Which maternal condition is considered a contraindication for the application of internal monitoring devices?

A. Unruptured membranes: Internal fetal monitoring devices, such as a fetal scalp electrode or intrauterine pressure catheter, require rupture of membranes to access the amniotic fluid and fetal scalp. Attempting insertion with intact membranes increases the risk of trauma, infection, and procedural failure. B. Cervix is dilated to 4 cm: A cervical dilation of 4 cm is typically sufficient for safe internal monitoring once membranes are ruptured. The degree of dilation itself does not prevent application, provided other criteria for internal monitoring are met. C. External monitors are currently being used: External monitoring is noninvasive and can be used concurrently or as an initial step. The presence of external monitors does not contraindicate internal monitoring; internal devices are considered when more accurate fetal heart rate or contraction data are needed. D. Fetus has a known heart defect: Some fetal heart defects may alter baseline heart rate or variability but do not automatically preclude the use of internal monitoring devices. Internal monitoring can still be applied safely if membranes are ruptured and other clinical criteria are met.