Talk:Gestational age

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This article needs one or more references to cover the content, added the tag. --FloNight 04:08, 23 November 2005 (UTC)

It how has eight references, so I've removed the tag. NCdave (talk) 18:03, 16 March 2008 (UTC)

ways to estimate[edit]

I dont think you understand this list. These are ways to judge the gestational age of a newborn baby that have been widely used in medical practice in the last 50 years. I do not understand how a woman's ability to guess when she might be ovulating makes it possible to judge a gestational age many months later to the degree that simply knowing the LMP provides. At any rate, it has not been widely used. Where did you get this? alteripse 17:31, 4 Jun 2005 (UTC)

I got this from a Creighton-model NFP instructor, who did a great job of calculating the birthday of my second child. Time of ovulation will vary, and commonly there can be multiple ovulations within a single cycle. Assuming just one ovulation though, the timing is more closely related to the following period. The preceding period has little to do with it; using the preceding period is thus a doubly-crude way to estimate. Effectively you are estimating the time of the period that didn't arrive and then going back from there. Periods can be quite irregular for some women, causing the last-cycle method to be off by weeks. AlbertCahalan 18:05, 4 Jun 2005 (UTC)
In any case, this method is in use and it is quite accurate. You really shouldn't be so quick to revert. That's not nice behavior. AlbertCahalan 18:05, 4 Jun 2005 (UTC)
To clarify a bit: Observation of cervical mucous will let you know ovulation to within a couple days. Ovulation happens at a relatively fixed offset from the following period, though accuracy is probably already worse than the cervical mucous observations. Problem is, that period is the one that never happened. You'll have to guess. You're not doing too bad if the woman has standard-sized periods like clockwork, but who ever has that? Lots of women have 3-week and 5-week periods, sometimes even longer. Many women have irregular periods. Ovulation does not occur at a very predictable time from the previous period. (thus making cervical mucous observations far more accurate for pregnancy control -- temperature works OK too) AlbertCahalan 18:15, 4 Jun 2005 (UTC)

Your method is basically a way to know probable date of conception. I suppose we could turn this article into a list of unusual ways for a mother to know when a baby was conceived (i.e., the date father was home on leave, or the date of the credit card charge for the fancy dinner after which, or the date of the police report of the rape, or the date of the ovulation induction injection, or the date of the artificial insemination, etc...), but I think it would be a better article if we don't. In actual practice, in the middle of a pregnancy or when a baby is born, the common ways that gestational age is estimated or corroborated are by LMP, u/s, or maturational exam, none of which are perfect. Apples and oranges. Sorry you thought it was rude, that was why I went to the talk page second time. alteripse 18:34, 4 Jun 2005 (UTC)

Well, you already covered "date father was home on leave" and so on. That's the first and obvious thing, the time of sexual intercourse. Alone, that says nothing unless the mother only ever had sex once. So some idea of ovulation should be used. The date of last period is one very common and crude way to narrow this down. Many women can't do any better, and some don't even track periods well. Look at this chart though. Clearly, using the last period is a poor way to guess. You could be off by weeks! Ultrasound seems to be about as bad as LMP. Cervical mucous observations alone will pin down ovulation to a couple days generally, which would be the accuracy if unfertilized eggs didn't live as long as they do. Temperature might be accurate too. AlbertCahalan 19:01, 4 Jun 2005 (UTC)

I'm not trying to be rude, but you are missing the point: once the probable date of conception is known by any method, estimating gestational age is trivial. Your method is one of an infinite number of ways a woman might know when she got pregnant. All of them are equivalent to "mother's knowledge of date of conception" and perhaps we should change item 1 in the list to say "probable date of conception" instead of "probable date of intercourse". Would you then feel that your method was included? The whole point of the initial version of the list was that a woman often does not know exactly when she conceived. There are then 3 commonly used ways of guessing how far along the pregnancy is, or how mature the fetus or newborn is: LMP, u/s, exam of infant. While each is obviously imperfect and has sources of error, these are still the commonly used ways of judging gest age if a woman doesn't know when she got pregnant. Do you get it now? alteripse 19:26, 4 Jun 2005 (UTC)

If you want to organize the list that way, then u/s is equivalent to examination. You could do like this:
  • date of conception
    • date of sexual intercourse
    • ovulation estimate
      • by temperature
      • by cervical mucous
      • by date of last period
  • observation of baby
    • by ultrasound
      • early and tolerably accurate
      • late and very inaccurate
    • after baby is born
  • date bounded by implantation
    • pregnancy test
    • implantation bleeding
  • IVF
One could argue that all methods are a way to estimate the date of conception though. That's really what gestational age is all about. So that leaves top-level items as follows:
  • date of insemination (police report, credit card bill, wedding day...)
  • ovulation estimate (temperature, mucous, last period...)
  • observation of baby (before or after birth)
  • implantation (pregnancy test, bleeding...)
  • IVF
Perhaps each of these should be a section.
AlbertCahalan 20:01, 4 Jun 2005 (UTC)

Gestational age vs. LMP[edit]

I have always read that gestational age is the age from conception (which this article states), and thus is, on average, two weeks shorter than the pregnancy length from last menstrual period (LMP). This article also states that an average pregnancy has a gestation of 40 weeks - I thought this was the average time from LMP, making the actual gestational period 38 weeks?

Looks like someone went ahead and made that distinction, changing the gestational period to 38 weeks. I just changed the parenthetical note from 280 days to 260 days, accordingly. Unfortunately though, this leaves the chart presented in the article mismatched with the actual article test, since the chart seems to be using LMP for its "gestational age". Mwelch 22:25, 8 May 2006 (UTC)

This article is the only place I can find Gestational Age defined as age from conception:

Gestational age is the time measured from the first day of the woman's last menstrual cycle to the current date and is measured in weeks. A pregnancy of normal gestation is approximately 40 weeks, with a normal range of 38 to 42 weeks.


Gestational age is the number of weeks and days a fetus has developed since the beginning of the pregnancy, or gestation. A pregnancy is formally considered as beginning on the first day of the mother's last menstrual period (LMP).

American Pregnancy Association-

Gestational age, or the age of the baby, is calculated from the first day of the mother's last menstrual period.

I'm not an expert by any means so I won't change the actual article but I am interested in the discrepancy.

In fact, the wikipedia page on pregnancy doesn't even define gestational age this way

That's interesting. As far as I am aware, gestational age is the only term that can be used when LMP is known to be inaccurate - the woman has unusally long or short cycles, for example, or conceived before her first post-partum menstruation. I have also seen the "LMP minus two weeks" definition of gestational age used on pro-life sites, to make more developed-looking embryos/fetuses sound younger than they actually are. And number of weeks and days a fetus has developed since the beginning of the pregnancy is pretty ambiguous, see Beginning of pregnancy controversy.
But you appear to be right, in that it is also used interchangably with LMP. So there are two definitions, and the article needs to be changed to reflect that. Feel free to do so. Lyrl 21:44, 19 June 2006 (UTC)

3rd sentence, conceptional age and CFN[edit]

I propose removing the 3rd sentence. The source itself says "The term "conceptual age" is incorrect and should not be used," and goes on to say the situation where 'conception' or implantation is known is assisted fertilization. In the US, IVF only accounts for 1% of births. This sentence is confusing and unnecessary. Anyway, normally it is the other way around: you can estimate the date of fertilization and implantation based on the LMP. I'd say we should replace the sentence with "Gestational age is approximately 2 weeks older than when fertilization took place". -Andrew c 02:46, 31 January 2007 (UTC)

There are more than 28,000 Google hits for "conceptional age". The cited article merely says that the term “conceptional age” should not be used in clinical pediatrics. It doesn’t say the term should never be used anywhere. As we all know, the conceptional age (or age from conception or fertilization) is very very often used. There's absolutely no harm in explaining that this age is offset two weeks from the "geatational" or "menstrual" age, and in fact this explanation is very useful. That's why the cited article does so.Ferrylodge 02:58, 31 January 2007 (UTC)
IVF isn't the only or most common method of assisted reproduction - women on Clomid, injectables, and/or doing IUI will frequently be monitored by ultrasound. Ovulation predictor kits are used by large numbers of women. Not sure how common using fertility awareness is to acheive pregnancy (certainly more common than the 0.2% of Americans who use it to avoid pregnancy). Combined, I believe these different practices provide a significant number of women with an estimated date of fertilization other than (and more accurate than) the LMP. So, to me, explaining that gestational age is calculated beginning two weeks prior to fertilization is relevant. Though I do see (and agree with) the objection to the current wording. I'll think about alternative wording. Lyrl Talk C 03:14, 31 January 2007 (UTC)
How about: "Gestational age is approximately 2 weeks older than conceptional age"?
Incidentally, the term "fetal age" gets about 89,000 Google hits, and the term "developmental age" gets around 240,000 hits. Conceptional age, and developmental age, and fetal age, and fertilization age, are all pretty much synonymous. My primary concern is that this article should not leave the impression that prenatal age is only measured from two weeks prior to conception, when in fact it's very often measured from fertilization.Ferrylodge 03:39, 31 January 2007 (UTC)
I like your proposed wording. I think it is important to mention both concepts, and because both concepts are used. The CFN citation believes that it can get very confusing with the 2 week difference, so they prefer to use the LMP gestational age always in obstetrics. But again that is just one source, in the Embryology text we covered in another article (I believe it was the beginning of pregnancy controversy article) they prefer to use developmental age presumably because the focus isn't on the person who is pregnant, but instead on the thing actually developing. Anyway, thank you for considering the changes and suggesting something workable!-Andrew c 16:25, 31 January 2007 (UTC)

Some changes[edit]

After some discussion with two MD's, I corrected the three following points because I think they are against what is said in the references mentioned. (I think it's important to note that this is only a definition, not realy an "age".)

  • 1. The references clearly state that gestational age IS NOT the "age of an embryo or fetus (or newborn infant)", but the time elapsed since the first day of the last menstrual period. So it’s always longer then that age (more or less two weeks).
  • 2. The developmental age results from the doctor’s evaluation of the development of the new born and it IS NOT calculated as two weeks less than the gestational age. ( the example given in [1] is about a premature baby that could be evaluated as having a development of 38 weeks instead of 36 weeks of gestational age-it was an example not a formula).
  • 3. I never heard of any controversy as to what is "gestational age" and it’s clear for me that this "age" is always longer then the time of pregnancy (either defined as time of the implantation or the time of fertilization(the formation of a viable zygote)). So I think that it would be unnecessary to make any reference inn this article about that controversy. However I only rephrased it to reflect this idea. AntoniusJ 13:08, 18 February 2007 (UTC)
Gestational age... is the time elapsed between the first day of the last normal menstrual period and the day of delivery.
First, not if a woman ovulated on day 42 of her menstrual cycle. I believe some qualifier needs to be put on this statement.
Second, if I understand correctly, gestational age is commonly used to measure pregnancy length during pregnancy. A fetus can have a gestational age of 12 weeks without having been miscarried, right? Lyrl Talk C 21:32, 18 February 2007 (UTC)
This article defines the length of a full-term human pregnancy. While it may be obvious to Antonius that pregnancy begins on a woman's first day of menstrual bleeding, I'm not convinced this is obvious to everybody. I think it is worth noting that this article uses menstruation as the marker of pregnancy onset, to distinguish from pregnancy beginning at fertilization which is also a common belief. Lyrl Talk C 14:23, 18 February 2007 (UTC)
AntoniusJ, you say that "gestational age IS NOT the age of an embryo or fetus." I agree. What type of age would you call the age of an embryo or fetus? There are several possibilities (e.g. fertilization age, conceptional age, fetal age, and developmental age). At least one of those possibilities ought to be mentioned in the article. As explained above, my primary concern is that this article should not leave the impression that age is only measured from two weeks prior to conception. As Andrew C. mentioned above, "it is important to mention both concepts." Therefore, unless you object, I will revise the article to clarify that age of the embryo or fetus (e.g. fertilization age or developmental age) is distinct from (and should not be confused with) gestational age.Ferrylodge 19:21, 18 February 2007 (UTC)

I still think the article begins with an error.

  • 1- I thought it was clear for all that gestational age is always greater than the age of the fetus(More or less two weeks). That is the question. To state that it is the age of the fetus is clearly wrong(Please show me some scientific source that says the contrary).Here [[2]] you'll see that the age of the fetus is what they call "Gestation" and they distinguish it from "Gestational age".
  • 2-The beginning of pregnancy is another question. I personally doubt that the pregnancy begins when gestation age begins to be counted.(as far as I know gestation age is used just because it is more “easy” to know exactly when it started) . But I think the question of when pregnancy begins as nothing to do with this definition.
  • 3- Developmental age-If you see [3] instead of “Free dicionaray” you’ll see that “This may not match the calendar gestational age. For example, an infant born with a gestational age of 36 weeks may actually have a developmental gestational age of 38 weeks, and therefore behave more like a full-term infant than a premature infant.”AntoniusJ 02:16, 20 February 2007 (UTC)
AntoniusJ, it may be helpful for people following this discussion to take note that your two links are the same item. Also, let's excerpt the relevant parts of that item:
"Gestation is the period of time between conception and birth, during which the fetus grows and develops inside its mother's uterus. Gestational age is the time measured from the first day of the woman's last menstrual cycle to the current date. It is measured in weeks. A pregnancy of normal gestation is approximately 40 weeks, with a normal range of 38 to 42 weeks. Infants born before 37 weeks are considered premature. Infants born after 42 weeks are considered postmature. This gestational maturity rating is measured by the Ballard scale or Dubowitz exam. Strictly speaking, the gestational age of a fetus or infant is a measurement of time inside of the uterus. Gestational age can be determined before the baby is born or at its birth. Prior to birth, growth is determined with ultrasound by measuring the diameter of the head and comparing the head circumference and the abdominal circumference. Following birth, assessing an infant's weight, length, head circumference, condition of skin and hair, reflexes, muscle tone, posture, and vital signs can provide a 'developmental' gestational age. This may not match the calendar gestational age. For example, an infant born with a gestational age of 36 weeks may actually have a developmental gestational age of 38 weeks, and therefore behave more like a full-term infant than a premature infant. Determination of gestational age is important, because it provides valuable information regarding expected or potential problems and directly affects the medical treatment plan for the baby."
I have put in bold italics the part that you quoted. It seems to me that KillerChihuahua has interpreted this correctly. Please note that the present article mentions "fertilization age" rather than "developmental age". "Gestation" is the whole period of time from conception to birth. In contrast, "gestational age" is the time that has elapsed since the first day of a woman's last menstrual cycle. And, "fertilization age" is the time that has elapsed since fertilization. The concept of "developmental age" seems to be a bit fuzzier, and therefore it has been (wisely) left out of the article. The current article says that the gestational age is always greater than the fertilization age. So, what's the problem?Ferrylodge 02:31, 20 February 2007 (UTC)
No problem at all. Now I think the article it's better than it was before, although a little bit confuse("the age of a foetus since the LMP"-in the LMP the foetus doesn't exists yet-everybody agrees on that ). ( and is there anything against calling the same link twice in two different phrases ? ) AntoniusJ 00:31, 24 February 2007 (UTC)
I assume you're referring to the redundant wikilink to fetus. I've just fixed that. Thx.Ferrylodge 17:10, 24 February 2007 (UTC)

Corrected gestational age?[edit]

I like the intro quite a bit now. Nice work to everyone who has been contributing.

My remaining concern is with the section The gestational age of an individual infant can be more accurately estimated from:, which contradicts the opening statement that gestational age is always calculated from LMP. Maybe that second section needs to be edited to talk about "adjusting" gestational age, instead of "more accurately estimating"? I'm not confident enough in how the term is used medically to make the edits myself. Lyrl Talk C 00:31, 21 February 2007 (UTC)

Regarding the last sentence: "The gestational age of children conceived by in vitro fertilization is known to the hour" Don't you mean the developmental age? since the LMP would be known "to the hour" in both cases or, not known in the "in-vitro" case if the patient has hormonal or other cause for menstrual irregularities (cause of infertility)—The preceding unsigned comment was added by (talkcontribs) 16:13, 17 July 2007.

Two definitions of gestational age[edit]

There are two definitions of "gestational age" in common use:

  • Stedman's Online Medical Dictionary, 27th Edition says "n. 1. in embryology, the age of a conceptus expressed in elapsed time since conception; 2. in obstetrics, the developmental age of a fetus, usually based on the presumed first day of the last normal menstrual period."

Stedman's is the best I've found.

Unfortunately, the current Wikipedia article gives only the obstetricians' definition. The embryologists' definition, which counts gestational age as the age from conception/fertilization, is at least as commonly used.

Worse yet, the current Wikipedia article says the embryologists' definition is wrong: "The gestational age should not be confused with the fertilization age..."

Here are some more online dictionary definitions. Some use the obstetricians' definition, more use the embryologists' definition, and some confuse the two:

  • The British On-line Medical Dictionary says "<obstetrics> Foetal age of a newborn, calculated from the number of completed weeks since the first day of the mother's last menstrual period to the date of birth."
  • Medline is just a mess. It confuses the two definitions, thus effectively defining conception as the first day of the mother's last menstrual period! "Gestation is the period of time between conception and birth during which the fetus grows and develops inside the mother's womb. Gestational age is the time measured from the first day of the woman's last menstrual cycle to the current date. It is measured in weeks. A pregnancy of normal gestation is approximately 40 weeks, with a normal range of 38 to 42 weeks..."

The bottom line is that if an obstetrician uses the term "gestational age" he probably means from LMP, but most others use the term as a synonym for fertilization age. This article needs to be fixed to reflect the fact that there are actually two different definitions in common use. NCdave (talk) 16:38, 15 March 2008 (UTC)

Beg to differ re "in common use" - I can promise you every pregnant woman in UK, US, Canada, Australia etc has their gestational status based on time from LMP (or equivalent date if menstrual cycle significantly different from 28-days or in case IVF etc). As such, all of us were born with expected dates calculated 40 weeks after our mother's LMPs and this is overwhelmingly the commonest use. Now I do not dispute one can refer to a fetus by number of weeks of development since fertilisation, but this is not the commonest system used and is therefore a lesser used system, not withstanding dictionairies not being precise or acurate in their descriptions of scientific terminology (go look up baby, neonate, infant or even human for idiosyncratic definitions). Likewise any reports on definitions of age of viability are stated in gestational age from LMP, and restrictions in the UK on permitted abortions are defined as before 24 weeks from the LMP. David Ruben Talk 17:00, 15 March 2008 (UTC)
I've adjusted the article to reflect the two definitions, and listed the obstetrics definition first. I also added several additional references. What do you think of it? NCdave (talk) 17:32, 15 March 2008 (UTC)
When you talk about a "pregnant woman's gestational status" the context is human obstetrics, not embryology.
Most people thinks that the definition of a term used in their context of interest, or their field, is the definition. For another example, try talking to people in various fields about the word "organic." A chemist or physicist will tell you that it simply means a compound containing carbon & hydrogen. A biologist will tell you that it means something derived from a living organism. A farmer or grocer will tell you that it refers to a food which was produced without the aid of pesticides or commercial fertilizers. Many of them will tell you in all seriousness that their definition is the correct definition, and the other definitions (if they've heard of them at all) represent misuse of the term. NCdave (talk) 18:01, 16 March 2008 (UTC)
I agree on your points, although I think the assumption can safely be had that wikipedia articles as a default are most likely be interpreted with respect to us humans (hence myocardial infarction will describe as symptoms referred pain into left arm rather than left forlimb). Hence half the world's population (of humans) experience of gestation will involve antenatal care/services... That said, your edit is well written, clear and nicely phrased - well done :-) David Ruben Talk 01:41, 17 March 2008 (UTC)

odd infobar figure[edit]

This article is about "gestation age", the infobar contains a figure with definitions for "Birth weight and gestational age", the definitions all correspond to different birth weights. This kind of information is not really specifically about "gestational age", and is kind of distracting. Is there a better figure which sums up "gestational age" (especially since there are so many different definitions associated with "gestational age") and does NOT include birth weights? Or should the article focus on (and be retitled to) "gestational age and birth weight"? -- (talk) 16:38, 26 January 2012 (UTC)

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