A comparison of biparietal diameter measurements using a real-time scanner and a conventional scanner equipped with a coded cephalometry system.

In 131 patients a comparison was made between measurements obtained using a real-time scanner and those obtained using a conventional "B" scanner with an attached "coded cephalometry system": 69 per cent of the readings agreed within +/- 2 mm and, when the "B" scan reading was considered "good", 90 percent fell within this range. Between 14 and 28 weeks, gestational age diagnoses using the two methods were within one week of each other in 88 of 89 patients.