Final answer:
Fetal ultrasound is the most accurate method for determining gestational age and is also safe for use during pregnancy, unlike other imaging studies which may involve radiation.
Step-by-step explanation:
The most accurate measurement available to determine gestational age is c) Fetal ultrasound. This method allows healthcare providers to visualize the fetus's development and measure key anatomical features to estimate the gestational age accurately. Fetal ultrasounds are considered safe for use during pregnancy and can provide valuable information for dating the pregnancy, especially when compared with other methods such as fundal height measurement, Last Menstrual Period (LMP), or kick counts, which can be less precise or more variable.
When discussing the safety of imaging studies during pregnancy, c) ultrasounds are known to be the safest option, as opposed to CT scans, PET scans, and X-rays, which involve radiation exposure that may pose risks to the developing fetus. Therefore, for the purposes of determining gestational age and assessing fetal development, fetal ultrasound is the preferred and most accurate method.