In other cases of premature birth the lungs were not ready, but the birth started anyway.
So it should be the fetus sending a substance to the mother, but that does not always work correctly or at all.
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