Gestational age: MedlinePlus Medical Encyclopedia (2024)

FAQs

Gestational age: MedlinePlus Medical Encyclopedia? ›

It is measured in weeks, from the first day of the woman's last menstrual cycle to the current date. A normal pregnancy can range from 38 to 42 weeks. Infants born before 37 weeks are considered premature. Infants born after 42 weeks are considered postmature.

First Trimester Dating: Sonographic assessment within the first 13 weeks and 6 days will provide the most accurate estimate of gestational age. Both transvagin*l and transabdominal approaches may be used. However, the transvagin*l approach may provide a more clear and accurate view of early embryonic structures.

Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11 15 16 17 18.

Sometimes the dates can be more than a week off and sometimes even as much as 4 weeks. An early obstetric ultrasound performed at approximately 8 weeks where a crown rump length (the CRL) is measured precisely predicts an estimated due date accurately.

As menstrual dates can be inaccurate (or not recalled), the best method for gestational age estimation is ultrasound measurement of the fetal crown-rump length in the first trimester.

In the second and third trimesters, fetal head, body, and extremity measurements have been commonly used to assess gestational age. Those parameters most commonly measured include biparietal diameter,^{20,21,22,23,24,25,26,27,28} head circumference,^29,30 abdominal circumference,^{31,32,33,34,35} and femur length.

To calculate your gestational age, or many weeks pregnant you are, you need to know the date of your Last Menstrual Period (LMP). Starting from this date, count the weeks up to today's date. This number will correspond to the number of weeks pregnant.

It is possible for gestational age to be inaccurate by up to 2 weeks, even with an accurate LMP date confirmed by other tests. All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

Week 4 of pregnancy

For example, a fertilised egg may have implanted in your womb just 2 weeks ago, but if the first day of your last period was 4 weeks ago, this means you're officially four weeks pregnant! Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.

Keep in mind that you will be two weeks further along in your pregnancy than you might think; for example, if you had sex and conceived two weeks ago, and you have a 28 day cycle, then you are actually four weeks pregnant.

Do you go by gestational age or fetal age? ›

Gestational age (GA) refers to the length of pregnancy after the first day of the last menstrual period (LMP) and is usually expressed in weeks and days. This is also known as menstrual age. Conceptional age (CA) is the true fetal age and refers to the length of pregnancy from the time of conception.

By 2020, less than a third (30%) of births occurred at ≥40 weeks, with 39 weeks being the most common gestational age. The mean gestational age in 1990 was 39.1 weeks (S.D.

Fetal viability is generally considered to begin at 23 or 24 weeks gestational age in the United States. There is no sharp limit of development, gestational age, or weight at which a human fetus automatically becomes viable.

The American College of Obstetricians and Gynecologists (ACOG) recommends ultrasound measurement during the first trimester (up to and including 13 6/7 weeks of gestation) as the most accurate method to establish or confirm gestational age.

The principal method used to postnatally estimate gestational age (GA) is the new Ballard score, which combines physical and neurologic criteria (table 1 and figure 1). The new Ballard score is easier to administer than the longer Dubowitz method.

A dating scan is usually done between 8 and 14 weeks of pregnancy (most often before 12 weeks). At this time, most babies of the same gestational age are about the same size. If your doctor or midwife also recommends a nuchal translucency scan, they may try to arrange it between 11 and 13 weeks.

FL (femur length): The length of the femur bone. CRL (crown-rump length): The length from the top of the head to the bottom. This measurement is more accurate in the first trimester. After 12 weeks of pregnancy, the parameters above are better at giving an overall assessment of growth.