When does placenta take over

[S0987]

So here's what's confusing me:

www.newscientist.com/article/dn27460-womb-milk-nourishes-human-embryo-during-first-weeks-of-pregnancy/amp/

This article basically says the placenta doesn't take over until 11 weeks and until then baby is nourished by womb milk. I'm confused because if that's the case why are we told not to consume or do certain things during early pregnancy for want of protecting baby? I'm not saying let's all go drink and smoke it for the first trimester (I literally am the person who made myself vomit because I accidentally consumed a cherry seed and read that it's poisonous) I am just confused by this if you know what I mean?

Thanks

Forgot to say so basically if placenta doesn't take over and mother doesn't start sharing her blood supply with baby until 11 weeks then surely whatever mother consumes or does in that early stage can't affect the baby?!

Something must start happening around 5/6 weeks because that's when boobs start to really hurt and morning sickness is a thing.

I've always been told it was 10/11 week stage it took over and that's why people start to feel better by then.
Can't answer why really as to why told not to do certain things etc before this.
Someone will come along who knows.

After 9 weeks is when the placenta starts to form

I don't know the official answer but can only assume it's because there may be discrepancies between how far gone someone is, until the dating scan at 12 weeks? Perhaps it's safer and less confusing to say from the start that things should be avoided, plus it sets you in good practice to be aware of things I suppose, before it really does have an impact?!

@Lockdownbear I think that something is raise is HCG levels (or so I've read) but still doesn't answer why we are told to be so careful in the first trimester when actually apparently the placenta doesn't take over until later on!

@cherrytreecottage yes maybe that's why it's just easier to say avoid x y z at all times instead of giving a cut off date. To me it makes sense if this was true why some people who don't realise they are pregnant until much later like second trimester have perfectly healthy babies even though they've continued eating and drinking the way they normally would....

My understanding is that something like heavy drinking or drug use is all or nothing in early pregnancy: if you're unlucky then it can prevent the embryo from implanting properly and cause miscarriage; if you're lucky then it probably won't have any effect at all.

I would also say that smoking and alcohol isn’t also just about crossing the placenta and getting to the baby, it’s about the health of the mother. For example, smoking causes poorer lung health meaning less oxygen absorption meaning a less healthy “host” for the embryo to be in. Also the toxins from drug and alcohol use don’t just disappear when you stop, some have much longer effects so maintains health from the start of the pregnancy (or even before) is encouraged.

It’s the same with food restrictions, cutting down on raw meat/fish isn’t because it could cross the placenta, it’s about reducing the risk of listeria etc. which would cause symptoms that make the body an undesirable host, such as having a fever.

I think the article does explain it, although in quite a bit of an unclear way. My interpretation is that given our bodies are creating the 'womb milk', logically what we eat and drink would surely impact the quality of it - i.e. avoiding alcohol means it is more likely to be 'good' and not have any toxins from alcohol in it

It says that "next, Aplin and his colleagues hope to investigate how a mother’s diet and other factors, such as smoking, affect the build-up of glycogen in the womb lining." The article is pretty old now (2015) so I think that they must have done the further research into that by now so hopefully there is more out there.

Most foods that you can't eat in pregnancy are more because of risk of food poisoning rather than because they contain anything bad that shouldn't pass through the embryo/ fetus. The infection caused by Listeria can cause miscarriage so that's why we're recommended to avoid soft cheeses.

It's interesting this article has got everyone thinking hasn't it lol

I found something more recent from July 2021 about the yolk sac and how it nourished the baby until the placenta takes over:

www.whattoexpect.com/pregnancy/fetal-health/yolk-sac-ultrasound

Maybe it is the case that the nutrients that go in to making the yolk sac are based on what a mother consumers but I find it quite hard to think that like because you ate a raw prawn or drank some wine that would form the basis of the yolk sac or womb milk feeding the baby (although it could be perfectly true).

We need some doctors on here!!

It's true that drinking alcohol in the first 9-10 weeks of pregnancy will not get passed to the baby via the placenta.

However, it can potentially affect hormones and very marginally increase the risk of miscarriage. As can caffeine. Alcohol and caffeine can also reduce the chance of conception in the first place - so reduce your chance of getting pregnant at all (although this is more of a factor if you're older, and obviously lots of people get absolutely trollied and still get pregnant).

As PPs have said - the "raw prawn" advice isn't so much about the toxins you pass to the baby - it's about avoiding getting food poisoning (e.g. listeria) which is much more serious if you are pregnant and again can lead to miscarriage.

"womb milk" is still a product of the mother's body - it is a secretion from the lining of the uterus that is taken up by the developing placenta - do things that the mother consumes/does can affect the womb milk and hence the baby.

Think how big a baby is by twelve weeks. That mass has to come from somewhere and mum is the only option!

I dislike the term "placenta takes over" as it's a bit unclear as to what it means - take over what? The placenta does take over from the corpus luteum in producing progesterone at around 10 weeks (roughly), but the placenta begins to form much sooner than this and gradually starts to supply the embryo with nutrients, taking over from the yolk sac, well before the fully integrated blood supply settles into place.

It's a fascinating area and quite hard to find useful information that isn't dumbed down about it. I'd love more links!

Right guys I found the following article which if i try really hard to interpret to me means that the yolk and maternal proteins support the baby until placenta kicks:

In all mammalian species nutrition of the conceptus is initially histiotrophic, with the trophectoderm phagocytosing first oviductal and then uterine secretions. Following implantation and establishment of the chorioallantoic placenta there is a transition to haemotrophic nutrition, with exchange between the maternal and fetal circulations. It has long been assumed that the transition occurs soon after implantation in the human, due to the invasive nature of this process. However, the recent realization that the maternal circulation to the placenta is not fully established until the end of the first trimester casts doubt on the validity of this assumption. There is new evidence that the uterine glands discharge secretions into the intervillous space until at least 8 weeks of pregnancy, and that these are taken up by the syncytiotrophoblast. Also, during early pregnancy selected maternal proteins accumulate within the fluid of the coelomic cavity, from which they may be transported to the fetus by the secondary yolk sac. Histiotrophic nutrition may be advantageous to the fetus during the first trimester as it provides nutrients under a low oxygen concentration, so reducing the risk of free radical mediated damage during the sensitive period of organogenesis. Once this is complete, and fetal oxygen requirements rise, there is a transition to haemotrophic nutrition at the start of the second trimester, when the maternal placental circulation is fully established.

I am also very confused by this, especially as Expecting Better concludes that drinking is more risky in the first 12 weeks. It does make sense to me that current diet would impact current womb secretions, but I still need someone to explain to me how moderate drinking could impact the development of the foetus before the placenta is fully at play.

What particularly irks me is that a lot of advice against drinking simultaneously warns against drinking during conception - and scores of women are walking proof that that isn’t a problem.

It is a very weird thing and research is basically just a giant don't even look at booze even if TTC. I just read an article which said not to even drink non alcoholc beer as there might be traces (bit extreme in my opinion)!

I'd guess that in the week 5-8 stage the neural tubes etc are developing so you wouldn't want to drink, and then after that the placenta takes over so then that makes sense not to drink. I didn't know i was pregnant with my DD and drank a fair bit up to week 5 when I found out, and my doctor could not have been less concerned about that. Later on in pregnancy I had maybe a glass of wine once every 2-3 weeks in the third trimester and I would say it was a contributing factor to dehydration which ultimately put me in early labour, so that is the other side effect it can have which maybe is less considered. As a side note our child is completely fine, so there was no effect except potentially that deydration + too much exercise was too much to keep my DD in to full term.

@S0987

I agree with your interpretation! I think it is saying that the embryo is "histiotrophic" ("womb-eating") at first, during which various foetal tissues including the yolk sac and developing placenta, take up nutrients secreted by the uterus walls. Therefore things the mother consumes could theoretically end up in these secretions and thus get into the baby.

@Moancup I'm not at all an expert in this, but I would guess that the reason drinking is said to be WORSE during early pregnancy is because this is when development is happening most intensively, meaning there's more for alcohol to disrupt iyswim. Alcohol can get into the baby via uterine secretions even early on and cause problems, even if the amount that gets across is smaller than it would be later on in pregnancy when placental blood flow is fully established.

This is another problem with the "placenta doesn't take over till 12 weeks" statement - it gives people the feeling that they have a bit more wiggle room in the first trimester and things they do won't affect the baby, when there are some very clear examples (e.g. thalidomide) of this not being the case.

I think you need to separate two things here.
The placenta ‘takes over’ progesterone production to maintain pregnancy, that is correct. The placenta becomes the only source of blood and nutrients to the baby and the placenta is an excellent ‘barrier’ for preventing lots of things getting to baby, also correct.
But, before the placenta has formed and is doing all that, how’s the foetus getting it’s bloody supply? That’s right, directly through your blood. With no extra placental filter.
So whatever is in your blood, gets to baby - teratogens/toxins like alcohol included. And in the first trimester is when most of the key organs are forming and alcohol can directly affect all of that.
Hence all the advice to avoid completely if possible.

I personally think we need to find out whether the mothers intake is transferred into this uterine lining then yolk sac and therefore goes into baby. I don't think that's the case for some reason I'm not sure why - I feel like it must just be fats and proteins stored in the uterine lining or endometrium overtime that then are secreted (although I might be completely wrong but I'm going to research!)

I just find it hard to believe alcohol would somehow make its way into the uterine lining through your blood supply and then into the baby. With the placenta it makes sense because it's soul purpose is to transfer blood supply

I just find it hard to believe alcohol would somehow make its way into the uterine lining through your blood supply and then into the baby. With the placenta it makes sense because it's soul purpose is to transfer blood supply

Why? Alcohol is good at permeating tissues and exerting effects away from the blood supply (it can certainly cross the blood-brain barrier, for example). Plenty of other molecules cross into the embryo too, like the aforementioned thalidomide. In any case, there are studies that show foetal alcohol syndrome can occur even when the alcohol consumption was only in the first trimester, e.g., quoting an abstract:

"This study examined 17 children (nine males, eight females; mean age 13 years) with prenatal alcohol exposure of various durations. The aim of the study was to detect specific brain morphological alterations by means of MRI and to see if findings correlated with particular cognitive deficits. Of the 17 children, five had been exposed to heavy maternal consumption of alcohol (over 10 drinks/week) during the first trimester only; four had been exposed during the first and second trimester; and eight had been exposed throughout pregnancy. Five children had alcohol related neurobehavioural disorder, seven were diagnosed as having foetal alcohol effects and five were diagnosed as having foetal alcohol syndrome. Hypoplasia of the vermis was observed in 10 children and malformed posterior vermis in one additional child. Five children had hypoplastic cerebellar hemispheres. Hypoplasia of the corpus callosum was observed in two children. Small hippocampi were observed in three children and wide cortical sulci in six. No specific structural anomaly correlated with a particular neuropsychological deficit. In this study, deviations in the development of the vermis was the most sensitive morphological indicator of the effects of prenatal alcohol exposure. It was seen in every diagnostic group including children who had been exposed during only the first trimester of pregnancy."

Link: pubmed.ncbi.nlm.nih.gov/11848116/

I typed "effect alcohol embryo first trimester" into scholar to find it. Unfortunately I don't have time to do much more research right now, but I did find two papers that promise to be about how alcohol effects extremely early pregnancy (pre-implantation):

cdnsciencepub.com/doi/abs/10.1139/bcb-2017-0133
cdnsciencepub.com/doi/abs/10.1139/bcb-2017-0141

@CoalCraft yes I guess this all shows that it does affect early pregnancy and therefore the uterine lining must be taking up whatever the mother consumes. Otherwise this research wouldn't make sense???

@S0987

I personally think we need to find out whether the mothers intake is transferred into this uterine lining then yolk sac and therefore goes into baby. I don't think that's the case for some reason I'm not sure why - I feel like it must just be fats and proteins stored in the uterine lining or endometrium overtime that then are secreted (although I might be completely wrong but I'm going to research!)

I just find it hard to believe alcohol would somehow make its way into the uterine lining through your blood supply and then into the baby. With the placenta it makes sense because it's soul purpose is to transfer blood supply

No, it LITERALLY travels in the bloodstream. From the mother’s blood into the baby.

Also, the endometrium is FULL of blood and blood vessels. It’s not about any stored fats or proteins.

pubmed.ncbi.nlm.nih.gov/22595965/

Quick search result to show that foetal blood alcohol levels EQUAL maternal blood alcohol levels within 2hrs.