**Core Concept**
Preeclampsia is a pregnancy complication characterized by new-onset hypertension and proteinuria after 20 weeks of gestation. Sonographic findings can aid in the early detection and diagnosis of preeclampsia by identifying changes in maternal and fetal well-being.

**Why the Correct Answer is Right**
The correct sonographic finding that suggests the development of preeclampsia is **abnormal umbilical artery Doppler waveforms**. This is due to the presence of increased vascular resistance in the placenta, which can lead to fetal growth restriction and other complications. Abnormal umbilical artery Doppler waveforms are often characterized by a notch or a reversal of the diastolic flow, indicating impaired placental perfusion.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased uterine artery resistance may be associated with preeclampsia, but it is not the most specific sonographic finding. Increased uterine artery resistance is a marker of placental insufficiency, but it can also be seen in other conditions.

**Option B:** Fetal growth restriction (FGR) is a common complication of preeclampsia, but it is not a specific sonographic finding that suggests the development of preeclampsia. FGR can be caused by various factors, including placental insufficiency, maternal hypertension, and other conditions.

**Option C:** Placental thickness is not a specific sonographic finding that suggests the development of preeclampsia. While placental thickness can be affected by preeclampsia, it is not a reliable marker for the condition.

**Option D:** Maternal cardiac output is not a sonographic finding that can be directly measured during pregnancy. While maternal cardiac output may be affected by preeclampsia, it is not a specific sonographic finding that suggests the development of the condition.

**Clinical Pearl / High-Yield Fact**
Abnormal umbilical artery Doppler waveforms are a critical sonographic finding that suggests the development of preeclampsia. It is essential to monitor fetal well-being closely in patients with abnormal umbilical artery Doppler waveforms and to intervene promptly to prevent fetal growth restriction and other complications.

**Correct Answer: A. Abnormal umbilical artery Doppler waveforms**