Making Sense of Pregnancy: What Experts Want you To Know About Your Body

 Every human enters the world through a pregnancy that either ends with a vaginal delivery or a C-section. So every human on the planet has been through birth.  technically speaking. Given that shared experience, it seems like birth, the how and the how long of it, would be a topic with a lot of relevance to many, many, if not all people. And, that maybe, we would understand what triggers labor and how to measure it's progress.

But to date, there are lots of holes in our understanding of this critical process. What initiates spontaneous labor? What should labor look like? When does it officially start? How long should each stage last? These questions are really important, because they inform doctors about what to expect and how to manage labor. In today's solo episode, I try to walk us through current theories of the how and the how long of birth.

Previous episodes about triggers for labor:

Dr. Christina Herrera talks about the placental clock and how it relates to preterm birth: https://podcasts.apple.com/us/podcast/using-the-placental-clock-to-predict-preterm-birth/id1779600854?i=1000702829834
Dr. Roger Young talks about how electricity moves through the uterus in active labor: https://podcasts.apple.com/us/podcast/how-new-research-on-uterine-contractions-could-revolutionize/id1779600854?i=1000681642524
Dr. Yong Wang talks about how we can measure the electricity that moves through a contracting uterus:https://podcasts.apple.com/us/podcast/understanding-how-uterine-contractions-work-a-key/id1779600854?i=1000691330103
Dr. Polina Lishko talks about the electricity of labor at the cellular level: https://podcasts.apple.com/us/podcast/turning-labor-on-and-off-the-identification/id1779600854?i=1000713382865

 Today I'm gonna share an episode that was originally aired about a year and a half ago about what might be the trigger for starting spontaneous labor. It's kind of amazing that this fundamental experience that all of us have starts with an event that arrives by surprise. In fact, we accept that , labor, if it starts when it starts, will be a surprise. Every popular depiction of a woman in labor that you've seen on TV or in movies or experienced yourself contains at least one real truth. The start of labor is a surprise. It's a surprise because despite the many things we know about labor, we don't know how or why it's initiated, what series of things have to happen to get labor to turn on, and why. In 1 in 10 births in the U. S., does it turn on too early? This is the topic my guest, Dr. Todd Rosen, talks about today. Collaborator, Bingbing Wang, have developed a compelling theory about the conversation between the placenta and the fetus. That may explain what these triggers are.

 We are at the cusp of understanding more about the complicated conversation going on between your brain, ovaries, and pituitary. Your menstrual cycle contains within it information about your overall health, and the work we'll talk about today gets us one step closer to deciphering important elements of this conversation. 

In particular, by organizing data according to the rhythm of menstrual cycles, we are looking not only at a level change, for example, is temperature going up or down in different parts of the cycle, but at the daily context in which temperature changes, which allows us to look for patterns in this change over time.

In the future, we may be able to use these patterns to diagnose not only issues with reproductive health (ie, PMDD, endometriosis, etc.), but with health overall.

Identifying Menstrual Metrics as Personal Health Markers: Age Trends and Individual Footprints in Temperature across 5674 cycles: https://www.science.org/doi/10.1126/sciadv.aeb1175

Nanotechnology looking at measuring hormones: https://www.nature.com/articles/s41565-023-01513-0

Your menstrual cycle is the engine of reproduction and a window into your overall health. 

It's critical both for a successful pregnancy, and can tell us things about your endocrine, metabolic, immune, and cardiac systems. 

We have tended to look at things like how heavy or light the flow of your period is, or the length of the cycle as signs of wellness or distress in your system. But some researchers, like the one I speak with today, are trying to mine different aspects of the cycle for information about overall health. 

What Dr. Gombert-Labedens  and her colleagues are looking at is menstrual cycle linked temperature patterns, which change systemically with age and are surprisingly consistent within each person, so that they may be useful to track aging and detect deviations from a person's usual physiological state. We'll talk today about the state of this research and where it may be going

Using activity trackers in pregnancy, conversation with Dr. Benjamin Smarr (part I): https://podcasts.apple.com/us/podcast/can-an-activity-tracker-tell-you-if-you-are-pregnant/id1779600854?i=1000719761885

Science Advances paper: Identifying Menstrual Metrics as Personal Health Markers: Age Trends and individual footprints in temperature across 5675 cycles: https://www.science.org/doi/10.1126/sciadv.aeb1175

 This is a glimpse of our future through the lens of the menstrual cycle. Women, on average, experience about 400 cycles in their lives, and the process is integrally connected to many other features of your overall health and, of course, is critically important to a successful pregnancy. Using 3-D human organoids, Dr. Turco and her team test different facets of the cells of the uterine lining to learn more about what in the world is going on in your uterus during your cycle. 

 In most studies of the human body, there's one particular market served by the research, but this one's a doozy. If you are a human with a uterus, this work is for you, and if you are planning to be born from a human with a uterus, this work is also for you. 

 For all recorded time, the human menstrual cycle has been kind of a mystery. Is your period too long? Is your period too short? Are you bleeding too much? Is there too much pain? 

It's hard to answer these questions because I'm not sure it makes sense to compare yourself to some, quote, "average woman," because the menstrual cycle is so integrally involved in so many different systems in your body. It makes more sense to look at how your cycle is changing over time, but we don't even have very much data about that. 

Can we experiment with mice? Sure. But our system is different from the system of a mouse. 

Can we look at samples of the uterine linings of different women over time? Sure. But that approach tells a story that's not the same as whatever is going on in one person's uterus over time. 

Today's guest is ushering in a new era of uterine lining exploration that will allow for a much more dynamic, human-centered examination of this amazing tissue that's critical for both a successful pregnancy and integral to women's health. She is opening up the black box of the human menstrual cycle. 

 Your menstrual cycle is incredibly important for your overall health and for your best chance at a successful pregnancy. 

Creating a high-tech uterine lining each month that you will either continue to develop through a pregnancy or you'll eliminate if pregnancy isn't on the menu, is a biologically intensive and complex process. And there are a select few among all placental mammals who run this process the way humans do. Scientists estimate that less than 2% of placental mammals menstruate the way we do. Something like 84 species out of more than 5,000. All the primate species are relatively closely related, and we menstruate in a similar way, but there's also unexpected attendance at this intimate gathering of placental mammals that menstruate like us, including the spiny mouse, some species of bat, and the elephant shrew. 

This week's topic is focused on why we essentially organize so many bodily functions around the way that we have a menstrual cycle, how on God's green earth we do it, and what information we can glean from keeping track of cycle to cycle variation.

 In many things in life, timing matters. 

That's also true in labor. 

If we can align when we induce labor with what's known about the circadian rhythms of our body, we may be able to take advantage of times at which our bodies are more receptive to these interventions, and turn that advantage into shorter labors or fewer C-sections.

Based on this retrospective study, these outcomes came with no costs to the newborns. Today we talk about some of the details of this work, how circadian rhythms show up in different ways for women of different weights, and what might be driving the induction impacts in the first stage of labor.

 If I told you that I've heard of a free way  to reduce the length of labor, to reduce the C-section rate for those most at risk of a C section, all without increasing the risk for the baby, you'd likely tell me to sell my magic beans to someone else. 

But labor and delivery do not arrive in a uniform way at all hours of the day. In fact, spontaneous labors tend to occur at night, with birth in the early hours of the morning. Using this fact, the researchers I speak with in this episode share what they found by dissecting the time of day into 1 hour slots to measure how the starting time of induction impacts labor outcomes like duration and mode of delivery.  It turns out that timing can have dramatic effects on these outcomes--which may significantly impact a mother's experience of birth.

Time of Day of Induction Impacts the Total Duration of Labor: https://www.ajogmfm.org/article/S2589-9333(26)00009-1/fulltext

 Miscarriage is very much a part of pregnancy. It's really common. Roughly 20% of implanted embryos are estimated to miscarry. 

Unfortunately, stillbirth is also part of the process. The odds are 1 in 175. 

But for most women who experience these outcomes, it feels like a shock, something you couldn't imagine would happen. In today's episode, I continue my conversation with Dr. Harvey Kliman, who explains why miscarriage and stillbirths happen and offers ways we can try to understand and mitigate the situation.

Find the paper and the density plot here, too:

Placenal Pathology Findings in Unexplained Pregnancy Loss: https://pmc.ncbi.nlm.nih.gov/articles/PMC10827979/