WordNet

the period during which an embryo develops (about 266 days in humans) (同)gestation period
the conception and development of an idea or plan
a structure resembling a bag in an animal
of or relating to gestation

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妊娠;妊娠期間 / (計画などの)立案
小袋,のう(動植物の内部にあり,特に液を含んだもの)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/04/09 08:21:07」(JST)

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The gestational sac is the large cavity of fluid surrounding the embryo. During early embryogenesis it consists of the extra-embryonic coelom, also called the chorionic cavity. By approximately 9 weeks of gestational age the amniotic sac has expanded to occupy the majority of its volume, eventually filling the entire space. The gestational sac is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy (IUP) exists, until the embryo is identified.

On obstetric ultrasound, the gestational sac is an anechoic (dark) space surrounded by a hyperchoic (white) rim.

A: Gestational sac (GS), B: Crown rump length (CRL) of embryo, C: Amniotic sac, D: Yolk sac

Structure

The extraembryonic coelom (or chorionic cavity) is shown between the two layers of extraembryonic mesoderm (labelled "mes.") in this image of an implanted embryo.

The extraembryonic coelom (or chorionic cavity) that constitutes the gestational sac for most part of the embryogenesis is a portion of the conceptus consisting of a cavity between Heuser's membrane and the Trophoblast.

During formation of the primitive yolk sac, some of the migrating hypoblast cells transdifferentiate into mesenchymal cells that fill the space between Heuser's membrane and the Trophoblast, forming the extraembryonic mesoderm. As development progresses, small lacunae begin to form within the extraembryonic mesoderm which become larger and form the extraembryonic coelom.

The extraembryonic coelom divides the extraembryonic mesoderm into two layers: extraembryonic splanchnopleuric mesoderm, which lies adjacent to Heuser's membrane around the outside of the primitive yolk sac, and extraembryonic somatopleuric mesoderm, which lies adjacent to the cytotrophoblast layer of the embryo.

The chorionic cavity is enclosed by the chorionic plate, which is composed of an inner layer of somatopleuric mesoderm and an outer layer of trophoblast cells.

It is spherical in shape, and usually located in the upper uterine fundus.

By approximately 9 weeks of gestational age, the amniotic sac has expanded to occupy the majority of the volume of the gestational sac, eventually expanding to reduce the extraembryonic coelom to a thin layer between the amnion membrane and the mesoderm. By then, the gestational sac is usually simply called the "amniotic sac".

Clinical significance

Ultrasound

Mean gestational sac diameter by gestational age. The blue line is the mean, and the green area delimits the 5th and the 95th percentiles.^[1]

The mean sac diameter (MSD) is an effective estimate of gestational age^[2] between 5 and 6 weeks, with an accuracy of about +/- 5 days.^[3]

The yolk sac and embryo should be readily identified when the gestational sac reaches a certain size—a yolk sac should be seen when gestational sac is 20mm and a fetal pole should be seen when the gestational sac reaches 25mm.

Gestational sacs can be identified via ultrasound and are generally identified by the following 4 characteristics:

Round or elliptical shape in longitudinal and transverse views
Surrounded by an echogenic rim (choriodecidual reaction)
Gestational sac is in uterine fundus
Sac is not directly midline, but implanted eccentrically (to one side of the uterine cavity line, without displacing it).

Ultrasound terms

Below are useful terms on ultrasound:^[4]

Echogenic - giving rise to reflections (echoes) of ultrasound waves
Hyperechoic – more echogenic (brighter) than normal
Hypoechoic – less echogenic (darker) than normal
Isoechoic – the same echogenicity as another tissue
Transvaginal ultrasonography - Ultrasound is performed through the vagina
Transabdominal ultrasonography - Ultrasound is performed across the abdominal wall or through the abdominal cavity

In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity. Fortunately, gestational sac, yolk sac and embryo are surrounded by hyperechoic (brighter) body tissues.

References

^ Papaioannou, George I.; Syngelaki, Argyro; Poon, Leona C.Y.; Ross, Jackie A.; Nicolaides, Kypros H. (2010). "Normal Ranges of Embryonic Length, Embryonic Heart Rate, Gestational Sac Diameter and Yolk Sac Diameter at 6–10 Weeks". Fetal Diagnosis and Therapy 28 (4): 207–219. doi:10.1159/000319589. ISSN 1421-9964.
Crown rump length before a gestational age of 6 weeks is extrapolated by assuming a gestational sac diameter of 0 at a gestational age of 2 weeks, corresponding to a fertilization age of 0 weeks. This extrapolated part is blurred because of uncertain values.
^ Karki DB, Sharmqa UK, Rauniyar RK (2006). "Study of accuracy of commonly used fetal parameters for estimation of gestational age". JNMA; journal of the Nepal Medical Association 45 (162): 233–7. PMID 17189967.
^ "Basic Imaging > Ultrasound of Early Pregnancy". Archived from the original on 2007-08-14. Retrieved 2007-10-13.
^ Zwingenberger, Allison (10 April 2007). "What do hyperechoic and hypoechoic mean?". DVM Journals.

UpToDate Contents

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1. 妊娠期間および出産予定日の出生前評価 prenatal assessment of gestational age and estimated date of delivery
2. 部位不明妊娠の超音波検査 ultrasonography of pregnancy of unknown location
3. 妊娠早期の臨床症状および診断 clinical manifestations and diagnosis of early pregnancy
4. 子宮外妊娠の臨床症状および診断 clinical manifestations and diagnosis of ectopic pregnancy
5. 頚管妊娠 cervical pregnancy

English Journal

Manual Compared With Electric Vacuum Aspiration for Abortion at Less Than 6 Weeks of Gestation: A Randomized Controlled Trial.

Dean G1, Colarossi L, Porsch L, Betancourt G, Jacobs A, Paul ME.
Obstetrics and gynecology.Obstet Gynecol.2015 May;125(5):1121-1129.
OBJECTIVE: To evaluate whether manual or electric vacuum aspiration results in greater immediate confirmation of completed abortion at less than 6 weeks of gestation.METHODS: Five hundred pregnant women presenting for surgical abortion with mean gestational sac diameter of less than 12 mm or no visi
PMID 25932839

Ultrasonographic parameters of cesarean scar defect in correlation with the outcome of early medical abortion.

Au HK1, Liu CF, Tzeng CR, Chien LW.
Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology.Ultrasound Obstet Gynecol.2015 Apr 11. doi: 10.1002/uog.14877. [Epub ahead of print]
OBJECTIVE: To determine whether cesarean scar defect (CSD) parameters assessed by transvaginal sonography (TVS) might impact the early medical abortion outcome.METHODS: Women with previous cesarean delivery who received oral mifepristone and misoprostol for medical abortion were reviewed retrospecti
PMID 25865778

Uncommon Implantation Sites of Ectopic Pregnancy: Thinking beyond the Complex Adnexal Mass.

Chukus A1, Tirada N, Restrepo R, Reddy NI.
Radiographics : a review publication of the Radiological Society of North America, Inc.Radiographics.2015 Apr 10:140202. [Epub ahead of print]
Ectopic pregnancy occurs when implantation of the blastocyst takes place in a site other than the endometrium of the uterine cavity. Uncommon implantation sites of ectopic pregnancy include the cervix, interstitial segment of the fallopian tube, scar from a prior cesarean delivery, uterine myometriu
PMID 25860721

Japanese Journal

症例報告子宮体部下方に胎囊を認め,前置・穿通胎盤をきたした既往帝王切開妊娠の一例

佐々木泉,萬来めぐみ,竹下直樹 [他]
千葉県産科婦人科医学会雑誌 = Chiba journal of obstetrics and gynecology 8(2), 135-138, 2015
NAID 40020334963

妊娠28週に卵管角の胎盤付着部位から子宮破裂を起こした1症例

大場智洋,長谷川潤一,新垣達也,仲村将光,松岡隆,市塚清健,関沢明彦
超音波医学 advpub(0), 2015
妊娠28週に卵管角部の子宮破裂を生じた1例を報告する．30歳，0回経妊，子宮手術の既往はない．妊娠26週2日，頻回な子宮収縮と性器出血を認め当科紹介になった．左側腹部に軟な腫瘤を触知した．経腹超音波検査で，腫瘤は，子宮卵管角から突出しており，中には胎盤が折りたたまれたように存在した．胎盤と子宮筋層にecho free spaceはなかった．左卵管角部の切迫子宮破裂を疑った．妊娠27週3日，超音波検 …
NAID 130004936717

妊娠28週に卵管角の胎盤付着部位から子宮破裂を起こした1症例

大場智洋,長谷川潤一,新垣達也,仲村将光,松岡隆,市塚清健,関沢明彦
超音波医学 42(2), 177-182, 2015
妊娠28週に卵管角部の子宮破裂を生じた1例を報告する．30歳，0回経妊，子宮手術の既往はない．妊娠26週2日，頻回な子宮収縮と性器出血を認め当科紹介になった．左側腹部に軟な腫瘤を触知した．経腹超音波検査で，腫瘤は，子宮卵管角から突出しており，中には胎盤が折りたたまれたように存在した．胎盤と子宮筋層にecho free spaceはなかった．左卵管角部の切迫子宮破裂を疑った．妊娠27週3日，超音波検 …
NAID 130004936713

Related Pictures

★リンクテーブル★

リンク元	「胎嚢」「GS」
関連記事	「gestation」「sac」

「胎嚢」

Gestational sac
	Contents in the cavity of the uterus seen at approximately 5 weeks of gestational age by obstetric ultrasonography.
	Artificially colored, showing gestational sac, yolk sac and embryo (measuring 3 mm as the distance between the + signs).
Details
Latin	saccus gestationalis, coeloma extraembryonicum, cavitas chorionica
Carnegie stage	6a
Days	12
Precursor	Heuser's membrane
Identifiers
Code	TE E5.8.0.0.1.0.1
Dorlands; /Elsevier	s_01/12716747
	Anatomical terminology

　　[★]

英: gestational sac, GS
ラ: capsula fetalis

妊娠4-5週で観察される。

「GS」

　　[★]

胎嚢 gestational sac

「gestation」

　　[★]

n.

計画を練ること、立案。妊娠、妊娠期間

関: conceive、gestational age、gestational period、gravid、pregnancy、pregnant

「sac」

　　[★]

n.

嚢

関: bursa、bursae、cysterna、pouch

[PapaioannouSyngelaki2010-1] Papaioannou, George I.; Syngelaki, Argyro; Poon, Leona C.Y.; Ross, Jackie A.; Nicolaides, Kypros H. (2010). "Normal Ranges of Embryonic Length, Embryonic Heart Rate, Gestational Sac Diameter and Yolk Sac Diameter at 6–10 Weeks". Fetal Diagnosis and Therapy 28 (4): 207–219. doi:10.1159/000319589. ISSN 1421-9964.
Crown rump length before a gestational age of 6 weeks is extrapolated by assuming a gestational sac diameter of 0 at a gestational age of 2 weeks, corresponding to a fertilization age of 0 weeks. This extrapolated part is blurred because of uncertain values.

[pmid17189967-2] Karki DB, Sharmqa UK, Rauniyar RK (2006). "Study of accuracy of commonly used fetal parameters for estimation of gestational age". JNMA; journal of the Nepal Medical Association 45 (162): 233–7. PMID 17189967.

[3] "Basic Imaging > Ultrasound of Early Pregnancy". Archived from the original on 2007-08-14. Retrieved 2007-10-13.

[Ultrasound_Terms-4] Zwingenberger, Allison (10 April 2007). "What do hyperechoic and hypoechoic mean?". DVM Journals.

匿名

検索

案内

案内

gestational sac