There are many terms used within the health field for monitoring growth, many of which have very specific definitions that sometimes differ from common or lay-usage.
BMI stands for Body Mass Index, which is calculated by dividing the weight (in kilograms) by the height (im metres) squared. BMI = Weight/Height<sup>2</sup>
This is the standard method to account for height in assessing if a person is over or underweight, and is generally very useful. In the adult world, it is distorted in individuals with very high muscle mass, as muscle is generally much heavier than other tissue (including fat). In children, the ideal BMI changes with age, and as such it should be viewed on a BMI-for-Age growth chart.
To see standard BMI interpretations for adults, go to the Wikipedia BMI page.
A dietitian is a health professional who has specific training in nutrition and uses this training to promote good health. In Canada, the term is protected and governed by a provincial regulatory body, and dietitians are regulated by and accountable to this body. To be certified, dietitians complete a bachelor's degree specializing in food and nutrition and have completed supervised practical training through an approved university, hospital or community setting. (This is in contrast to nutritionist which is not regulated in Canada, and as such does not denote any particular credentials or expertise)
- due date
- the approximate expected date of delivery. This date is the same as the estimated date of confinement (EDC) and the estimated due date (EDD). There is considerable variation between normal pregnancies, and as such any baby delivered between 37 and 42 weeks gestation are considered to be full term. The due date is typically calculated by one of two ways:
Counting weeks of gestation (40 weeks gestational age):
- Starting from the first day of the last menstrual period, count forward 40 weeks. While this was initially awkward to do with calendars, the development of pregnancy wheels and the advance of technology has allowed this calculation to be done with ease. Counting weeks of gestation is the standard timeline used to track a pregnancy.
- Named after a German obstetrician who developed it, Franz Naegele (1778-1851), this method involves starting with the first day of the last menstrual period, adding a year, subtracting three months, and adding a week. The result is approximately 40 weeks, although there is some variation due to the changing lengths of the various months. For example:
Last menstrual period started: September 24, 2012
Add one year: September 24, 2013
Subtract three months: June 24, 2013
Add one week: July 1, 2013
Due Date: July 1, 2013
In this example, both methods produce the same birth date.
- embryonic age
The age, in weeks, of a pregnancy from the date of conception. In a typical female with a 28 day cycle, ovulation tends to occur approximately two weeks since the beginning of the last menstrual period. Fertilization/conception may occur within a few days of this, although there are many factors that can change the precise timing of this.
While this term does refer to the actual age of the 'baby' since it was conceived, it is difficult to accurately calculate. This is a term used largely in research communities, and is generally avoided within general public contexts due to the difficulty in calculating it and the tendency for confusion with gestational age.
Throughout this site, the term gestational age is used instead.
- estimated date of confinement
see due date
- estimated due date
see due date
- failure to thrive
Failure to thrive is a descriptive term that refers to failure to grow appropriately. This usually refers to the child's weight not keeping up with the typical growth for his or her age, resulting in their growth beginning to cross percentile lines (growth curves). This term could occasionally also refer to linear growth (height) or head circumference not keeping up with the child's established percentile growth curve. Weight is usually the first parameter to drop off, followed by height and then finally head circumference.
- full term
This refers to any baby that was delivered between 37 and 42 weeks of gestation.
- gestational age
This is the age of the child beginning from the beginning of the last menstrual period (LMP) of the mother, prior to the beginning of the pregnancy. It is measured in weeks, with 40 weeks being the due date. A full-term baby is considered one born between 37 and 42 weeks of age.
(The actual conception often occurs 2 weeks after the beginning of the last menstrual period, but this date is not widely used. If it is being used, age from conception is referred to as fetal or embryonic age.)
- growth curve
Another term for a percentile or percentile curve. This is the curve on a graph that represents a child's typical growth over time. Once the child has been seen to be following a particular growth curve, they can be assumed to continue to follow it.
Any big or persistent changes from this curve may be reason to review his or her growth with a pediatrician, family physician or dietitian.
For more information, please see "percentile".
- growth standard
This refers to optimal, rather than typical, growth. A growth standard refers to how a child should grow under optimal conditions, and may be applied across ethnicity and cultures.
- last menstrual period
Within pregnancy and fertility contexts, this term refers specifically to the first day of the last menstrual period. It is also known by the abbreviation, LMP.
A obstetrician is a medical doctor who has gone on to do a residency (specialization) in in-utero fetal development, or development of the baby from conception to delivery. In contrast to other health professionals who deliver babies (family physicians and midwives), an obstetrician is also a surgeon, and thus able to perform a cesarean section (delivering the baby through the abdomen through a surgical incision) should it be required. In a typical pregnancy, they are usually involved by request of the primary care provider at some point during the pregnancy, and they would follow them up until and just after childbirth. After birth, their chief duty is to the mother, while another physician or nurse would be looking after the newborn baby. They usually also train in gynecology, which refers to aspects of women's health involving their ovaries, fallopian tubes, uterus, vagina, urethra, general pelvis and often bladder.
A pediatrician is a medical doctor who has gone on to do a residency (specialization) in child-related medicine and health. They may further specialize from here (either by age groups, such as into neonatology, or by medical area, such as respirology or cardiology).
Technically, a percentile is a value below which that percent of the population exist. For example, at the 25th percentile of height, 25% of the population will be the same height or shorter. Similarly, at the 99th percentile, 99% of people the same age will be the same height or shorter, and only 1% will be taller. The large population studies done to establish growth charts found that individuals at the same point tended to follow similar growth parameters. You can therefore find 'percentile growth curves' on these charts. To avoid cluttering the charts, only selected percentiles are displayed, though these are usually good enough to visualize typical growth trends.
Children, once their growth is seen to have picked a particular percentile curve, tend to follow that curve throughout much of their development. Any significant change, especially one that crosses multiple percentile curves or persists on multiple measurements, should be investigated to determine the significance or potential causes.
This term refers to any baby delivered after the beginning of the 42nd week of gestation. It is significant as after this point the placenta (the main source of nutrition and oxygen for the baby prior to delivery) begins to have a decline in function. Given this, attempts to induce delivery with medication may begin as this point is neared. The specific dates that induction is attempted and cesarean sections (surgery) are performed vary between jurisdictions and hospitals.
This refers to any baby delivered prior to the completion of the 37th week of gestation. The earlier in development the baby is delivered, the more significant the health challenges that may be presented (often with regards to lung function, ability to feed and digest food, as well as the ability to store and retrieve energy in fat or glycogen energy stores).