Many pregnancy complications cluster around issues with the placenta, the first fetal organ to form in a pregnancy. Here at the end of 2025, this organ still holds a significant amount of mystery. It's a wily organ that comes in many different forms across the animal kingdom. Even looking at how other mammals have handled the job of nutrient delivery, gas exchange, and waste removal during pregnancy, suggests a diversity of ways these jobs can be managed, emphasizing different benefits and costs in a pregnancy.

Looking at how these benefits and costs show up in a cellular conversation between the placenta and the cells of the maternal uterine lining across a select group of mammals, including humans is a new way to understand this organ.

How the placenta develops and the ways in which that development affect both the mother and the pregnancy have been a mystery since pregnancy became a subject of study. Much of medicine focuses on the symptoms that come from pregnancy complications and tries to find a way to fix if not the problem, then the symptom.

Today's guest who looks at pregnancy with an evolutionary biology perspective that asks not only how the system works, but why the system works the way it does i.e. why are human placentas so invasive when other mammals have placentas that are not as invasive. Answers to the why questions can shape the ways in which we manage the how.

To find the paper we're discussion today, Cell ype and cell signalling innovations underlying mammalian pregnancy, see: https://www.nature.com/articles/s41559-025-02748-x

We all know the placenta as this life giving organ, the first to develop in pregnancy; a critical connection between mother and fetus that sends food and oxygen to the baby and eliminates the fetal waste products. Only recently did I trip over the fact that it takes a minute to make this incredible organ.

How long does it take and while its under construction?

How exactly is the embryo and then fetus being fed ?

In fact, it takes about eight or nine weeks for your body to build a placenta and then a few weeks to get the hookup to the mother's body, which takes us to roughly the end of the first trimester, 10 to 12 weeks or so.

So if that's the case, you might be wondering: how is that embryo getting food for the first 12 weeks? Doesn't it need food to grow and oxygen maybe. What are we doing with the waste? How is all this managed before the placenta is the onsite perfect and all powerful fetal growth manager in a word, womb milk, or histotroph

This is the subject of today's episode.

To contact me with questions or suggestions, find me at:

makingsenseofpregnancy@yahoo.com or @makingsenseofpregnancy