A primigravida unsure of her last menstrual period is estimated to be at 22 weeks' gestation. What data supports this conclusion?

The fundal height measurement is a reliable indicator of gestational age, especially when the uterus grows and ascends in the abdomen. At approximately 20 weeks of gestation, the fundus is typically at the level of the umbilicus. Therefore, if the fundus is at the umbilicus, this supports the estimation that the pregnancy is around 22 weeks along, as it indicates that fetal development is consistent with that timeframe.

While the presence of fetal heart tones is a positive sign of pregnancy and fetal well-being, it does not provide a specific measurement correlating to gestational age. Similarly, abdominal measurements can provide some information, but they are less standardized and can vary significantly among individuals. A positive pregnancy test is also a sign of pregnancy but does not indicate the gestational age. Thus, the fundal height at the umbilicus is the most direct piece of evidence for estimating gestational age in this scenario.