What does the fern test check for during pregnancy?

The fern test checks for the presence of amniotic fluid during pregnancy. This test is based on the observation that when amniotic fluid is present, it contains a high level of sodium chloride, which promotes the crystallization of the fluid into a fern-like pattern when spread on a glass slide and dried. The presence of this characteristic pattern indicates that the fluid is indeed amniotic, confirming a rupture of membranes.

When examining the other options, fetal growth is primarily assessed through ultrasound measurements and monitoring fetal heart tones, while cervical dilation is evaluated during a pelvic examination in labor. Maternal hydration, although important to monitor in pregnancy, does not specifically pertain to the fern test and would be evaluated through other clinical assessments. Thus, the correct answer regarding what the fern test assesses is the presence of amniotic fluid.