■	最終月経	さいしゅうげっけい	last menstrual period (LMP)
■	受胎	じゅたい	conception
■	在胎週数	ざいたいしゅうすう	gestational age (GA)
■	受胎後週数	じゅたいごしゅうすう	post-conceptional age (PCA)
■	妊娠週数	にんしんしゅうすう	post-menstrual age (PMA)
■	暦年齢, 生後週数	れきねんれい, せいごしゅうすう	chronological age (CH)
■	修正在胎期間	しゅうせいざいたいきかん	corrected gestational age (CGA)
■	修正月齢	しゅうせいげつれい	corrected age (CA)

□ The above terms are used to describe the age of babies who were born prematurely.

last menstrual period (LMP) (最終月経)

The first day of the last menstrual period before conception.

conception (受胎)

The mid-point in the menstrual cycle after the last menstrual period, i.e., two weeks after the LMP.

gestational age (GA) (在胎週数)

(1) Age of the fetus as measured from the LMP. Often referred to as "weeks of gestation."
gestational age

(2) Syn: corrected gestational age (1). Probably a rarely used abbreviated form.
Calculating Corrected Age

post-menstrual age (PMA) (妊娠週数)

(1) Gestational age (1) plus the weeks since birth. Syn: corrected gestational age (2).
Human Sentience Before Birth.

(2) Gestational age (1).
Gestational Age Terminology

Note: Possibly coined after "post-conceptional age" to distinguish from it. 妊娠週数 cannot be used for sense (1), instead see corrected gestational age (2).

post-conceptional age (PCA) (受胎後週数)

Age of the fetus or baby as measured from conception. Compare with post-menstrual age (1).

chronological age (CH) (暦年齢, 生後週数)

Age of the baby as measured from birth. Often just "age" as in "at four weeks of age."

corrected gestational age (CGA) (修正在胎期間）

(1) Age of the baby minus the weeks born premature. Syn: corrected age.
General Medical Information IV

(2) The gestational age (1) plus the weeks after birth. Syn: post-menstrual age (1).
Music therapy for premature babies in intensive care

corrected age (CA) (修正月齢)

The chronological age minus the number of weeks born premature.

• Age is most commonly measured in weeks, except possibly for corrected age, which is sometimes counted in months for babies up to two years old.
• The synonyms apply only to the English terms. The many-to-one and one-to-many relationships of the Japanese and English are not shown.
• Definitions are ordered according to most common usage.
• Explanation about the use of post-menstrual and post-conceptional age to date a pregnancy
  http://www.care.org.uk/resource/pub/fs/fs_cont.htm
  http://www.care.org.uk/resource/pub/fs/fs11.htm
• Explanation about use of post-menstrual age to date the age of a premature infant (at least to 44 weeks).
  http://www.nichd.nih.gov/cochrane/Woodgate/table03.html
  http://www.nichd.nih.gov/cochrane/DHS5/DHS.HTM
• In the following chart, an attempt was made to clarify usage by showing where each sense of a term applies. There is considerable confusion between some of these terms (see Background Information). Often the context will determine the intended meaning. The chart uses a premature birth at 28 weeks gestational age as an example.

Background Information

• The common concept of human age—how many months or years since birth—is not useful in treating or studying premature infants or studying fetal development, so different conventions for measuring age were developed. These conventions differ according to the requirements of the discipline. For example, neonatologists, obstetricians, and scientists researching fetal development have different viewpoints and requirements. However, each discipline uses the same or similar words, sometimes with different meanings. To add to the problem, there are sometimes conflicting or confused definitions and usages of these terms even within a single discipline. Gestational age, corrected gestational age, and corrected age, for instance, are used synomously by some (Calculating Corrected Age). Misuse of PCA is noted by at least one Web page (Gestational Age Terminology), and some of the terms are not known by specialists in the field, as discovered in a direct survey of two neonatologists. In an article in a Japanese medical journal, "PCA" was used as an abbreviation for 修正在胎期間.
• The age of the baby is vital to determining its health, since size compared to age is one index of development and health.
• Beside cases of in vitro fertilization, no one knows exactly when a mother becomes pregnant, thus the date of conception is estimated as the mid-point in the menstrual cycle, 2 weeks from the first day of the last menstrual period.
• A term birth, or normal birth, is anywhere from 37 to 42 weeks of gestation. The average is 40 weeks.
• Premature babies are kept in the hospital until their bodyweight reaches about 2500 g and they can be fed with a bottle. Their discharge from the hospital often coincides with 37 to 40 weeks gestational age (i.e., they leave the hospital when they would have if the pregnancy had gone to term, though some stay longer).

This entry was created by Paul Flint.

Created 2003-01-13. Minor revisions by PF 2003-01-23.