North American Registry of Midwives (NARM) Practice Exam

During the first half of pregnancy, how accurately can ultrasound predict gestational age?

1. Within five days

2. Within ten days

3. Within fifteen days

4. Within twenty days

The correct answer is: Within ten days

Ultrasound is a key tool in obstetrics for estimating gestational age, especially during the first trimester when the fetal structures are well-defined. The ability to accurately predict gestational age using ultrasound peaks in this early phase, primarily due to the consistent growth patterns of embryos and fetuses at this stage. When determining gestational age within the first trimester, measurements such as crown-rump length are taken, which provide a precise indication of the embryo's size relative to developmental milestones. Studies have shown that ultrasounds conducted during this period can typically predict gestational age within a range of ten days. Beyond this timeframe, factors such as individual variations in fetal growth patterns can lead to less accuracy. The other options suggest varying levels of uncertainty that do not reflect the high level of precision available in the first trimester. For gestational age estimation, a ten-day margin is considered the standard, making this the most accurate statement regarding ultrasound capabilities during the early stages of pregnancy.