A. “Gestational age” (or “menstrual age”) is the time elapsed between the first day of the last normal menstrual period and the day of delivery. The first day of the last menstrual period occurs approximately 2 weeks before ovulation and approximately 3 weeks before implantation of the blastocyst. Minor inaccuracy 4–6 days if cycle is regular and recall is accurate. Gestational age is conventionally expressed as completed weeks.
B. “Chronological age” (or “postnatal” age) is the time elapsed after birth. It is usually described in days, weeks, months, and/or years.
C. Postmenstrual age is the time elapsed between the first day of the last menstrual period and birth (gestational age) plus the time elapsed after birth (chronological age). Usually described in number of weeks and is most frequently applied during the perinatal period beginning after the day of birth. For postnatal management reason, a week + days can be used.
D. “Corrected age” (or “adjusted age”) is a term most appropriately used to describe children up to 3 years of age who were born preterm. Represents the age of the child from the expected date of delivery.
Corrected age = chronological age- [ ( 40wks – Gestational Age)X mth/4 weeks]
E. “Conceptional age” is the time elapsed between the day of conception and the day of delivery. Because assisted reproductive technologies accurately define the date of fertilization or implantation, a precise conceptional age can be determined in pregnancies resulting from such technologies.
To avoid confusion, the term “gestational age” should be used. The terms “conceptional age” and “postconceptional age,” reflecting the time elapsed after conception, should not be used.
Gestational age is often determined by the “best obstetric estimate,” which is based on a combination of the first day of last menstrual period, physical examination of the mother, prenatal ultrasonography, and history of assisted reproduction.
The best obstetric estimate is necessary because of gaps in obstetric information and the inherent variability (as great as 2 weeks) in methods of gestational age estimation.
Postnatal physical examination of the infant is sometimes used as a method to determine gestational age if the best obstetric estimate seems inaccurate.
Therefore, methods of determining gestational age should be clearly stated so that the variability inherent in these estimations can be considered when outcomes are interpreted
SOURCE: Pediatrics November 2004, VOLUME 114 / ISSUE 5 Age Terminology during the Perinatal Period
Terminologies related to weeks of Gestation
In a joint Committee Opinion, The American College of Obstetricians and Gynecologists (The College) and the Society for Maternal-Fetal Medicine (SMFM) are discouraging use of the general label ‘term pregnancy’ and replacing it with a series of more specific labels: ‘early term,’ ‘full term,’ ‘late term,’ and ‘post term.’ The following represent the four new definitions of ‘term’ deliveries:
- Early Term: Between 37 weeks 0 days and 38 weeks 6 days
- Full Term: Between 39 weeks 0 days and 40 weeks 6 days
- Late Term: Between 41 weeks 0 days and 41 weeks 6 days
- Post term: Between 42 weeks 0 days and beyond
Preterm: All babies born at less than 37 weeks gestation
- Late Preterm: 34 weeks to 36 weeks +6 days
- Preterm: 23 weeks to 33weeks + 6 days