Translation guide
In Japanese, the term for a premature baby depends on context and formality. The most common medical term is 未熟児, while everyday conversation may use descriptive phrases. This guide covers medical, conversational, and related expressions.
未熟児
premature baby (medical)
早く生まれた赤ちゃん
premature baby (casual)
Referring to a premature baby in medical or formal contexts.
Standard medical term for a premature infant. Used in hospitals, official documents, and formal discussions.
未熟児医療は大きく進歩した。
Medical care for premature babies has advanced greatly.
Literally 'early-birth baby'. Also used in medical contexts, emphasizing the early birth rather than the immaturity.
早産児のケアには特別な注意が必要だ。
Care for preterm infants requires special attention.
Talking about a premature baby in casual conversation.
Descriptive phrase meaning 'baby born early'. Natural and easy to understand in everyday speech.
友達の赤ちゃんは早く生まれた赤ちゃんだったけど、今は元気だよ。
My friend's baby was born early, but he's healthy now.
Means 'baby born small'. Often used when the baby's low birth weight is the focus, which is common with prematurity.
小さく生まれた赤ちゃんは、最初は大変だった。
The baby born small was difficult at first.
Specifically referring to a baby with low birth weight, often associated with prematurity.
Medical term for low birth weight infant (under 2500g). Frequently used in neonatal care contexts.
低出生体重児の増加が問題になっている。
The increase in low birth weight infants is a problem.
Often used interchangeably with low birth weight, though technically distinct. In common usage, 未熟児 implies both prematurity and low weight.
未熟児 (mijukuji) focuses on the baby's immaturity (underdeveloped organs, low weight), while 早産児 (sōzanji) emphasizes the early timing of birth. In practice, they are often used interchangeably, but 未熟児 is more common in general medical contexts.
未熟児網膜症は、未熟児に起こりやすい目の病気です。
Retinopathy of prematurity is an eye disease common in premature babies.
In casual conversation, Japanese speakers often avoid technical terms and use phrases like 早く生まれた (born early) or 小さく生まれた (born small). This is more natural when sharing personal stories.
Because I was born premature, my weight was low.