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What is AOG in medical?

Published in Gestational Age Assessment 2 mins read

AOG in a medical context commonly refers to Assessment of Gestational Age. This assessment determines how far along a pregnancy is, typically in weeks and days. It plays a vital role in prenatal care and delivery management.

Assessment of Gestational Age by Ultrasound

Ultrasound is a common method used for AOG determination. It involves measuring certain fetal characteristics to estimate gestational age.

  • First Trimester: Ultrasound in the first trimester is the most accurate method for dating a pregnancy. Crown-rump length (CRL), the measurement from the top of the baby's head to the bottom of the buttocks, is used for dating.
  • Second Trimester: Measurements such as biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) are used. Accuracy decreases as the pregnancy progresses.
  • Third Trimester: Ultrasound dating becomes less precise in the third trimester.

Why is AOG Important?

Accurate assessment of gestational age is crucial for:

  • Prenatal Care: Helps schedule appropriate screenings and tests.
  • Delivery Management: Important for deciding when to induce labor, especially in cases of post-term pregnancy.
  • Assessing Fetal Growth: Helps to identify potential growth restrictions or macrosomia (excessively large baby).
  • Neonatal Care: Crucial for anticipating potential problems and planning neonatal care.

Methods for AOG Assessment:

Besides ultrasound, other methods can be used. These include:

  1. Last Menstrual Period (LMP): Naegele's rule is a common calculation method based on the first day of the last menstrual period. However, this method assumes a regular 28-day cycle and is less accurate if the cycle is irregular.
  2. Physical Examination: In early pregnancy, a pelvic exam can provide an estimate of gestational size.

Factors Affecting AOG Accuracy

  • Timing of Ultrasound: Earlier ultrasounds are generally more accurate.
  • Fetal Position: A suboptimal fetal position can make measurements difficult.
  • Multiple Gestation: Dating a multiple pregnancy can be more challenging.