Premature baby - Mijukuji

Japanese: 未熟児 - みじゅくじ

Premature and low birth weight babies
Generally, a baby weighing less than 2,500g at birth is called a premature baby. This includes low birth weight babies born prematurely (before 37 weeks of gestation) and full-term low birth weight babies (after 37 weeks of gestation) who weigh less than 2,500g.
The Japanese Pediatric Society defines a baby weighing less than 2,500g as a low birth weight baby, regardless of the number of weeks since birth, and the term "premature baby" is, in principle, a term that indicates maturity regardless of weight. However, because the term "premature baby" was used as a synonym for "low birth weight baby" for a long time, it is still often used today as a general term for babies weighing less than 2,500g at birth.
What low birth weight babies are called: A baby weighing less than 2500g is called a low birth weight baby, a baby weighing less than 1500g is called a very low birth weight baby, and a baby weighing less than 1000g is called an extremely low birth weight baby.
Causes of premature birth include smoking, giving birth at a young or advanced age, heart disease, kidney disease, pregnancy-induced hypertension (pregnancy toxemia), and placental insufficiency, but the most common cause is premature birth (premature birth).
How premature babies are named based on the gestational age : babies born between 22 and 37 weeks are called premature babies, babies born between 22 and 28 weeks are called extremely premature babies, and babies born between 28 and 37 weeks are called premature babies of 28 weeks or more gestation. The earlier the baby is, the more difficult it will be for them to live outside the womb.
Lower mortality ratesThe mortality rate of premature babies has been decreasing due to the widespread use of respiratory management medical equipment and monitoring devices, an increase in facilities such as NICUs (neonatal intensive care units), and cooperation between local facilities such as maternal transport and doctor's cars. However, the mortality rate of very low birth weight and extremely low birth weight babies remains high.

Source: Shogakukan Home Medical Library Information

Japanese:

未熟児と低出生体重児（ていしゅっしょうたいじゅうじ）
　ふつう、出生時の体重が2500g未満の赤ちゃんを未熟児と呼んでいます。このなかには、早期産（そうきさん）低出生体重児（在胎（ざいたい）37週未満）で出生した体重の少ない赤ちゃんと、正期産（せいきさん）低出生体重児（在胎37週以降）でも、2500g未満の体重しかない赤ちゃんも含まれています。
　日本小児科学学会では、生まれた週数に関係なく、2500g未満の赤ちゃんを低出生体重児とし、未熟児とは、原則として体重にかかわりなく成熟度を示す用語としています。しかし、未熟児ということばは長い間、低出生体重児の同義語として用いられていたために、現在も、出生体重2500g未満の赤ちゃんの総称名として用いられている場合が多いのです。
　低出生体重児の呼び方
　2500g未満を低出生体重児、1500g未満を極低出生体重児、1000g未満を超低出生体重児と呼びます。
　未熟児の生まれる原因としては、喫煙、若年・高年（齢）出産、心臓病、腎臓（じんぞう）病、妊娠高血圧症候群（妊娠中毒症）、胎盤機能不全（たいばんきのうふぜん）などがありますが、いちばん多いのが早産（そうざん）（「早産」）です。
　妊娠期間による早産児の呼び方
　在胎（ざいたい）22週以上37週未満を早産児、在胎22週以上28週未満を超早産児、在胎28週以上37週未満を在胎28週以上の早産児と呼び、週数が浅いほど胎外生活がむずかしくなります。
　低くなった死亡率
　未熟児の死亡率は、呼吸管理の医療機器や監視装置の普及、ＮＩＣＵ（新生児集中治療室）などの施設の増加、母体搬送・ドクターカーなどの地域施設の連携により減少してきていますが、極低出生体重児や超低出生体重児の死亡率は、いまだに高いのが現状です。

出典　小学館家庭医学館について　情報

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