Maternity - L&D, part 2: Factors Affecting Labor, Fetal Position, Fetal Station
by Meris Shuwarger BSN, RN, CEN, TCRN September 18, 2021 Updated: June 16, 2022 8 min read
This article focuses on factors affecting labor, especially fetal position and fetal station. The Maternity Nursing series follows along with our Maternity Nursing Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
When you see this Cool Chicken, that indicates one of Cathy's silly mnemonics to help you remember. The Cool Chicken hints in these articles are just a taste of what's available across our Level Up RN Flashcards for nursing students!
Factors affecting labor
When considering the factors affecting labor, we use a shorthand: the 3Ps: the passageway, the powers, and the passenger.
3Ps in a Pod: Passageway, Powers, Passenger!
The passageway is another name for the birth canal (comprising the cervix, vagina, and pelvis), and concerns the patient’s anatomy. Is their pelvis tilted? How is their cervix? These anatomical considerations may affect a patient’s ability to birth a baby vaginally or alter the labor in some other way.
Powers refers to contractions. How strong are the contractions, and how are they affecting the cervix? If contractions are ineffective — if they don’t change the cervix in preparation for labor — it’s possible that the passageway is inadequate, and this will affect the patient's ability to give birth.
The passenger is the fetus (and the placenta). The following factors will affect labor: fetal head, fetal lie, fetal presentation, and fetal attitude. Two other key elements of labor include fetal position and fetal station, which are discussed in more detail below.
Fetal head describes both the size and molding, or shape, of the fetus’s head.
Head molding refers to changes in shape of the fetus’s head as it experiences pressure during the journey through the birth canal. A tight birth canal may result in squeezing the fetus’s head into a slightly oblong shape, a common occurrence that usually disappears in the days after birth.
Fetal lie describes how the fetus is positioned in the womb. It may be longitudinal, transverse, or oblique.
- Longitudinal: in a longitudinal lie, the fetus’s spine runs in the same direction (parallel) as the mother’s spine.
- Transverse: in a transverse lie, the fetus is positioned horizontally across the uterus, rather than vertically.
- Oblique: in an oblique lie, the fetus’s head is against the mother’s hip, high above the birth canal, with no part of the fetus’s body pressing against the cervix.
Fetal presentation is the first part of the fetus to enter the pelvic inlet. It may be the head, the chin, a shoulder, or the fetus may be presenting as breech (emerging feet-first).
Fetal attitude describes the relationship of fetus’s body parts to one another, described as either flexed or extended:
- Fetal flexion is when the fetus’s chin is tucked close to its chest, and the other limbs are similarly tucked, which makes it easier for the fetus to pass through the pelvis.
- Fetal extension is the position of the fetus during labor and delivery, where the head is extended back.
Fetal position, as the name suggests, describes how the fetus is positioned in the womb and how it will present (which part of the baby emerges first).
The fetus may be positioned in any number of ways, so a three-letter label is assigned to clarify the position. Note that the direction of the fetus’s back determines its relative position.
The first letter is either “L” or “R”" that is “left” or “right.” Is the fetus oriented toward the left or right?
The second letter describes which part of the baby is about to present in the pelvis: “O” (occiput or head-first), “S” (sacrum or butt-first), “M” (mentum or chin-first), or “Sc” (scapula or arm- or shoulder-first).
The third letter describes the direction the fetus is facing, relative to the mother: “A” (anterior, facing forward), “P” (posterior, facing backward), or “T” (transverse, lying on its side — horizontally across the uterus).
The optimal fetal position is LOA: left, occiput, anterior. In this situation, the fetus is positioned so that the occiput (head) will emerge first; the fetus is angled toward the left side of the mother’s pelvis and is facing the mother’s front (anterior). This position is usually preferred for a well-facilitated birth.
Different positions will result in different birth experiences for mother and baby.
Fetal station refers to how far has the head or presenting part descended into the pelvis.
Station zero means at the level of the ischial spines, the narrowest part of the mother’s pelvis. At station zero, the fetus is said to be “engaged.”
If the fetus is stationed higher up, that is designated a negative number. If stationed lower (closer to the vaginal opening), that is designated a positive number.
A negative-3, for example, indicates the baby is not at an optimal station for delivery. At plus-3, the baby is on its way!
Hi, I'm Meris, and in this video, I'm going to be talking to you about the factors affecting labor along with the fetal position and fetal station. I'm going to be following along using our maternity flashcards. These are available on our website, leveluprn.com, if you want to grab a set for yourself, but if you already have a set, I would invite you to follow along with me. Okay, let's get started.
So first up, we are talking about the factors affecting labor, and you will see on the back of the card that we have a cool chicken hint here to help you remember these different factors. We say there's three peas and a pod. So the three p's here are going to be the passageway, the powers, and the passenger.
So the passageway is just the birth canal, right? It's about the anatomy. Is a patient's pelvis tilted? How is the cervix? That sort of the thing. All of those anatomical considerations can change are a patient's ability to birth a baby vaginally or can change what needs to happen during labor.
Then we have the powers, and the powers refer to the contractions. How strong are the contractions? How effectively are they affecting the cervix? All of those things. Again, if we have ineffective change to the cervix, then we're not going to have an adequate passageway and we're not going to be able to give birth, right? So when we talk about the powers, we're talking about how the contractions are affecting the cervix.
And then you'll see here that for passenger we're talking about the fetus, and there's a whole lot of information on here. I'll let you read it for yourself; we're going to talk about a bunch of it. But there's one thing that I really want to pull out of here, and this is going to be the fetal position and fetal station. We're going to talk about it with the next cards because we have nice illustrations for you. But I do want to talk about them because it it gets a little bit confusing.
So when we talk about fetal position, we are using three letters to describe it. So this is actually going to be this drawing right here. Sorry, I couldn't remember which side it was on. This is the drawing that you'll see in the next card. I think it is beautiful, and I think that it is one of the best illustrations that exist to talk about how the fetus is actually positioned.
So when we have these three letters, the first letter is either L or R, so it's saying left or right, and then the middle is going to be saying what part of the baby are we talking about, right?
So we can be talking about occiput, meaning the back of the head. We can be talking about mentum, meaning the chin. We could also have things like scapula, which we would say SC. We could have sacrum, which would be just an S. So what part of the body are we talking about is presenting in the pelvis. And then the last abbreviation in that three letters is going to describe where it is. So this is going to be either anterior, posterior, or transverse.
So let me give you an example. If we say that the baby is LOA, that means that the baby is positioned so that the occiput, the middle there, is left for the patient, for the mother, and anterior.
So if you look at the next card - and you can actually see this illustration, and I'll bring it in close for you and hopefully it will focus here - If you see that, you can see what I'm talking about, about how the baby is positioned. And in this instance here, we are talking all about the occiput. So it gets a little bit confusing because we could have mental presentation. We could have the scapula presenting. But for this illustration, we're talking just about the occiput. So what is the optimal positioning for this fetus? Well, the optimal is going to be LOA, left occiput anterior. That is what we would prefer to have a really well-facilitated birth.
So I remember this as LOA is okay. That's how I remembered it. It's not on our card or anything, but that's kind of the easiest way to remember it. But if I had to choose, then I would say ROA would be second best.
What we don't want is a P at the end there. We don't want the occiput, the baby's back of their head, to be facing posterior of mom, meaning the back of the baby's head is facing mom's back, because this is that sunny side up delivery. And with that sunny side up delivery, we can have a lot of pain, a lot of complications there. So LOA is okay. That's going to be the best way for that baby to be born. And so, again, I really want you to take the time to look at this illustration in-depth. I love this illustration so much that I have it on my wall. I just think it is really, really good at sort of explaining what all of these mean. Of course, only talking about the occiput presentation.
Now, lastly, we're going to talk about fetal station. So when we talk about station, it basically just means how far has the head or presenting part descended into the pelvis. So station zero means at the level of the ischial spines. Anything higher up than that is going to have a negative number. Anything lower, like closer to the vaginal opening, is going to have a positive number. You can remember this because plus four is on the floor. So if you can remember plus four on the floor, then you can remember that the positive station means that the baby is exiting closer to the exit of the pelvis.
Now, here is a really nice illustration. Again, I just think that the illustrations in this deck are beautiful and so helpful. So you can see here that we have a baby in the pelvis and we're demonstrating where the baby is and then what each station is. So currently this baby is at negative three station. That's not really an optimal station for delivery. I'm not thinking this baby's coming out imminently, right? Now. If I had plus three, I'm thinking, "This baby is about to enter the world."
So just important to remember, positive numbers mean closer to the exit of the pelvis, closer to being in the vagina, right? So plus four on the floor.
Okay. So let's test your knowledge. If I said that you checked the patient and they were presenting ROP, what does that mean? Next question, what is the optimal presentation for the fetus for a well-facilitated birth? And last question, if I have a baby who is at the level of the ischial spines, what station are they at?
All right. I hope that review is helpful, and I really hope I get to see you in the next one. Thanks so much and happy studying.
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