Maternity - Pregnancy, part 3: GTPAL, Naegele's Rule, and Prenatal Labs/Diagnostics

August 30, 2021 Updated: October 26, 2021 11 min read

In this article, we'll cover GTPAL, which is how you classify a patient's pregnancies and births, how to estimate a patient's due date, and some important prenatal labs and diagnostics, including hCG, Rh factor, MSAFP and OGTT.

This 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.

Cool Chicken 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!


GTPAL is a measurement of the number of pregnancies and deliveries with different outcomes a patient has had. GTPAL stands for gravidity, term, preterm, abortion, and living.


Gravidity is a measure of the patient's total number of pregnancies, including their current pregnancy. The total Gravida number will include Term, Preterm, and Abortion.

Gravida terms

There are three terms used for gravida, which are nulligravida, primigravida, and multigravida.


Nulligravida means a patient has never been pregnant.


If a patient is primigravida that means they are on their first pregnancy. In your nursing career, you may hear something like "oh, she's a primi," which means that patient has not had a baby before. This is not to be confused with preemie, which is a slang term for a baby born prematurely.


If a patient is multigravida that means they have been pregnant multiple times, so two or more times.


The term number in GTPAL is how many full term births a patient has had, full term meaning delivered at 38 weeks or later.


The preterm number in GTPAL is how many preterm births a patient has had, preterm meaning the number of births from viability (~20 weeks) to 37 weeks.


Abortion is a general medical term meaning a pregnancy that has ended without a live birth, including induced (elective/therapeutic) abortions and spontaneous miscarriages. The abortion number in GTPAL is how many abortions total there have been.

As Meris notes in the video, to most people, the term abortion means induced abortion, so be cautious about the use of this term, especially around patients that have been through miscarriage or baby loss.


The living number in GTPAL represents how many living children the patient currently has. This number is independent of the other numbers, but would not exceed the combined total of Term and Preterm.

To clarify the meaning of living, imagine a patient lives to 120 years old and outlives all of their children. They may be G5 but L0.

GTPAL example calculation

Imagine a patient who has had 2 term deliveries, 1 preterm delivery, 7 miscarriages, and has 2 living children.

  • G = 10 (the patient's combined 2 term birth + 1 preterm birth + 7 miscarriages )
  • T = 2 (the patient's 2 term births)
  • P = 1 (the patient's 1 preterm births)
  • A = 7 (the patient's 7 miscarriages)
  • L = 2 (the patient's 2 living children)

To further clarify what GTPAL means and doesn't mean, notice that the patient had a total of 3 births, but only has 2 living children. This patient lost their child at some point, and based on the available data, the child may have died in infancy or died at age 20—we don't know.

Estimating due dates

When estimating a patient's due date, there are two methods you can follow. For both, you will start with the first day of the patient's last period.

Nagele's rule

Using Nagele's rule, you'll take the first day of the patient's last period, subtract 3 months, then add 1 week, then add one year.

Cathy's rule

Cathy's rule is a simplified version of Nagele's rule. You'll take the first day of the patient's last period, then add 9 months, then add 1 week.

Cathy's rule is the same as Nagele's, but the months calculation is condensed into one step. When Nagele has you subtract 3 months then add 12 months, it's the same thing as adding 9 months. Ostensibly, subtracting 3 and then adding 12 makes cross-year calculations easier, but many people find 9 months to be easiest.

Prenatal labs & diagnostics

The prenatal labs and diagnostics we'll cover here are hCG, Rh factor, MSAFP, and OGTT. In later videos, we'll cover diagnostics that are further along in the process, like an amniocentesis.


Human chorionic gonadotropin (hCG) is known as the pregnancy hormone, and it is what's detected in an over-the-counter pregnancy test. However, it's only a probable sign of pregnancy, not a positive one.

hCG may be low in cases of ectopic pregnancy and elevated in cases of molar pregnancy or multifetal pregnancy.

Rh factor

Rh factor is whether or not someone has Rh antigen in their blood. This text looks for maternal-fetal blood compatibility. In the Rh factor test, blood typing is done at the first prenatal visit to determine if the pregnant patient has Rh antigen on their red blood cells (is Rh-positive) or lacks the Rh antigen (is Rh-negative).

If an Rh-negative patient is pregnant with an Rh-positive baby, they are Rh incompatible, and the patient may develop antibodies to fight back against the Rh protein. Usually, this is not a problem on the first pregnancy. However, if left untreated, on the second pregnancy, the antibodies could cross the placenta and attack the baby's red blood cells, which is a process known as erythroblastosis fetalis.

Luckily, there is treatment available called Rhogam.

Erythroblastosis fetalis

Erythroblastosis fetalis is when a fetus's red blood cells are destroyed faster than they can be made, because maternal antibodies have crossed the placenta.


Rhogam, which is short for Rh immune globulin, is a medication that can be given to Rh-negative pregnant patients to help prevent them from developing antibodies against the Rh protein present in the blood of Rh-positive babies.

Rhogam is administered at 28 weeks and within 72 hours of delivery. Rhogam is also administered after any pelvic or abdominal trauma or vaginal bleeding, because these are occasions wherein the maternal blood may mix with the fetal blood.


Maternal serum alpha-fetoprotein (MSAFP) is a test for genetic abnormalities that is performed at 15 - 20 weeks gestation. High MSAFP may be indicative of neural tube defects. MSAFP may be indicative of Down syndrome.

Cool Chicken MSAFP will be down for Down syndrome.

As Meris points out in the video, it's important to note that MSAFP being high or low is not diagnostic in and of itself, and further testing is needed to determine if neural tube defects or Down syndrome is present.

Oral glucose tolerance test (OGTT)

The oral glucose tolerance test is a screening for gestational diabetes.

The one-hour OGTT is done at 24 - 28 weeks, and no fasting is required. The patient drinks 50 g glucose solution, and if their glucose levels are greater than 140 mg/dL one hour later, they must follow up with a three-hour OGTT.

A three-hour OGTT requires the patient to fast beforehand. Blood sugar is checked at fasting. Then the patient consumes a 100 g glucose solution. Then their blood sugar levels are tested after one hour, after two hours, and after three hours. If two or more of their results exceed the threshold, the patient is diagnosed with gestational diabetes.

Full Transcript

Hi, I'm Meris, and in this video, I'm going to be talking to you about the gravida and para numbers, Naegele's Rule for calculating estimated due date, and I'm also going to be talking to you about the different types of labs and diagnostics that are done during prenatal care. So I'm going to be following along using our maternity nursing flashcards. These are available on our website And if you already have a set of your own, I would absolutely invite you to follow along with me. So let's go ahead and get started.

We're going to be starting talking about GTPAL. These are the numbers used to represent how many pregnancies and different types of deliveries or outcomes that a patient has had.

So G stands for gravidy. Gravidy with a D, not a T. So gravid means pregnant. So gravidy means how many times has this patient been pregnant, no matter what the outcome? Okay? No matter what the outcome, how many times has this patient been pregnant? Then, we're moving on. So, G, gravidy, just talking about pregnancy. Now we're moving on to the para numbers. So this is how many times a patient has had different types of outcomes.

So term GT. T is for term. So the next number means how many term deliveries, meaning past 38 weeks, has this patient had.

Then, we move on to preterm. How many preterm births has this patient had? That's going to be from the age of viability, around 20-ish weeks, 24 weeks through 37 weeks. Okay. So how many times has this patient been pregnant? How many term deliveries? How many preterm deliveries?

The next one, the A in GTPAL, is abortions.

Now, keep in mind that abortion is a medical term, which means that a pregnancy has ended. It is not a term that means elective or therapeutic abortion, meaning something that was induced. It can mean that, but it can also refer to spontaneous miscarriages. I want to caution you to be very careful about how you use this word around patients, especially those who have had miscarriages or losses. We in the medical community may know that this just means the loss of a pregnancy, but your patient may not.

And then, the L means how many children are living now? Okay? So I'm going to do a quiz with you at the end. So see if you can calculate some GTPAL numbers.

And then gravida terms. Nulligravida means never been pregnant.

Primigravida means first pregnancy.

And then, multigravida means multiple pregnancies, two or more. So you will hear-- sometimes you'll see like, "Oh she's a primi," meaning she's never had a baby before. So just get to know those terms.

And then, moving on, we are talking about Naegele's Rule.

So Naegele was this guy who came up with the rule for how you calculate the estimated delivery date of a patient.

Now, the estimated gestational age in human beings is 40 weeks.

So Naegele said if you know the first date of the patient's last menstrual cycle,

subtract three months,

then add one week,

and then add one year.

It's very confusing. The point being, really what we're doing is we're getting nine months and one week in the future.

So we have Cathy's easier rule, which is add nine months and one week to whatever the patient's last menstrual period was. The first day of the last menstrual period is used to calculate this because it's 40 weeks from that date. So at conception, you're actually two weeks into the gestational cycle, if that makes sense.

All right. So, for example, if the first day of the last menses is April 1st of 2020,

Naegele says that you would subtract three months, which would make it January 1st, 2020, add one week, January 8th, 2020, and then add one year, January 8th, 2021.

Cathy's rule says April 1st, 2020. We're going to add nine months. That gives us January 1st, 2021. And then add another week, January 8th. All right.

Now, moving on, these last two cards are pretty hefty. Okay? There's a lot of information on them because it's super important in this class to understand what the testing is in pregnancy. It's very different from testing that you've learned about at any other time in the program.

So starting off, let's talk about HCG. This is human chorionic gonadotropin. It's the pregnancy hormone. This may or may not be done, and it just kind of depends on your patient. But it can be done.

Now, Rh factor. We talked about this in the last video. We have to know what the patient's blood type is.

We have to because if I am Rh-negative, and I have a baby who is Rh-positive, the first time, nothing is going to happen, probably. We're going to mix blood at delivery. And then, if I should ever become pregnant again in the future with an Rh-positive baby, my immune system is going to recognize that antigen as being foreign, as being a threat, and it is going to attack that baby in something called erythroblastosis fetalis. Okay? It's not a good thing. So we can end up with the baby dying because of this.

So if we take RhoGAM, which is an IM injection-- if we take RhoGAM, it's actually going to suppress that immune response so that we don't end up making those antibodies against the Rh factor. So you'll see here that we administered at 28 weeks - very, very important timing - but we also give it within 72 hours of delivery.

And then, any time there's some sort of pelvic or abdominal trauma or vaginal bleeding. Okay. Super important to know. So those were some labs.

MSAFP is another lab. MSAFP stands for maternal serum alpha-fetoprotein. So this means it's measured through the maternal serum, through the patient's blood, not through the fetus. And this helps to screen for some genetic abnormalities.

So an increased MSAFP is indicative of neural tube defects,

but a decrease in MSAFP can be indicative of a Down syndrome. And we do have our cool chicken here that MSAFP will be down in Down syndrome.

Now, it's important to note this is not diagnostic. It does not mean this is what's happening. MSAFP numbers can be off for a lot of reasons. So if we did get a high or a low result, then we would want to follow it up with an amniocentesis to confirm.

So then, the next thing on this card is the oral gestational-- I'm sorry, glucose tolerance test. So this is the gestational diabetes screening test. What this is, is going to be testing the patient's response to glucose to help us identify gestational diabetes.

So the one-hour glucose tolerance is the screening one that is done on all pregnant patients that consent to it, usually 24 to 48 weeks. No fasting is required. They're going to drink a 50-gram glucose solution. We're going to wait an hour, and we're going to draw their blood. If it is above 140, that's the magic number, 140, then we are going to move on to a three-hour glucose testing. If it's below 140, we say, "Good, you don't have gestational diabetes. You can carry on with your life." But if it's above that, then we're going to move on to the three-hour.

Now, with the three-hour, that's a fasting test. You have to arrive having had nothing to eat or drink except for water. And then they will give you 100 grams of glucose to drink. But before they do, they're going to draw your blood. So they're going to get a fasting level on you. Then, you're going to drink the stuff. Wait an hour. Then you're going to have a one-hour, a two-hour, and a three-hour blood test to see what your glucose was. 

Any two results being out of whack is diagnostic for gestational diabetes. So if I come in and my fasting level is a little high, but the one-, two-, and three-hour are good, it's fine. I don't have gestational diabetes. But if two, three, or four of them are elevated, then we are thinking, "Yep, this is gestational diabetes." So important to know those cutoffs so that you can help to better educate your patients.

All right. So that is it for the GTPAL, and also for the Naegele's Rule, and also some labs and diagnostics. I hope that was helpful. If it was, please like this video or leave me a comment so that I know. And you definitely want to subscribe so that you can be the first to know in the next video in the series drops. Thanks so much, and happy studying.

First, let me say, so I passed my one-hour glucose with my daughter, and my first baby, and that was great. And then, with my second one, I failed miserably, and I had to do the three-hour. And I passed, but I am a very hard stick. So it was a very treacherous and scary three hours. But, okay.

So let's do a GTPAL calculation.

So you have a patient who has had 2 live births.

She has had 2 term deliveries.

She has had 1 preterm delivery.

And she has had 7 miscarriages.

She currently has 2 living children.

So what is your GTPAL calculation for this patient? Go ahead. Pause it if you need to think about it. I'll be here when you're done.

So the G should be 10. Right?

So she had 2 live births-- 2 term deliveries-- I'm sorry.

A preterm delivery.

And then she had 7 miscarriages.

Right? So we have 10 total pregnancies.

And then, the T number should be 2. She had 2 term births.

The preterm, the P, should be 1.

She had 1 preterm birth.

And then the A, number of abortions, should be 7. She had 7 miscarriages.

And then the L number should be 2 because she only has 2 living children.

I hope that was helpful.

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